Artykuły w czasopismach na temat „Chromosomes”
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1
Zhao, J. T., M. Frommer, J. A. Sved i A. Zacharopoulou. "Mitotic and polytene chromosome analyses in the Queensland fruit fly, Bactrocera tryoni (Diptera: Tephritidae)". Genome 41, nr 4 (1.08.1998): 510–26. http://dx.doi.org/10.1139/g98-053.
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The Queensland fruit fly, Bactrocera tryoni, like the Mediterranean fruit fly, Ceratitis capitata, has a diploid complement of 12 chromosomes, including five pairs of autosomes and a XX/XY sex chromosome pair. Characteristic features of each chromosome are described. Chromosomal homology between B. tryoni and C. capitata has been determined by comparing chromosome banding pattern and in situ hybridisation of cloned genes to polytene chromosomes. Although the evidence indicates that a number of chromosomal inversions have occurred since the separation of the two species, synteny of the chromosomes appears to have been maintained.Key words: tephritid fruit fly, Bactrocera tryoni, polytene chromosomes, in situ hybridisation, chromosomal homology.
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Spell, R. M., i C. Holm. "Nature and distribution of chromosomal intertwinings in Saccharomyces cerevisiae". Molecular and Cellular Biology 14, nr 2 (luty 1994): 1465–76. http://dx.doi.org/10.1128/mcb.14.2.1465-1476.1994.
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To elucidate yeast chromosome structure and behavior, we examined the breakage of entangled chromosomes in DNA topoisomerase II mutants by hybridization to chromosomal DNA resolved by pulsed-field gel electrophoresis. Our study reveals that large and small chromosomes differ in the nature and distribution of their intertwinings. Probes to large chromosomes (450 kb or larger) detect chromosome breakage, but probes to small chromosomes (380 kb or smaller) reveal no breakage products. Examination of chromosomes with one small arm and one large arm suggests that the two arms behave independently. The acrocentric chromosome XIV breaks only on the long arm, and its preferred region of breakage is approximately 200 kb from the centromere. When the centromere of chromosome XIV is relocated, the preferred region of breakage shifts accordingly. These results suggest that large chromosomes break because they have long arms and small chromosomes do not break because they have small arms. Indeed, a small metacentric chromosome can be made to break if it is rearranged to form a telocentric chromosome with one long arm or a ring with an "infinitely" long arm. These results suggest a model of chromosomal intertwining in which the length of the chromosome arm prevents intertwinings from passively resolving off the end of the arm during chromosome segregation.
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Spell, R. M., i C. Holm. "Nature and distribution of chromosomal intertwinings in Saccharomyces cerevisiae." Molecular and Cellular Biology 14, nr 2 (luty 1994): 1465–76. http://dx.doi.org/10.1128/mcb.14.2.1465.
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To elucidate yeast chromosome structure and behavior, we examined the breakage of entangled chromosomes in DNA topoisomerase II mutants by hybridization to chromosomal DNA resolved by pulsed-field gel electrophoresis. Our study reveals that large and small chromosomes differ in the nature and distribution of their intertwinings. Probes to large chromosomes (450 kb or larger) detect chromosome breakage, but probes to small chromosomes (380 kb or smaller) reveal no breakage products. Examination of chromosomes with one small arm and one large arm suggests that the two arms behave independently. The acrocentric chromosome XIV breaks only on the long arm, and its preferred region of breakage is approximately 200 kb from the centromere. When the centromere of chromosome XIV is relocated, the preferred region of breakage shifts accordingly. These results suggest that large chromosomes break because they have long arms and small chromosomes do not break because they have small arms. Indeed, a small metacentric chromosome can be made to break if it is rearranged to form a telocentric chromosome with one long arm or a ring with an "infinitely" long arm. These results suggest a model of chromosomal intertwining in which the length of the chromosome arm prevents intertwinings from passively resolving off the end of the arm during chromosome segregation.
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Singchat, Worapong, Thitipong Panthum, Syed Farhan Ahmad, Sudarath Baicharoen, Narongrit Muangmai, Prateep Duengkae, Darren K. Griffin i Kornsorn Srikulnath. "Remnant of Unrelated Amniote Sex Chromosomal Linkage Sharing on the Same Chromosome in House Gecko Lizards, Providing a Better Understanding of the Ancestral Super-Sex Chromosome". Cells 10, nr 11 (1.11.2021): 2969. http://dx.doi.org/10.3390/cells10112969.
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Comparative chromosome maps investigating sex chromosomal linkage groups in amniotes and microsatellite repeat motifs of a male house gecko lizard (Hemidactylus frenatus, HFR) and a flat-tailed house gecko lizard (H. platyurus, HPL) of unknown sex were examined using 75 bacterial artificial chromosomes (BACs) from chicken and zebra finch genomes. No massive accumulations of microsatellite repeat motifs were found in either of the gecko lizards, but 10 out of 13 BACs mapped on HPL chromosomes were associated with other amniote sex chromosomes. Hybridization of the same BACs onto multiple different chromosome pairs suggested transitions to sex chromosomes across amniotes. No BAC hybridization signals were found on HFR chromosomes. However, HFR diverged from HPL about 30 million years ago, possibly due to intrachromosomal rearrangements occurring in the HFR lineage. By contrast, heterochromatin likely reshuffled patterns between HPL and HFR, as observed from C-positive heterochromatin distribution. Six out of ten BACs showed partial homology with squamate reptile chromosome 2 (SR2) and snake Z and/or W sex chromosomes. The gecko lizard showed shared unrelated sex chromosomal linkages—the remnants of a super-sex chromosome. A large ancestral super-sex chromosome showed a correlation between SR2 and snake W sex chromosomes.
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Singchat, Worapong, Syed Farhan Ahmad, Nararat Laopichienpong, Aorarat Suntronpong, Thitipong Panthum, Darren K. Griffin i Kornsorn Srikulnath. "Snake W Sex Chromosome: The Shadow of Ancestral Amniote Super-Sex Chromosome". Cells 9, nr 11 (31.10.2020): 2386. http://dx.doi.org/10.3390/cells9112386.
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Heteromorphic sex chromosomes, particularly the ZZ/ZW sex chromosome system of birds and some reptiles, undergo evolutionary dynamics distinct from those of autosomes. The W sex chromosome is a unique karyological member of this heteromorphic pair, which has been extensively studied in snakes to explore the origin, evolution, and genetic diversity of amniote sex chromosomes. The snake W sex chromosome offers a fascinating model system to elucidate ancestral trajectories that have resulted in genetic divergence of amniote sex chromosomes. Although the principal mechanism driving evolution of the amniote sex chromosome remains obscure, an emerging hypothesis, supported by studies of W sex chromosomes of squamate reptiles and snakes, suggests that sex chromosomes share varied genomic blocks across several amniote lineages. This implies the possible split of an ancestral super-sex chromosome via chromosomal rearrangements. We review the major findings pertaining to sex chromosomal profiles in amniotes and discuss the evolution of an ancestral super-sex chromosome by collating recent evidence sourced mainly from the snake W sex chromosome analysis. We highlight the role of repeat-mediated sex chromosome conformation and present a genomic landscape of snake Z and W chromosomes, which reveals the relative abundance of major repeats, and identifies the expansion of certain transposable elements. The latest revolution in chromosomics, i.e., complete telomere-to-telomere assembly, offers mechanistic insights into the evolutionary origin of sex chromosomes.
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Pazhenkova, Elena A., i Vladimir A. Lukhtanov. "Whole-Genome Analysis Reveals the Dynamic Evolution of Holocentric Chromosomes in Satyrine Butterflies". Genes 14, nr 2 (8.02.2023): 437. http://dx.doi.org/10.3390/genes14020437.
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Butterfly chromosomes are holocentric, i.e., lacking a localized centromere. Potentially, this can lead to rapid karyotypic evolution through chromosome fissions and fusions, since fragmented chromosomes retain kinetic activity, while fused chromosomes are not dicentric. However, the actual mechanisms of butterfly genome evolution are poorly understood. Here, we analyzed chromosome-scale genome assemblies to identify structural rearrangements between karyotypes of satyrine butterfly species. For the species pair Erebia ligea–Maniola jurtina, sharing the ancestral diploid karyotype 2n = 56 + ZW, we demonstrate a high level of chromosomal macrosynteny and nine inversions separating these species. We show that the formation of a karyotype with a low number of chromosomes (2n = 36 + ZW) in Erebia aethiops was based on ten fusions, including one autosome–sex chromosome fusion, resulting in a neo-Z chromosome. We also detected inversions on the Z sex chromosome that were differentially fixed between the species. We conclude that chromosomal evolution is dynamic in the satyrines, even in the lineage that preserves the ancestral chromosome number. We hypothesize that the exceptional role of Z chromosomes in speciation may be further enhanced by inversions and sex chromosome–autosome fusions. We argue that not only fusions/fissions but also inversions are drivers of the holocentromere-mediated mode of chromosomal speciation.
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McAllister, Bryant F. "Sequence Differentiation Associated With an Inversion on the Neo-X Chromosome of Drosophila americana". Genetics 165, nr 3 (1.11.2003): 1317–28. http://dx.doi.org/10.1093/genetics/165.3.1317.
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Abstract Sex chromosomes originate from pairs of autosomes that acquire controlling genes in the sex-determining cascade. Universal mechanisms apparently influence the evolution of sex chromosomes, because this chromosomal pair is characteristically heteromorphic in a broad range of organisms. To examine the pattern of initial differentiation between sex chromosomes, sequence analyses were performed on a pair of newly formed sex chromosomes in Drosophila americana. This species has neo-sex chromosomes as a result of a centromeric fusion between the X chromosome and an autosome. Sequences were analyzed from the Alcohol dehydrogenase (Adh), big brain (bib), and timeless (tim) gene regions, which represent separate positions along this pair of neo-sex chromosomes. In the northwestern range of the species, the bib and Adh regions exhibit significant sequence differentiation for neo-X chromosomes relative to neo-Y chromosomes from the same geographic region and other chromosomal populations of D. americana. Furthermore, a nucleotide site defining a common haplotype in bib is shown to be associated with a paracentric inversion [In(4)ab] on the neo-X chromosome, and this inversion suppresses recombination between neo-X and neo-Y chromosomes. These observations are consistent with the inversion acting as a recombination modifier that suppresses exchange between these neo-sex chromosomes, as predicted by models of sex chromosome evolution.
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Gonzalez de la Rosa, Pablo Manuel, Marian Thomson, Urmi Trivedi, Alan Tracey, Sophie Tandonnet i Mark Blaxter. "A telomere-to-telomere assembly ofOscheius tipulaeand the evolution of rhabditid nematode chromosomes". G3 Genes|Genomes|Genetics 11, nr 1 (8.12.2020): 1–17. http://dx.doi.org/10.1093/g3journal/jkaa020.
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AbstractEukaryotic chromosomes have phylogenetic persistence. In many taxa, each chromosome has a single functional centromere with essential roles in spindle attachment and segregation. Fusion and fission can generate chromosomes with no or multiple centromeres, leading to genome instability. Groups with holocentric chromosomes (where centromeric function is distributed along each chromosome) might be expected to show karyotypic instability. This is generally not the case, and in Caenorhabditis elegans, it has been proposed that the role of maintenance of a stable karyotype has been transferred to the meiotic pairing centers, which are found at one end of each chromosome. Here, we explore the phylogenetic stability of nematode chromosomes using a new telomere-to-telomere assembly of the rhabditine nematode Oscheius tipulae generated from nanopore long reads. The 60-Mb O. tipulae genome is resolved into six chromosomal molecules. We find the evidence of specific chromatin diminution at all telomeres. Comparing this chromosomal O. tipulae assembly with chromosomal assemblies of diverse rhabditid nematodes, we identify seven ancestral chromosomal elements (Nigon elements) and present a model for the evolution of nematode chromosomes through rearrangement and fusion of these elements. We identify frequent fusion events involving NigonX, the element associated with the rhabditid X chromosome, and thus sex chromosome-associated gene sets differ markedly between species. Despite the karyotypic stability, gene order within chromosomes defined by Nigon elements is not conserved. Our model for nematode chromosome evolution provides a platform for investigation of the tensions between local genome rearrangement and karyotypic evolution in generating extant genome architectures.
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Surosky, R. T., i B. K. Tye. "Meiotic disjunction of homologs in Saccharomyces cerevisiae is directed by pairing and recombination of the chromosome arms but not by pairing of the centromeres." Genetics 119, nr 2 (1.06.1988): 273–87. http://dx.doi.org/10.1093/genetics/119.2.273.
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Abstract We explored the behavior of meiotic chromosomes in Saccharomyces cerevisiae by examining the effects of chromosomal rearrangements on the pattern of disjunction and recombination of chromosome III during meiosis. The segregation of deletion chromosomes lacking part or all (telocentric) of one arm was analyzed in the presence of one or two copies of a normal chromosome III. In strains containing one normal and any one deletion chromosome, the two chromosomes disjoined in most meioses. In strains with one normal chromosome and both a left and right arm telocentric chromosome, the two telocentrics preferentially disjoined from the normal chromosome. Homology on one arm was sufficient to direct chromosome disjunction, and two chromosomes could be directed to disjoin from a third. In strains containing one deletion chromosome and two normal chromosomes, the two normal chromosomes preferentially disjoined, but in 4-7% of the tetrads the normal chromosomes cosegregated, disjoining from the deletion chromosome. Recombination between the two normal chromosomes or between the deletion chromosome and a normal chromosome increased the probability that these chromosomes would disjoin, although cosegregation of recombinants was observed. Finally, we observed that a derivative of chromosome III in which the centromeric region was deleted and CEN5 was integrated at another site on the chromosome disjoined from a normal chromosome III with fidelity. These studies demonstrate that it is not pairing of the centromeres, but pairing and recombination along the arms of the homologs, that directs meiotic chromosome segregation.
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Yuan, Xiuyun, Siqi Yuan, Ya Liu, Yun Xia i Xiaomao Zeng. "Microsatellites mapping for non-model species with chromosomal rearrangement: a case study in the frog Quasipaa boulengeri (Anura: Dicroglossidae)". Genome 60, nr 8 (sierpień 2017): 707–11. http://dx.doi.org/10.1139/gen-2016-0200.
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Gene mapping is an important resource for understanding the evolution of genes and cytogenetics. Model species with a known genetic map or genome sequence allow for the selection of genetic markers on a desired chromosome, while it is hard to locate these markers on chromosomes of non-model species without such references. A frog species, Quasipaa boulengeri, shows chromosomal rearrangement polymorphisms, making itself a fascinating model for chromosomal speciation mediated by suppressed recombination. However, no markers have been located on its rearranged chromosomes. We present a complete protocol to map microsatellites based on mechanical microdissection and chromosome amplification techniques. Following this protocol, we mapped 71 microsatellites of Q. boulengeri at the chromosome level. In total, eight loci were assigned to rearranged chromosomes, and the other 63 loci might attach to other chromosomes. These microsatellites could be used to compare the gene flow and verify the chromosomal suppressed recombination hypothesis in Q. boulengeri. This integrated protocol could be effectively used to map genes to chromosomes for non-model species.
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SWEDAK, JULIA A. M., i ARTHUR FORER. "Sex-chromosome anaphase movements in crane-fly spermatocytes are coordinated: ultraviolet microbeam irradiation of one kinetochore of one sex chromosome blocks the movements of both sex chromosomes". Journal of Cell Science 88, nr 4 (1.11.1987): 441–52. http://dx.doi.org/10.1242/jcs.88.4.441.
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Sex chromosomes in crane-fly spermatocytes move polewards at anaphase after the autosomes have reached the poles. In Nephrotoma abbreviate the sex chromosomes are 8 μm long by 3.5 μm wide and have two orientations when they move: the long axis of the sex chromosome is either perpendicular or parallel to the spindle axis. We assume (1) that when a sex chromosome is perpendicular to the spindle axis it has a chromosomal spindle fibre to each pole, one from each kinetochore, as in other species; and (2) that when a sex chromosome is parallel to the spindle axis each kinetochore has spindle fibres to both poles, i.e. that the latter sex chromosomes are maloriented. We irradiated one kinetochore of one sex chromosome using an ultraviolet microbeam. When both sex chromosomes were normally oriented, irradiation of a single kinetochore permanently blocked movement of both sex chromosomes. Irradiation of non-kinetochore chromosomal regions or of spindle fibres did not block movement, or blocked movement only temporarily. We argue that ultraviolet irradiation of one kinetochore blocks movement of both sex chromosomes because of effects on a ‘signal’ system. The results were different when one sex chromosome was maloriented. Irradiation of one kinetochore of a maloriented sex chromosome did not block motion of either sex chromosome. On the other hand, irradiation of one kinetochore of a normally oriented sex chromosome permanently blocked motion of both that sex chromosome and the maloriented sex chromosome. We argue that for the signal system to allow the sex chromosomes to move to the pole each sex chromosome must have one spindle fibre to each pole.
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Uno, Yoshinobu, Chizuko Nishida, Chiyo Takagi, Takeshi Igawa, Naoto Ueno, Masayuki Sumida i Yoichi Matsuda. "Extraordinary Diversity in the Origins of Sex Chromosomes in Anurans Inferred from Comparative Gene Mapping". Cytogenetic and Genome Research 145, nr 3-4 (2015): 218–29. http://dx.doi.org/10.1159/000431211.
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Sex determination in frogs (anurans) is genetic and includes both male and female heterogamety. However, the origins of the sex chromosomes and their differentiation processes are poorly known. To investigate diversity in the origins of anuran sex chromosomes, we compared the chromosomal locations of sex-linked genes in 4 species: the African clawed frog (Xenopus laevis), the Western clawed frog (Silurana/X. tropicalis), the Japanese bell-ring frog (Buergeria buergeri), and the Japanese wrinkled frog (Rana rugosa). Comparative mapping data revealed that the sex chromosomes of X. laevis, X. tropicalis and R. rugosa are different chromosome pairs; however, the sex chromosomes of X. tropicalis and B. buergeri are homologous, although this may represent distinct evolutionary origins. We also examined the status of sex chromosomal differentiation in B. buergeri, which possesses heteromorphic ZW sex chromosomes, using comparative genomic hybridization and chromosome painting with DNA probes from the microdissected W chromosome. At least 3 rearrangement events have occurred in the proto-W chromosome: deletion of the nucleolus organizer region and a paracentric inversion followed by amplification of non-W-specific repetitive sequences.
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DUJARDIN, J. C., A. L. BAÑULS, J. P. DUJARDIN, J. AREVALO, M. TIBAYRENC i D. LE RAY. "Comparison of chromosome and isoenzyme polymorphism in geographical populations of Leishmania (Viannia) peruviana". Parasitology 117, nr 6 (grudzień 1998): 547–54. http://dx.doi.org/10.1017/s0031182098003357.
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Five chromosomes and 17 isoenzyme loci were analysed in 4 allopatric populations of Leishmania (Viannia) peruviana, and molecular distances calculated with 2 estimators, Chromosomal Size Difference Index and Jaccard Distance. Chromosome and isoenzyme data were in overall concordance: 13/30 isolates clustered similarly on the dendrograms constructed from the different estimators, and a significant correlation (P<0·001) was observed between the molecular distances calculated from the two sets of characters. This indicates an evolutionary association between chromosomal size polymorphism and isoenzymes. Chromosomes have a faster molecular clock than isoenzymes; twice as many genotypes were identified by chromosome analysis and significant size differences (for a total of up to 500 kb for 5 chromosomes together) were observed within a given zymodeme. Chromosomes most likely represent better indicators of genetic drift than isoenzymes, as suggested by the higher correlation between both estimators of chromosomal size-polymorphism and eco-geography. Some chromosomes might present an adaptive response to environmental variation.
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Kaback, David B., Dianna Barber, Jim Mahon, Jacque Lamb i Jerome You. "Chromosome Size-Dependent Control of Meiotic Reciprocal Recombination in Saccharomyces cerevisiae: The Role of Crossover Interference". Genetics 152, nr 4 (1.08.1999): 1475–86. http://dx.doi.org/10.1093/genetics/152.4.1475.
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Abstract In the yeast Saccharomyces cerevisiae, small chromosomes undergo meiotic reciprocal recombination (crossing over) at rates (centimorgans per kilobases) greater than those of large chromosomes, and recombination rates respond directly to changes in the total size of a chromosomal DNA molecule. This phenomenon, termed chromosome size-dependent control of meiotic reciprocal recombination, has been suggested to be important for ensuring that homologous chromosomes cross over during meiosis. The mechanism of this regulation was investigated by analyzing recombination in identical genetic intervals present on different size chromosomes. The results indicate that chromosome size-dependent control is due to different amounts of crossover interference. Large chromosomes have high levels of interference while small chromosomes have much lower levels of interference. A model for how crossover interference directly responds to chromosome size is presented. In addition, chromosome size-dependent control was shown to lower the frequency of homologous chromosomes that failed to undergo crossovers, suggesting that this control is an integral part of the mechanism for ensuring meiotic crossing over between homologous chromosomes.
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Neeru, Neeru, Anita Bhatnagar i Abhay Singh Yadav. "A study of constitutive heterochromatin and NOR banding in three species of Indian major carps from the State of Haryana, India". Journal of Applied and Natural Science 10, nr 2 (1.06.2018): 535–39. http://dx.doi.org/10.31018/jans.v10i2.1731.
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Cytogenetic survey of fishes becomes increasingly important to establish chromosomal relation between the teleosts, to have a glimpse of the relation between chromosomal evolution and differentiation of vertebrate species. In the present study, Chromosome banding studies was done in three species of carps i.e. Catla catla (Hamilton, 1822), Labeo rohita (Hamilton, 1822) and Cirrhinus mrigala (Hamilton, 1822). Diploid chromosome number 50 was observed in all 3 species of carps. The chromosomes of C. catla, L. rohita and C. mrigala showed constitutive heterochromatin at telomeric and centromeric regions of chromosomes. The Ag-NOR (Argyrophilic-Nucleolus Organizer Region) bands were observed on homologous chromosome pair number 11 in C. catla, 15th chromosome pair in L. rohita. In C. mrigala, the Ag- NOR staining elucidated the presence of darkly stained NORs on the terminal region of the long arms of one of the chromosome. Another homologue of this chromosome pair could not be localized due to scattering of chromosomes. The results depict that variation in ecological conditions with time due to human activities can not only affect the chromosomal number but also chromosomal morphology.
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Tamang, Sonam. "Principles and Applications of Fetal Chromosome Number and Structure Analysis". Sriwijaya Journal of Obstetrics and Gynecology 1, nr 2 (20.12.2023): 39–43. http://dx.doi.org/10.59345/sjog.v1i2.83.
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A crucial diagnostic technique employed in prenatal diagnosis is examining the quantity and arrangement of fetal chromosomes. The fundamental premise of this study is to determine the chromosomal count in the fetal cells and detect any genetic or chromosomal abnormalities that may be present. A total of 46 chromosomes are typically present in the human body, organized into 23 pairs. These pairs include one pair of sex chromosomes and 22 pairs of autosomal chromosomes. This study enables the identification of chromosomal abnormalities, such as trisomy (the presence of an additional chromosome) and monosomy (the absence of a chromosome), which can have an impact on the health of the fetus. In addition to determining the number of chromosomes, this examination can also detect structural chromosome abnormalities like translocations, deletions, and duplications, which might potentially affect the health of the fetus. This investigation's findings provide significant insights to both patients and clinicians, enabling them to make more informed choices about continuing the pregnancy and receiving appropriate medical attention if genetic abnormalities are detected. This study can also be utilized for the identification of particular genetic illnesses associated with specific gene mutations, thereby aiding in treatment strategizing and postnatal readiness.
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Eenennaam, A. L., J. D. Murray i J. F. Medrano. "Mitotic analysis of the North American white sturgeon, Acipenser transmontanus Richardson (Pisces, Acipenseridae), a fish with a very high chromosome number". Genome 41, nr 2 (1.04.1998): 266–71. http://dx.doi.org/10.1139/g98-018.
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The average chromosome number of the North American white sturgeon, Acipenser transmontanus Richardson, was found to be 271 ± 2.5 (ranging from 265 to 276). This number is significantly higher than previous estimates for this species. A representative karyotype was found to consist of 132 meta- and submeta-centric chromosomes, 44 acrocentric chromosomes, and 98 microchromosomes. An improved C-banding technique revealed variation (2-7) between animals in the number of entirely heterochromatic metacentric chromosomes. These heterochromatic chromosomes may represent supernumerary chromosomes. There was no cytogenetic evidence of a heteromorphic sex chromosome pair or any sex-related chromosomal polymorphism in either sex of this species.Key words: C-banding, fish, karyotype, supernumerary chromosomes, white sturgeon.
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Lo, Anthony W. I., Carl N. Sprung, Bijan Fouladi, Mehrdad Pedram, Laure Sabatier, Michelle Ricoul, Gloria E. Reynolds i John P. Murnane. "Chromosome Instability as a Result of Double-Strand Breaks near Telomeres in Mouse Embryonic Stem Cells". Molecular and Cellular Biology 22, nr 13 (1.07.2002): 4836–50. http://dx.doi.org/10.1128/mcb.22.13.4836-4850.2002.
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ABSTRACT Telomeres are essential for protecting the ends of chromosomes and preventing chromosome fusion. Telomere loss has been proposed to play an important role in the chromosomal rearrangements associated with tumorigenesis. To determine the relationship between telomere loss and chromosome instability in mammalian cells, we investigated the events resulting from the introduction of a double-strand break near a telomere with I-SceI endonuclease in mouse embryonic stem cells. The inactivation of a selectable marker gene adjacent to a telomere as a result of the I-SceI-induced double-strand break involved either the addition of a telomere at the site of the break or the formation of inverted repeats and large tandem duplications on the end of the chromosome. Nucleotide sequence analysis demonstrated large deletions and little or no complementarity at the recombination sites involved in the formation of the inverted repeats. The formation of inverted repeats was followed by a period of chromosome instability, characterized by amplification of the subtelomeric region, translocation of chromosomal fragments onto the end of the chromosome, and the formation of dicentric chromosomes. Despite this heterogeneity, the rearranged chromosomes eventually acquired telomeres and were stable in most of the cells in the population at the time of analysis. Our observations are consistent with a model in which broken chromosomes that do not regain a telomere undergo sister chromatid fusion involving nonhomologous end joining. Sister chromatid fusion is followed by chromosome instability resulting from breakage-fusion-bridge cycles involving the sister chromatids and rearrangements with other chromosomes. This process results in highly rearranged chromosomes that eventually become stable through the addition of a telomere onto the broken end. We have observed similar events after spontaneous telomere loss in a human tumor cell line, suggesting that chromosome instability resulting from telomere loss plays a role in chromosomal rearrangements associated with tumor cell progression.
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Hande, M. Prakash, Enrique Samper, Peter Lansdorp i María A. Blasco. "Telomere Length Dynamics and Chromosomal Instability in Cells Derived from Telomerase Null Mice". Journal of Cell Biology 144, nr 4 (22.02.1999): 589–601. http://dx.doi.org/10.1083/jcb.144.4.589.
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To study the effect of continued telomere shortening on chromosome stability, we have analyzed the telomere length of two individual chromosomes (chromosomes 2 and 11) in fibroblasts derived from wild-type mice and from mice lacking the mouse telomerase RNA (mTER) gene using quantitative fluorescence in situ hybridization. Telomere length at both chromosomes decreased with increasing generations of mTER−/− mice. At the 6th mouse generation, this telomere shortening resulted in significantly shorter chromosome 2 telomeres than the average telomere length of all chromosomes. Interestingly, the most frequent fusions found in mTER−/− cells were homologous fusions involving chromosome 2. Immortal cultures derived from the primary mTER−/− cells showed a dramatic accumulation of fusions and translocations, revealing that continued growth in the absence of telomerase is a potent inducer of chromosomal instability. Chromosomes 2 and 11 were frequently involved in these abnormalities suggesting that, in the absence of telomerase, chromosomal instability is determined in part by chromosome-specific telomere length. At various points during the growth of the immortal mTER−/− cells, telomere length was stabilized in a chromosome-specific man-ner. This telomere-maintenance in the absence of telomerase could provide the basis for the ability of mTER−/− cells to grow indefinitely and form tumors.
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Hanlon, Stacey, i R. Hawley. "B Chromosomes in the Drosophila Genus". Genes 9, nr 10 (27.09.2018): 470. http://dx.doi.org/10.3390/genes9100470.
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Our current knowledge of B chromosome biology has been augmented by an increase in the number and diversity of species observed to carry B chromosomes as well as the use of next-generation sequencing for B chromosome genomic analysis. Within the genus Drosophila, B chromosomes have been observed in a handful of species, but recently they were discovered in a single laboratory stock of Drosophila melanogaster. In this paper, we review the B chromosomes that have been identified within the Drosophila genus and pay special attention to those recently found in D. melanogaster. These newly-discovered B chromosomes have centromeres, telomeres, and a number of simple satellite repeats. They also appear to be entirely heterochromatic since next-generation sequencing of isolated B chromosomes did not detect sequences associated with known genic regions. We also summarize what effects the B chromosomes have been found to have on the A chromosomes. Lastly, we highlight some of the outstanding questions regarding B chromosome biology and discuss how studying B chromosomes in Drosophila melanogaster, which is a versatile model system with a wealth of genetic and genomic tools, may advance our understanding of the B chromosome’s unique biology.
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Li, J., D. L. Klindworth, F. Shireen, X. Cai, J. Hu i S. S. Xu. "Molecular characterization and chromosome-specific TRAP-marker development for Langdon durum D-genome disomic substitution lines". Genome 49, nr 12 (grudzień 2006): 1545–54. http://dx.doi.org/10.1139/g06-114.
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The aneuploid stocks of durum wheat ( Triticum turgidum L. subsp. durum (Desf.) Husnot) and common wheat ( T. aestivum L.) have been developed mainly in ‘Langdon’ (LDN) and ‘Chinese Spring’ (CS) cultivars, respectively. The LDN-CS D-genome chromosome disomic substitution (LDN-DS) lines, where a pair of CS D-genome chromosomes substitute for a corresponding homoeologous A- or B-genome chromosome pair of LDN, have been widely used to determine the chromosomal locations of genes in tetraploid wheat. The LDN-DS lines were originally developed by crossing CS nulli-tetrasomics with LDN, followed by 6 backcrosses with LDN. They have subsequently been improved with 5 additional backcrosses with LDN. The objectives of this study were to characterize a set of the 14 most recent LDN-DS lines and to develop chromosome-specific markers, using the newly developed TRAP (target region amplification polymorphism)-marker technique. A total of 307 polymorphic DNA fragments were amplified from LDN and CS, and 302 of them were assigned to individual chromosomes. Most of the markers (95.5%) were present on a single chromosome as chromosome-specific markers, but 4.5% of the markers mapped to 2 or more chromosomes. The number of markers per chromosome varied, from a low of 10 (chromosomes 1A and 6D) to a high of 24 (chromosome 3A). There was an average of 16.6, 16.6, and 15.9 markers per chromosome assigned to the A-, B-, and D-genome chromosomes, respectively, suggesting that TRAP markers were detected at a nearly equal frequency on the 3 genomes. A comparison of the source of the expressed sequence tags (ESTs), used to derive the fixed primers, with the chromosomal location of markers revealed that 15.5% of the TRAP markers were located on the same chromosomes as the ESTs used to generate the fixed primers. A fixed primer designed from an EST mapped on a chromosome or a homoeologous group amplified at least 1 fragment specific to that chromosome or group, suggesting that the fixed primers might generate markers from target regions. TRAP-marker analysis verified the retention of at least 13 pairs of A- or B-genome chromosomes from LDN and 1 pair of D-genome chromosomes from CS in each of the LDN-DS lines. The chromosome-specific markers developed in this study provide an identity for each of the chromosomes, and they will facilitate molecular and genetic characterization of the individual chromosomes, including genetic mapping and gene identification.
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Dzitsiuk, V., H. Bratytsia i T. Dyman. "Comparative analysis of karyotypes of Вovidae family from the evolutionary aspect". Agricultural Science and Practice 9, nr 1 (3.08.2022): 27–38. http://dx.doi.org/10.15407/agrisp9.01.027.
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Aim. The aim of the study was to analyze chromosome sets of specific species of agricultural animals of Bovidae family using the techniques of differentiated G- and Ag-banding of chromosomes and to demonstrate the role of their variability in the evolution. Methods. The culture of lymphocytes and chromosome preparations were pre- pared by the method of Moorhead et al (1960). The preparations of metaphase chromosomes were analyzed by the G-banding methods of Barch M J et al (1997) and by Ag-banding method of Zhu JJ et al (2019). The chromosomal aberrations were classified according to the recommendations of the International System for Chromosome No- menclature of Domestic Bovids (2001). The dendrogram of phylogenetic relations between mammalian species was built using “STATISTICA 6.1”. Results. The comparative study of the chromosomal sets of cattle Bos taurus, domestic sheep Ovis aries and river buffalo Bubalus bubalis bubalis was conducted using G- and Ag-banding methods. The homology of the structural organization of chromosomes and the evolutionary changes in karyotypes of Bovidae family were analyzed, highlighting their sex chromosomes and the chromosomes with specific local- ized groups of gene linkage. A considerable homology of chromosome sites was found in the representatives of the investigated species by the G-banding profiles. To study the phylogenetic interrelations, the index of the number of active nucleolus organizer regions (NOR) in the chromosomes during the metaphase stage was used. Conclu- sions. The comparison of the morphology of chromosomes of agricultural animals of Bovidae family, Bos taurus, Ovis aries, and Bubalus bubalis bubalis confirms the association between the homology of some chromosomal sites and the formation of metacentric chromosomes due to the linkage of acrocentric ones. The species-specific morphological differences in sex chromosomes of the investigated animals were found in terms of the length and presence of pericentric inversions. The phylogenetic relations between the species of Bovidae family demonstrate that the value of distances, determined based on the variability of the number of active NOR, reflects the degree of their phylogenetic similarity.
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Liang, Jiangtao, Simon M. Bondarenko, Igor V. Sharakhov i Maria V. Sharakhova. "Obtaining Polytene, Meiotic, and Mitotic Chromosomes from Mosquitoes for Cytogenetic Analysis". Cold Spring Harbor Protocols 2022, nr 12 (5.08.2022): pdb.prot107872. http://dx.doi.org/10.1101/pdb.prot107872.
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Chromosome visualization is a key step for developing cytogenetic maps and idiograms, analyzing inversion polymorphisms, and identifying mosquito species. Three types of chromosomes—polytene, mitotic, and meiotic—are used in cytogenetic studies of mosquitoes. Here, we describe a detailed method for obtaining high-quality polytene chromosome preparations from the salivary glands of larvae and the ovaries of females forAnophelesmosquitoes. We also describe how to obtain mitotic chromosomes from imaginal discs of fourth-instar larvae and meiotic chromosomes from the testes of male pupae for all mosquitoes. These chromosomes can be used for fluorescence in situ hybridization (FISH), a fundamental technique in cytogenetic research that is used for physical genome mapping, detecting chromosomal rearrangements, and studying chromosome organization.
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Lukhtanov, Vladimir A., Vlad Dincă, Magne Friberg, Jindra Šíchová, Martin Olofsson, Roger Vila, František Marec i Christer Wiklund. "Versatility of multivalent orientation, inverted meiosis, and rescued fitness in holocentric chromosomal hybrids". Proceedings of the National Academy of Sciences 115, nr 41 (28.09.2018): E9610—E9619. http://dx.doi.org/10.1073/pnas.1802610115.
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Chromosomal rearrangements (e.g., fusions/fissions) have the potential to drive speciation. However, their accumulation in a population is generally viewed as unlikely, because chromosomal heterozygosity should lead to meiotic problems and aneuploid gametes. Canonical meiosis involves segregation of homologous chromosomes in meiosis I and sister chromatid segregation during meiosis II. In organisms with holocentric chromosomes, which are characterized by kinetic activity distributed along almost the entire chromosome length, this order may be inverted depending on their metaphase I orientation. Here we analyzed the evolutionary role of this intrinsic versatility of holocentric chromosomes, which is not available to monocentric ones, by studying F1 to F4 hybrids between two chromosomal races of the Wood White butterfly (Leptidea sinapis), separated by at least 24 chromosomal fusions/fissions. We found that these chromosomal rearrangements resulted in multiple meiotic multivalents, and, contrary to the theoretical prediction, the hybrids displayed relatively high reproductive fitness (42% of that of the control lines) and regular behavior of meiotic chromosomes. In the hybrids, we also discovered inverted meiosis, in which the first and critical stage of chromosome number reduction was replaced by the less risky stage of sister chromatid separation. We hypothesize that the ability to invert the order of the main meiotic events facilitates proper chromosome segregation and hence rescues fertility and viability in chromosomal hybrids, potentially promoting dynamic karyotype evolution and chromosomal speciation.
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Cornforth, Michael N., Karin M. Greulich-Bode, Bradford D. Loucas, Javier Arsuaga, Mariel Vázquez, Rainer K. Sachs, Martina Brückner i in. "Chromosomes are predominantly located randomly with respect to each other in interphase human cells". Journal of Cell Biology 159, nr 2 (28.10.2002): 237–44. http://dx.doi.org/10.1083/jcb.200206009.
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To test quantitatively whether there are systematic chromosome–chromosome associations within human interphase nuclei, interchanges between all possible heterologous pairs of chromosomes were measured with 24-color whole-chromosome painting (multiplex FISH), after damage to interphase lymphocytes by sparsely ionizing radiation in vitro. An excess of interchanges for a specific chromosome pair would indicate spatial proximity between the chromosomes comprising that pair. The experimental design was such that quite small deviations from randomness (extra pairwise interchanges within a group of chromosomes) would be detectable. The only statistically significant chromosome cluster was a group of five chromosomes previously observed to be preferentially located near the center of the nucleus. However, quantitatively, the overall deviation from randomness within the whole genome was small. Thus, whereas some chromosome–chromosome associations are clearly present, at the whole-chromosomal level, the predominant overall pattern appears to be spatially random.
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Sajid, Atiqa, El-Nasir Lalani, Bo Chen, Teruo Hashimoto, Darren K. Griffin, Archana Bhartiya, George Thompson, Ian K. Robinson i Mohammed Yusuf. "Ultra-Structural Imaging Provides 3D Organization of 46 Chromosomes of a Human Lymphocyte Prophase Nucleus". International Journal of Molecular Sciences 22, nr 11 (1.06.2021): 5987. http://dx.doi.org/10.3390/ijms22115987.
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Three dimensional (3D) ultra-structural imaging is an important tool for unraveling the organizational structure of individual chromosomes at various stages of the cell cycle. Performing hitherto uninvestigated ultra-structural analysis of the human genome at prophase, we used serial block-face scanning electron microscopy (SBFSEM) to understand chromosomal architectural organization within 3D nuclear space. Acquired images allowed us to segment, reconstruct, and extract quantitative 3D structural information about the prophase nucleus and the preserved, intact individual chromosomes within it. Our data demonstrate that each chromosome can be identified with its homolog and classified into respective cytogenetic groups. Thereby, we present the first 3D karyotype built from the compact axial structure seen on the core of all prophase chromosomes. The chromosomes display parallel-aligned sister chromatids with familiar chromosome morphologies with no crossovers. Furthermore, the spatial positions of all 46 chromosomes revealed a pattern showing a gene density-based correlation and a neighborhood map of individual chromosomes based on their relative spatial positioning. A comprehensive picture of 3D chromosomal organization at the nanometer level in a single human lymphocyte cell is presented.
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Manicardi, G. C., D. C. Gautam, D. Bizzaro, E. Guicciardi, A. M. Bonvicini Pagliai i U. Bianchi. "Chromosome banding in aphids: G, C, AluI, and HaeIII banding patterns in Megoura viciae (Homoptera, Aphididae)". Genome 34, nr 4 (1.08.1991): 661–65. http://dx.doi.org/10.1139/g91-101.
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The holocentric mitotic chromosomes of Megoura viciae, a species that has been little studied cytogenetically to date, have been characterized by applying G, C, AluI, and HaeIII banding techniques. C bands have shown the best defined patterns, particularly on the X chromosome. This chromosome, on the other hand, behaved as the most reactive to the various treatments. Uncondensed, prometaphase X chromosomes showed a number of heterochromatic bands, interspersed among the euchromatin, which fused together during metaphase condensation. AluI and HaeIII treatments also produced reproducible banding patterns. These data permit an accurate identification of the X chromosome as well as of the autosomal pairs 1 and 2, and facilitate the construction of nonambiguous karyotypes. They will also stimulate studies on the organization of chromatin in holocentric, holokinetic chromosomes. Finally they could also promote research on chromosomal rearrangements that have occurred during the course of speciation and evolution of aphids, since these kinds of events may be significantly affected by the condition of chromosomal holocentrism.Key words: aphids, holocentric chromosomes, chromosome banding, heterochromatin.
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Albert, Patrice S., Tao Zhang, Kassandra Semrau, Jean-Marie Rouillard, Yu-Hsin Kao, Chung-Ju Rachel Wang, Tatiana V. Danilova, Jiming Jiang i James A. Birchler. "Whole-chromosome paints in maize reveal rearrangements, nuclear domains, and chromosomal relationships". Proceedings of the National Academy of Sciences 116, nr 5 (17.01.2019): 1679–85. http://dx.doi.org/10.1073/pnas.1813957116.
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Whole-chromosome painting probes were developed for each of the 10 chromosomes of maize by producing amplifiable libraries of unique sequences of oligonucleotides that can generate labeled probes through transcription reactions. These paints allow identification of individual homologous chromosomes for many applications as demonstrated in somatic root tip metaphase cells, in the pachytene stage of meiosis, and in interphase nuclei. Several chromosomal aberrations were examined as proof of concept for study of various rearrangements using probes that cover the entire chromosome and that label diverse varieties. The relationship of the supernumerary B chromosome and the normal chromosomes was examined with the finding that there is no detectable homology between any of the normal A chromosomes and the B chromosome. Combined with other chromosome-labeling techniques, a complete set of whole-chromosome oligonucleotide paints lays the foundation for future studies of the structure, organization, and evolution of genomes.
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Asmaa Amer Almukhtar, Amal Mohammed Ali i Noor Hashim Ismail. "Cytogenetic study for Iraqi patients with epilepsy". Iraqi Journal of Cancer and Medical Genetics 16, nr 1 (1.06.2023): 7–13. http://dx.doi.org/10.29409/ijcmg.v16i1.285.
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The current study was conducted with the aim of identifying the chromosomal changes that associated with epilepsy Iraqi patients. Chromosomal analysis was carried on for 37 of a number of epilepsy patients exclusively for cases of idiopathic epilepsy (unknown cause)after excluding the symptomatic epilepsy (known causes) range age from 2-51 years. Only five cases showed chromosomal changes associated with epilepsy cases, their ages ranged from 2-30 years, while the rest of the patients had normal karyotype. The chromosomes were prepared using the GTG band with average of 25-30 cells was examined for each person. The chromosomal changes that associated with epilepsy cases, ranged from the presence of a number of derivative chromosomes, inversion, additions, deletions, chromatid fractures, and the premature centromere division (PCD).Finally the recurrence of aberrations in some chromosomes (more than one defect associated with the same chromosome). Which may indicate that these chromosomes carry more than one fragile site sin same chromosome. During questionnaire there were other symptoms associated with epilepsy which has been mentioned to them in the study.
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Gottesdiener, K., J. Garciá-Anoveros, M. G. Lee i L. H. Van der Ploeg. "Chromosome organization of the protozoan Trypanosoma brucei". Molecular and Cellular Biology 10, nr 11 (listopad 1990): 6079–83. http://dx.doi.org/10.1128/mcb.10.11.6079-6083.1990.
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The genome of the protozoan Trypanosoma brucei is known to be diploid. Karyotype analysis has, however, failed to identify homologous chromosomes. Having refined the technique for separating trypanosome chromosomes (L. H. T. Van der Ploeg, C. L. Smith, R. I. Polvere, and K. Gottesdiener, Nucleic Acids Res. 17:3217-3227, 1989), we can now provide evidence for the presence of homologous chromosomes. By determining the chromosomal location of different genetic markers, most of the chromosomes (14, excluding the minichromosomes), could be organized into seven chromosome pairs. In most instances, the putative homologs of a pair differed in size by about 20%. Restriction enzyme analysis of chromosome-sized DNA showed that these chromosome pairs contained large stretches of homologous DNA sequences. From these data, we infer that the chromosome pairs represent homologs. The identification of homologous chromosomes gives valuable insight into the organization of the trypanosome genome, will facilitate the genetic analysis of T. brucei, and suggests the presence of haploid gametes.
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Gottesdiener, K., J. Garciá-Anoveros, M. G. Lee i L. H. Van der Ploeg. "Chromosome organization of the protozoan Trypanosoma brucei." Molecular and Cellular Biology 10, nr 11 (listopad 1990): 6079–83. http://dx.doi.org/10.1128/mcb.10.11.6079.
Pełny tekst źródłaStreszczenie:
The genome of the protozoan Trypanosoma brucei is known to be diploid. Karyotype analysis has, however, failed to identify homologous chromosomes. Having refined the technique for separating trypanosome chromosomes (L. H. T. Van der Ploeg, C. L. Smith, R. I. Polvere, and K. Gottesdiener, Nucleic Acids Res. 17:3217-3227, 1989), we can now provide evidence for the presence of homologous chromosomes. By determining the chromosomal location of different genetic markers, most of the chromosomes (14, excluding the minichromosomes), could be organized into seven chromosome pairs. In most instances, the putative homologs of a pair differed in size by about 20%. Restriction enzyme analysis of chromosome-sized DNA showed that these chromosome pairs contained large stretches of homologous DNA sequences. From these data, we infer that the chromosome pairs represent homologs. The identification of homologous chromosomes gives valuable insight into the organization of the trypanosome genome, will facilitate the genetic analysis of T. brucei, and suggests the presence of haploid gametes.
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Willhoeft, Ute, Jutta Mueller-Navia i Gerald Franz. "Analysis of the sex chromosomes of the Mediterranean fruit fly by microdissected DNA probes". Genome 41, nr 1 (1.02.1998): 74–78. http://dx.doi.org/10.1139/g97-102.
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In the Mediterranean fruit fly, Ceratitis capitata, the sex-determining region maps to the long arm of the Y chromosome. DNA from this region of the Y chromosome and, for comparison, from the tip of the long arm of the X chromosome, was isolated by microdissection and amplified by degenerate oligonucleotide primer PCR (DOP-PCR). FISH of the Y-chromosomal microdissection products medY1-medY5 to mitotic chromosomes revealed hybridization signals on most of the long arm of the Y chromosome, including the male-determining region, and on the long arm of the X chromosome, as well as weaker signals on the autosomes, some of which were located in the heterochromatin next to the centromeres. The X-chromosomal microdissected probe medX1 revealed strong signals on the sex chromosomes and randomly distributed signals on the autosomes. Chromosomal in situ suppression hybridization indicates that the Y chromosome contains considerable amounts of Y-enriched and Y-specific sequences and that X-enriched sequences are present on the long arm of the X chromosome. The microdissected probes medY1, medY2, and medX1 hybridize to the sex chromosomes of two closely related species,Ceratitis rosa and Trirhithrum coffeae.
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de Vos, Jurriaan M., Hannah Augustijnen, Livio Bätscher i Kay Lucek. "Speciation through chromosomal fusion and fission in Lepidoptera". Philosophical Transactions of the Royal Society B: Biological Sciences 375, nr 1806 (13.07.2020): 20190539. http://dx.doi.org/10.1098/rstb.2019.0539.
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Changes in chromosome numbers may strongly affect reproductive barriers, because individuals heterozygous for distinct karyotypes are typically expected to be at least partially sterile or to show reduced recombination. Therefore, several classic speciation models are based on chromosomal changes. One import mechanism generating variation in chromosome numbers is fusion and fission of existing chromosomes, which is particularly likely in species with holocentric chromosomes, i.e. chromosomes that lack a single centromere. Holocentric chromosomes evolved repeatedly across the tree of life, including in Lepidoptera . Although changes in chromosome numbers are hypothesized to be an important driver of the spectacular diversification of Lepidoptera, comparative studies across the order are lacking. We performed the first comprehensive literature survey of karyotypes for Lepidoptera species since the 1970s and tested if, and how, chromosomal variation might affect speciation. Even though a meta-analysis of karyological differences between closely related taxa did not reveal an effect on the degree of reproductive isolation, phylogenetic diversification rate analyses across the 16 best-covered genera indicated a strong, positive association of rates of chromosome number evolution and speciation. These findings suggest a macroevolutionary impact of varying chromosome numbers in Lepidoptera and likely apply to other taxonomic groups, especially to those with holocentric chromosomes. This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers’.
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Konerat, Jocicléia Thums, Vanessa Bueno, Lucas Baumgartner, Isabel Cristina Martins-Santos i Vladimir Pavan Margarido. "B chromosome and NORs polymorphism in Callichthys callichthys (Linnaeus, 1758) (Siluriformes: Callichthyidae) from upper Paraná River, Brazil". Neotropical Ichthyology 12, nr 3 (23.06.2014): 603–9. http://dx.doi.org/10.1590/1982-0224-20130189.
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B chromosomes are extra chromosomes from the normal chromosomal set, found in different organisms, highlighting their presence on the group of fishes. Callichthys callichthys from the upper Paraná River has a diploid number of 56 chromosomes (26 m-sm + 30 st-a) for both sexes, with the presence of a sporadically acrocentric B chromosome. Moreover, one individual presented a diploid number of 57 chromosomes, with the presence of a morphologically ill-defined acrocentric B chromosome in all analyzed cells. The physical mapping of 5S and 18S rDNA shows multiple 5S rDNA sites and only one pair of chromosomes with 18S sites in C. callichthys, except for two individuals. These two individuals presented a third chromosome bearing NORs (Ag-staining and 18S rDNA) where 5S and 18S rDNA genes are syntenic, differing only in position. The dispersion of the 18S rDNA genes from the main st-achromosome pair 25 to one of the chromosomes from the m-sm pair 4 would have originated two variant individuals, one of which with the ill-defined acrocentric B chromosome. Mechanisms to justify the suggested hypothesis about this B chromosome origin are discussed in the present study.
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McAllister, Bryant F., i Brian Charlesworth. "Reduced Sequence Variability on the NeoY Chromosome of Drosophila americana americana". Genetics 153, nr 1 (1.09.1999): 221–33. http://dx.doi.org/10.1093/genetics/153.1.221.
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Abstract Sex chromosomes are generally morphologically and functionally distinct, but the evolutionary forces that cause this differentiation are poorly understood. Drosophila americana americana was used in this study to examine one aspect of sex chromosome evolution, the degeneration of nonrecombining Y chromosomes. The primary X chromosome of D. a. americana is fused with a chromosomal element that was ancestrally an autosome, causing this homologous chromosomal pair to segregate with the sex chromosomes. Sequence variation at the Alcohol Dehydrogenase (Adh) gene was used to determine the pattern of nucleotide variation on the neo-sex chromosomes in natural populations. Sequences of Adh were obtained for neo-X and neo-Y chromosomes of D. a. americana, and for Adh of D. a. texana, in which it is autosomal. No significant sequence differentiation is present between the neo-X and neo-Y chromosomes of D. a. americana or the autosomes of D. a. texana. There is a significantly lower level of sequence diversity on the neo-Y chromosome relative to the neo-X in D. a. americana. This reduction in variability on the neo-Y does not appear to have resulted from a selective sweep. Coalescent simulations of the evolutionary transition of an autosome into a Y chromosome indicate there may be a low level of recombination between the neo-X and neo-Y alleles of Adh and that the effective population size of this chromosome may have been reduced below the expected value of 25% of the autosomal effective size, possibly because of the effects of background selection or sexual selection.
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Kuniyasu, Kinue, Kenji Iemura i Kozo Tanaka. "Delayed Chromosome Alignment to the Spindle Equator Increases the Rate of Chromosome Missegregation in Cancer Cell Lines". Biomolecules 9, nr 1 (28.12.2018): 10. http://dx.doi.org/10.3390/biom9010010.
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For appropriate chromosome segregation, kinetochores on sister chromatids have to attach to microtubules from opposite spindle poles (bi-orientation). Chromosome alignment at the spindle equator, referred to as congression, can occur through the attachment of kinetochores to the lateral surface of spindle microtubules, facilitating bi-orientation establishment. However, the contribution of this phenomenon to mitotic fidelity has not been clarified yet. Here, we addressed whether delayed chromosome alignment to the spindle equator increases the rate of chromosome missegregation. Cancer cell lines depleted of Kid, a chromokinesin involved in chromosome congression, showed chromosome alignment with a slight delay, and increased frequency of lagging chromosomes. Delayed chromosome alignment concomitant with an increased rate of lagging chromosomes was also seen in cells depleted of kinesin family member 4A (KIF4A), another chromokinesin. Cells that underwent chromosome missegregation took relatively longer time to align chromosomes in both control and Kid/KIF4A-depleted cells. Tracking of late-aligning chromosomes showed that they exhibit a higher rate of lagging chromosomes. Intriguingly, the metaphase of cells that underwent chromosome missegregation was shortened, and delaying anaphase onset ameliorated the increased chromosome missegregation. These data suggest that late-aligning chromosomes do not have sufficient time to establish bi-orientation, leading to chromosome missegregation. Our data imply that delayed chromosome alignment is not only a consequence, but also a cause of defective bi-orientation establishment, which can lead to chromosomal instability in cells without severe mitotic defects.
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Milani, Diogo, Vanessa Bardella, Ana Ferretti, Octavio Palacios-Gimenez, Adriana Melo, Rita Moura, Vilma Loreto, Hojun Song i Diogo Cabral-de-Mello. "Satellite DNAs Unveil Clues about the Ancestry and Composition of B Chromosomes in Three Grasshopper Species". Genes 9, nr 11 (26.10.2018): 523. http://dx.doi.org/10.3390/genes9110523.
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Supernumerary (B) chromosomes are dispensable genomic elements occurring frequently among grasshoppers. Most B chromosomes are enriched with repetitive DNAs, including satellite DNAs (satDNAs) that could be implicated in their evolution. Although studied in some species, the specific ancestry of B chromosomes is difficult to ascertain and it was determined in only a few examples. Here we used bioinformatics and cytogenetics to characterize the composition and putative ancestry of B chromosomes in three grasshopper species, Rhammatocerus brasiliensis, Schistocerca rubiginosa, and Xyleus discoideus angulatus. Using the RepeatExplorer pipeline we searched for the most abundant satDNAs in Illumina sequenced reads, and then we generated probes used in fluorescent in situ hybridization (FISH) to determine chromosomal position. We used this information to infer ancestry and the events that likely occurred at the origin of B chromosomes. We found twelve, nine, and eighteen satDNA families in the genomes of R. brasiliensis, S. rubiginosa, and X. d. angulatus, respectively. Some satDNAs revealed clustered organization on A and B chromosomes varying in number of sites and position along chromosomes. We did not find specific satDNA occurring in the B chromosome. The satDNAs shared among A and B chromosomes support the idea of putative intraspecific ancestry from small autosomes in the three species, i.e., pair S11 in R. brasiliensis, pair S9 in S. rubiginosa, and pair S10 in X. d. angulatus. The possibility of involvement of other chromosomal pairs in B chromosome origin is also hypothesized. Finally, we discussed particular aspects in composition, origin, and evolution of the B chromosome for each species.
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Malimpensa, Geovana C., Josiane B. Traldi, Danyelle Toyama, Flávio Henrique-Silva, Marcelo R. Vicari i Orlando Moreira-Filho. "Chromosomal Mapping of Repeat DNA in Bergiaria westermanni (Pimelodidae, Siluriformes): Localization of 45S rDNA in B Chromosomes". Cytogenetic and Genome Research 154, nr 2 (2018): 99–106. http://dx.doi.org/10.1159/000487652.
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The occurrence of repetitive DNA in autosomes and B chromosomes of Bergiaria westermanni was examined using conventional and molecular cytogenetic techniques. This species exhibited 2n = 56 chromosomes, with intra- and interindividual variation in the number of heterochromatic B chromosomes (from 0 to 4). The 5S rDNA was localized in pairs 1 and 5, and histone probes (H1, H3, and H4) and U2 small nuclear RNA were syntenic with 5S rDNA in pair 5. Histone sequences were also located in chromosome pair 14. The (GATA)n sequence was dispersed throughout the autosomes and B chromosomes, with clusters (microsatellite accumulation) in some chromosome regions. The telomeric probe revealed no signs of chromosomal rearrangements in the genome of B. westermanni. The 45S rDNA sites were detected in the terminal region of pair 27; these sites corresponded to a GC-rich heterochromatin block. In addition, 3 of the 4 B chromosomes also contained 45S rDNA copies. Silver nitrate staining in interphase nuclei provided indirect evidence of the expression of these rRNA genes in B chromosomes, indicating the probable origin of these elements. This report shows plasticity in the chromosomal localization of repeat DNA in B. westermanni and features a discussion of genomic diversification.
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Rovatsos, Michail, Juan Alberto Marchal, Eva Giagia-Athanasopoulou i Antonio Sánchez. "Molecular Composition of Heterochromatin and Its Contribution to Chromosome Variation in the Microtus thomasi/Microtus atticus Species Complex". Genes 12, nr 6 (25.05.2021): 807. http://dx.doi.org/10.3390/genes12060807.
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The voles of the Microtus thomasi/M. atticus species complex demonstrate a remarkable variability in diploid chromosomal number (2n = 38–44 chromosomes) and sex chromosome morphology. In the current study, we examined by in situ hybridization the topology of four satellite DNA motifs (Msat-160, Mth-Alu900, Mth-Alu2.2, TTAGGG telomeric sequences) and two transposons (LINE, SINE) on the karyotypes of nine chromosome races (i.e., populations with unique cytogenetic traits) of Microtus thomasi, and two chromosomal races of M. atticus. According to the topology of the repetitive DNA motifs, we were able to identify six types of biarmed chromosomes formed from either Robertsonian or/and tandem fusions. In addition, we identified 14 X chromosome variants and 12 Y chromosome variants, and we were able to reconstruct their evolutionary relations, caused mainly by distinct mechanisms of amplification of repetitive DNA elements, including the telomeric sequences. Our study used the model of the Microtus thomasi/M. atticus species complex to explore how repetitive centromeric content can alter from chromosomal rearrangements and can shape the morphology of sex chromosomes, resulting in extensive inter-species cytogenetic variability.
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Schmid, Michael, i Claus Steinlein. "The Hypermethylated Regions in Avian Chromosomes". Cytogenetic and Genome Research 151, nr 4 (2017): 216–27. http://dx.doi.org/10.1159/000464268.
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Chromosomal locations and amounts of 5-methylcytosine-rich chromosome regions were detected in the karyotypes of 13 bird species by indirect immunofluorescence using a monoclonal anti-5-methylcytosine antibody. These species belong to 7 orders and 10 families of modern (Neognathae) and primitive (Palaeognathae) birds and are characterized by macro- and microchromosomes as well as ZW sex chromosomes. In all 13 species, the hypermethylated chromosome segments are confined to constitutive heterochromatin. The chromosomal locations of hypermethylated DNA regions in the karyotypes are constant and species-specific. There is no general rule with regard to the distribution of these hypermethylated chromosome regions in the genomes of birds. In most instances, hypermethylated segments are located in the centromeric regions of chromosomes, but in the sex chromosomes, these can also be found in telomeric and interstitial postitions. In most of the species studied, the centromeric heterochromatin in many, if not all, of the microchromosomes is hypermethylated. However, in one species, the only detectable hypermethylated heterochromatic regions are located in one pair of macroautosomes and in the Z sex chromosome, but none of the microchromosomes contains visible quantities of 5-methylcytosine. The analysis of 5-methylcytosine-rich chromosome regions can be very helpful for the comparative cytogenetics of closely related species or subspecies. It also reflects the dynamic evolutionary process operating in the highly repetitive DNA of eukaryotic chromosomes.
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Li, Jianyong, Bing Xiao, Lijuan Chen, Yu Zhu, Wei Xu i Hairong Qiu. "Whole Chromosome Painting and Multiplex Fluorescence In Situ Hybridization in Detecting Complex Chromosomal Aberrations in Myelodysplastic Syndromes." Blood 108, nr 11 (16.11.2006): 4853. http://dx.doi.org/10.1182/blood.v108.11.4853.4853.
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Abstract Objective To explore the value of the technique of whole chromosome painting (WCP) and multiplex fluorescence in situ hybridization (M-FISH) in the detection of complex chromosomal aberrations (CCAs) of myelodysplastic syndromes (MDS). Methods M-FISH was used in seven MDS patients with CCAs detected by R-banding technique to refine CCAs, and to identify cryptic translocations and characterization of marker chromosomes. Dual-color WCP procedures were further performed in 7 cases to confirm some rearrangements detected by M-FISH. Results In all cases, M-FISH confirmed all results of R-banding.The composition and origin of 6 kinds of marker chromosomes, 9 kinds of chromosomes with additional material undetermined and 5 kinds of derivative chromosomes undefined by CC were defined after M-FISH analysis; 4 kinds of cryptic translocations overlooked by CC were found on derivative chromosomes and previously normal appearing chromosomes. In addition, M-FISH revealed some nonrandom aberrations: aberrations involving chromosome 17 (5/7) and -5/5q- (4/7) were the two most frequent aberrations. Fluorescence flaring is a main factor leading to misinterpretations. Some misclassified and missed chromosomal aberrations by M-FISH were corrected by WCP. Conclusions M-FISH is a powerful molecular cytogenetic tool in clarification of CCAs. Complementary WCP helped us identify misclassified and missed chromosomal aberrations by M-FISH. CC in combination with molecular cytogenetic techniques M-FISH and WCP can unravel complex chromosomal aberrations more precisely.
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Li, Ziang, Yunfei Bi, Xing Wang, Yunzhu Wang, Shuqiong Yang, Zhentao Zhang, Jinfeng Chen i Qunfeng Lou. "Chromosome identification in Cucumis anguria revealed by cross-species single-copy gene FISH". Genome 61, nr 6 (czerwiec 2018): 397–404. http://dx.doi.org/10.1139/gen-2017-0235.
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Cucumis anguria is a potential genetic resource for improving crops of the genus Cucumis, owing to its broad-spectrum resistance. However, few cytogenetic studies on C. anguria have been reported because of its small metaphase chromosomes and the scarcity of distinguished chromosomal landmarks. In this study, 14 single-copy genes from cucumber and rDNAs were used as probes for FISH to identify the individual chromosomes of C. anguria. The distinctive signal distribution patterns of the probes allowed us to distinguish each chromosome of C. anguria (A01–A12). Further, detailed chromosome characteristics were obtained through pachytene chromosome FISH. The lengths of pachytene chromosomes varied from 54.80 to 143.41 μm. The proportion of heterochromatin regions varied from 13.56% to 63.86%. Finally, the chromosomal homeologous relationship between C. anguria and cucumber (C1–C7) was analyzed. The results showed that A06 + A09, A03 + A12, A02 + A04, and A01 + A11 were homeologs of C1, C2, C3, and C6, respectively. Furthemore, chromosomes A08, A10, and A05 were homeologs of C4, C5, and C7, respectively. Chromosome identification and homeologous relationship analysis between C. anguria and cucumber lay the foundation for further research of genome structure evolution in species of Cucumis.
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Rovatsos, Michail T., Juan A. Marchal, Ismael Romero-Fernández, Maria Arroyo, Eva B. Athanasopoulou i Antonio Sánchez. "Extensive Sex Chromosome Polymorphism of Microtus thomasi/Microtus atticus Species Complex Associated with Cryptic Chromosomal Rearrangements and Independent Accumulation of Heterochromatin". Cytogenetic and Genome Research 151, nr 4 (2017): 198–207. http://dx.doi.org/10.1159/000477114.
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The sibling species Microtus thomasi and M. atticus represent probably the highest karyotypic diversity within the genus Microtus and are an interesting model for chromosomal evolution studies. In addition to variation in autosomes, they show a high intraspecific variation in the size and morphology of both sex chromosomes. We analyzed individuals with different sex chromosome constitutions using 3 painting probes, 2 from Y chromosome variants and 1 from the small arm of the submetacentric X chromosome. Our comparative painting approach uncovered 12 variants of Y and 14 variants of X chromosomes, which demonstrates that the polymorphism of sex chromosomes is substantially larger than previously reported. We suggest that 2 main processes are responsible for this sex chromosome polymorphism: change of morphology from acrocentric to submetacentric or metacentric chromosomes and increase in size due to accumulation of repetitive DNA sequences, generating heterochromatic blocks. Strong genetic drift in small and fragmented populations of these 2 species could be related to the origin and maintenance of the large polymorphism of sex chromosomes. We proposed that a similar polymorphism variation combined with random drift fixing the biggest sex chromosomes could have occurred in the origin of some of the actual Microtus species with giant sex chromosomes.
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Hirano, T., i T. J. Mitchison. "Topoisomerase II does not play a scaffolding role in the organization of mitotic chromosomes assembled in Xenopus egg extracts." Journal of Cell Biology 120, nr 3 (1.02.1993): 601–12. http://dx.doi.org/10.1083/jcb.120.3.601.
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We have investigated the role of topoisomerase II (topo II) in mitotic chromosome assembly and organization in vitro using Xenopus egg extracts. When sperm chromatin was incubated with mitotic extracts, the highly compact chromatin rapidly swelled and concomitantly underwent local condensation. Further incubation induced the formation of entangled thin chromatin fibers that eventually resolved into highly condensed individual chromosomes. This in vitro system made it possible to manipulate mitotic chromosomes in their assembly condition without any isolation or stabilization steps. Two complementary approaches, immunodepletion and antibody blocking, demonstrated that topo II activity is required for chromosome assembly and condensation. Once condensation was completed, however, blocking of topo II activity had little effect on the chromosome morphology. Immunofluorescent studies showed that topo II was uniformly distributed throughout the condensed chromosomes and was not restricted to the chromosomal axis. Surprisingly, all detectable topo II molecules were easily extracted from the chromosomes under mild conditions where the shape of chromosomes was well preserved. Our results show that topo II is essential for mitotic chromosome assembly, but does not play a scaffolding role in the structural maintenance of chromosomes assembled in vitro. We also present evidence that changes of DNA topology affect the distribution of topo II in mitotic chromosomes in our system.
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Vernizzi, Luisa, i Christian F. Lehner. "Dispersive forces and resisting spot welds by alternative homolog conjunction govern chromosome shape in Drosophila spermatocytes during prophase I". PLOS Genetics 18, nr 7 (27.07.2022): e1010327. http://dx.doi.org/10.1371/journal.pgen.1010327.
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The bivalent chromosomes that are generated during prophase of meiosis I comprise a pair of homologous chromosomes. Homolog pairing during prophase I must include mechanisms that avoid or eliminate entanglements between non-homologous chromosomes. In Drosophila spermatocytes, non-homologous associations are disrupted by chromosome territory formation, while linkages between homologous chromosomes are maintained by special conjunction proteins. These proteins function as alternative for crossovers that link homologs during canonical meiosis but are absent during the achiasmate Drosophila male meiosis. How and where within bivalents the alternative homolog conjunction proteins function is still poorly understood. To clarify the rules that govern territory formation and alternative homolog conjunction, we have analyzed spermatocytes with chromosomal aberrations. We examined territory formation after acute chromosome cleavage by Cas9, targeted to the dodeca satellite adjacent to the centromere of chromosome 3 specifically in spermatocytes. Moreover, we studied territory organization, as well as the eventual orientation of chromosomes during meiosis I, in spermatocytes with stable structural aberrations, including heterozygous reciprocal autosomal translocations. Our observations indicate that alternative homolog conjunction is applied in a spatially confined manner. Comparable to crossovers, only a single conjunction spot per chromosome arm appears to be applied usually. These conjunction spots resist separation by the dispersing forces that drive apart homologous pericentromeric heterochromatin and embedded centromeres within territories, as well as the distinct chromosomal entities into peripheral, maximally separated territories within the spermatocyte nucleus.
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Drouin, Régen, i Claude-Lise Richer. "High-resolution R-banding at the 1250-band level. II. Schematic representation and nomenclature of human RBG-banded chromosomes". Genome 32, nr 3 (1.06.1989): 425–39. http://dx.doi.org/10.1139/g89-466.
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Detailed characterization of the RBG-banding pattern at the 1250-band level has been done after thymidine synchronization and block release with 5-bromo-2′-deoxyuridine (BrdU), which induces chromosome elongation and improves definition of chromosomal bands. Optimal conditions for the incorporation of BrdU and the use of the FPG (fluorochrome–photolysis–Giemsa) technique produced excellent band separation and band contrast even in highly elongated prophase chromosomes. Moreover, we did not observe lateral asymmetry in C-banded regions. The schematic representation of these elongated chromosomes in the 1250-band range per haploid set was prepared showing the relative position, the specific size, and the characteristic staining intensity for each band. To this idiogram was extended the International Standard Cytogenetic Nomenclature. This realistic idiogram should help in the preparation of R-banded prophase karyotypes and in the identification and localization of chromosomal rearrangements. Because differences exist between RBG and RHG bands, a brief comparative description of each RBG-banded chromosome is included. Moreover, a minute analysis of the banding pattern revealed that various parts of chromosomes contract differently. We also observed the presence of R-positive bands in heterochromatic regions of the short arms of the acrocentrics, and of chromosomes 1, 9, 16, and Y.Key words: high-resolution chromosome banding, R-banding, idiogram, dynamic bandings, prophase chromosomes, chromosome banding by BrdU incorporation.
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Csonka, E., I. Cserpan, K. Fodor, G. Hollo, R. Katona, J. Kereso, T. Praznovszky i in. "Novel generation of human satellite DNA-based artificial chromosomes in mammalian cells". Journal of Cell Science 113, nr 18 (15.09.2000): 3207–16. http://dx.doi.org/10.1242/jcs.113.18.3207.
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An in vivo approach has been developed for generation of artificial chromosomes, based on the induction of intrinsic, large-scale amplification mechanisms of mammalian cells. Here, we describe the successful generation of prototype human satellite DNA-based artificial chromosomes via amplification-dependent de novo chromosome formations induced by integration of exogenous DNA sequences into the centromeric/rDNA regions of human acrocentric chromosomes. Subclones with mitotically stable de novo chromosomes were established, which allowed the initial characterization and purification of these artificial chromosomes. Because of the low complexity of their DNA content, they may serve as a useful tool to study the structure and function of higher eukaryotic chromosomes. Human satellite DNA-based artificial chromosomes containing amplified satellite DNA, rDNA, and exogenous DNA sequences were heterochromatic, however, they provided a suitable chromosomal environment for the expression of the integrated exogenous genetic material. We demonstrate that induced de novo chromosome formation is a reproducible and effective methodology in generating artificial chromosomes from predictable sequences of different mammalian species. Satellite DNA-based artificial chromosomes formed by induced large-scale amplifications on the short arm of human acrocentric chromosomes may become safe or low risk vectors in gene therapy.
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Pande, Shailesh, Mani Bhushan, Anurita Pais, Gauri Pradhan, Chaitali Kadam i Sunmeet Matkar. "Immunodeficiency, centromeric heterochromatin instability of chromosomes 1, 9, and 16, and facial anomalies: the ICF syndrome". International Journal of Contemporary Pediatrics 4, nr 4 (21.06.2017): 1545. http://dx.doi.org/10.18203/2349-3291.ijcp20172706.
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Instability of the heterochromatic centromeric regions of chromosomes 1 associated with immunodeficiency was found in a 3 and half months old girl. The case was referred to Department of Genetics, Global Reference Laboratory, Metropolis Healthcare Ltd, Mumbai with the suspicion of Downs Syndrome for chromosomal karyotyping. This patient had facial anomalies in addition to combined immunodeficiency and chromosomal instability. Stretching of the heterochromatic centromeric regions of chromosomes 1 and homologous and non-homologous associations of these regions were the most common cytogenetic findings in this patient. Multi-branched configurations and whole arm deletions of chromosomes 1 were also found. Comparing clinical and chromosomal data we conclude that the patient was suffering from immunodeficiency, centromeric heterochromatin instability and facial syndrome. The chromosomal karyotyping report was showing instability around vicinity of chromosome 1 and various abnormalities around vicinity of both chromosomes 1 were found in form of random breakages of chromosome 1, fragile sites, deletions/duplications of small and long arm, extra copies of chromosome 1 with rosette formations, exchange of arms and partial aneuploidies of chromosome 1. Further, the investigations regarding the immune status revealed that the level of IgM (5.98 mg/dl), IgA (<6.16mg/dl) and IgG (92.10 mg/dl) subgroup of immunoglobulin was very low. The results were consistent with The Immunodeficiency, Centromeric region instability, Facial anomalies (ICF) syndrome. Second sample from the patient for molecular studies could not be collected and performed since the patient failed to survive after 3 and half months.
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Boroń, Alicja, Anna Grabowska, Aneta Spóz i Anna Przybył. "B Chromosomes and Cytogenetic Characteristics of the Common Nase Chondrostoma nasus (Linnaeus, 1758)". Genes 11, nr 11 (6.11.2020): 1317. http://dx.doi.org/10.3390/genes11111317.
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Supernumerary B chromosomes (Bs) are very promising structures, among others, in that they are an additional genomic compartment for evolution. In this study, we tested the presence and frequency of B chromosomes and performed the first cytogenetic examination of the common nase (Chondrostoma nasus). We investigated the individuals from two populations in the Vistula River basin, in Poland, according to the chromosomal distribution of the C-bands and silver nucleolar organizer regions (Ag-NORs), using sequential staining with AgNO3 and chromomycin A3 (CMA3). Furthermore, we analyzed the chromosomal localization of two rDNA families (45S and 5S rDNA) using fluorescence in situ hybridization (FISH) with rDNA probes. Chondrostoma nasus individuals showed a standard (A) chromosome set consisting of 2n = 50: 12 metacentric, 32 submetacentric, and 6 acrocentric chromosomes (NF = 94). Fourteen out of the 20 analyzed individuals showed 1–2 mitotically unstable submetacentric B chromosomes of different sizes. Six of them, in 14.1% of the analyzed metaphase plates, had a single, medium-sized submetacentric B (Bsm) chromosome (2n = 51) with a heterochromatic block located in its pericentromeric region. The other seven individuals possessed a Bsm (2n = 51) in 19.4% of the analyzed metaphase plates, and a second Bsm chromosome (2n = 52), the smallest in the set, in 15.5% of metaphase plates, whereas one female was characterized by both Bsm chromosomes (2n = 52) in 14.3% of the analyzed metaphase plates. AgNORs, GC-rich DNA sites, and 28S rDNA hybridization sites were observed in the short arms of two submetacentric chromosome pairs of A set. The constitutive heterochromatin was visible as C bands in the centromeric regions of almost all Chondrostoma nasus chromosomes and in the pericentromeric region of several chromosome pairs. Two 5S rDNA hybridization sites in the pericentromeric position of the largest acrocentric chromosome pair were observed, whereas two other such sites in co-localization on a smaller pair of NOR chromosomes indicate a species-specific character. The results herein broaden our knowledge in the field of B chromosome distribution and molecular cytogenetics of Chondrostoma nasus: a freshwater species from the Leuciscidae family.
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Ta, Lan, Adrian Zordan, Bruce Mercer, Lynda J. Campbell i Ruth N. MacKinnon. "The Breakage-Fusion-Bridge Cycle Producing MLL Amplification in a Case of Myelodysplastic Syndrome". Journal of Cancer Research 2013 (18.07.2013): 1–6. http://dx.doi.org/10.1155/2013/452809.
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Telomere loss may lead to chromosomal instability via the breakage-fusion-bridge (BFB) cycle which can result in genetic amplification and the formation of ring and dicentric chromosomes. This cycle continues until stable chromosomes are formed. The case of a 72-year-old female with refractory anaemia with excess blasts type 2 illustrates these events. Conventional cytogenetics produced a complex karyotype which included unstable abnormalities of chromosomes 11, 12, and 15. Fluorescence in situ hybridization (FISH) analyses including multicolor-FISH (M-FISH) and multicolor-banding (M-BAND) revealed multiple clonal populations with 5 copies of MLL on either a ring chromosome composed entirely of chromosome 11 material or a derivative chromosome composed of chromosomes 11, 12, and 15. The FISH results also clarified the likely evolution of the karyotypic complexity. The simplest cell line contained a dic(12;15) in addition to copy number aberrations that are typical of MDS or AML. As the disease progressed, a ring 11 was formed. Subsequently, the ring 11 appears to have unwound and inserted itself into the dic(12;15) chromosome followed by an inversion of the derivative chromosome, producing a der(11;15;12). Telomeric loss and BFB cycles appear to have played an important role in the chromosomal rearrangements and clonal evolution demonstrated in the karyotype.