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1
Echt, C. S., K. K. Kidwell, S. J. Knapp, T. C. Osborn, and T. J. McCoy. "Linkage mapping in diploid alfalfa (Medicago sativa)." Genome 37, no. 1 (February 1, 1994): 61–71. http://dx.doi.org/10.1139/g94-008.
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A genome map of cultivated alfalfa was constructed using segregating restriction fragment length polymorphisms (RFLPs) and random amplified polymorphic DNAs (RAPDs) in a diploid backcross population generated from noninbred parents. Among the 153 loci scored in 87 progeny, four segregation ratios were observed for codominant and dominant markers: 1:1, 1:2:1, 1:1:1:1, and 3:1. Deviations from expected Mendelian ratios (p < 0.05) were observed for 34% of the loci studied. A genome map was assembled from two separate linkage maps, each constructed from a subset of the segregation data. One linkage map was constructed from 46 RFLP and 40 RAPD markers segregating 1:1 from the F1 parent of the backcross and the other linkage map was constructed from 33 RFLP and 28 RAPD markers segregating 1:1 from the recurrent parent. Sixteen loci with alleles segregating 1:1 from both parents were used as locus bridges to align individual linkage groups between the two maps. The combined use of RFLPs and RAPDs was an effective method for developing an alfalfa genome map.Key words: genome mapping, RAPD, RFLP, locus bridges.
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Rubino, David B. "Inheritance of Esterase, Diaphorase, and Glucose-6-phosphate Isomerase in Lisianthus." HortScience 28, no. 6 (June 1993): 661–63. http://dx.doi.org/10.21273/hortsci.28.6.661.
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Segregating lisianthus [Eustoma grandiflorum (Griseb.) Shinn.] progeny were evaluated to determine the inheritance of esterase (EST), diaphorase (DIA), and glucose-6-phosphate isomerase (GPI) isozymes. Phenotypic data supported the hypotheses that EST is monomeric and controlled by one locus (Est1) with at least three alleles, DIA is tetrameric and controlled by one locus (Dia2) with at least two alleles, and GPI is controlled by one locus (Gpil) with at least two alleles. The structure of the GPI isozyme could not be inferred from banding patterns. Joint segregation analyses indicated that the three loci segregate independently. These three isozymes are the first simply inherited, unlinked biochemical markers identified in lisianthus. These marker loci will be useful for genetic studies, breeding, and germplasm characterization.
3
Havey, Michael J. "Genetic Mapping of Chartreuse Bulb Color in Onion." Journal of the American Society for Horticultural Science 145, no. 2 (March 2020): 110–19. http://dx.doi.org/10.21273/jashs04861-20.
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The most common bulb colors of onion (Allium cepa) are red, yellow, and white; chartreuse is a relatively rare bulb color conditioned by the homozygous recessive genotype at the G locus. In this research, plants with chartreuse bulbs were crossed with inbreds with yellow bulbs to develop segregating families for genetic mapping of the G locus. For all of 17 F2 families, segregations for yellow vs. chartreuse bulbs fit the expected 3:1 ratio (P > 0.05). DNAs were isolated from one F2 family and genotyped for single nucleotide polymorphisms (SNPs) to produce a genetic map of the G locus and 380 SNPs, of which 119 SNPs have not been previously mapped. Segregations for yellow vs. chartreuse bulbs placed the G locus at the end of chromosome 7 at 6.7 cM from the nearest SNP (isotig28625_2789). This codominant SNP marker linked to the G locus should be useful for introgression of recessive chartreuse bulb color into diverse onion populations for commercial production of this uniquely colored onion.
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Monnahan, Patrick J., and John K. Kelly. "Naturally segregating loci exhibit epistasis for fitness." Biology Letters 11, no. 8 (August 2015): 20150498. http://dx.doi.org/10.1098/rsbl.2015.0498.
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The extent to which gene interaction or epistasis contributes to fitness variation within populations remains poorly understood, despite its importance to a myriad of evolutionary questions. Here, we report a multi-year field study estimating fitness of Mimulus guttatus genetic lines in which pairs of naturally segregating loci exist in an otherwise uniform background. An allele at QTL x5b—a locus originally mapped for its effect on flower size—positively affects survival if combined with one genotype at quantitative trait locus x10a (aa) but has negative effects when combined with the other genotypes (Aa and AA). The viability differences between genotypes parallel phenotypic differences for the time and node at which a plant flowers. Viability is negatively correlated with fecundity across genotypes, indicating antagonistic pleiotropy for fitness components. This trade-off reduces the genetic variance for total fitness relative to the individual fitness components and thus may serve to maintain variation. Additionally, we find that the effects of each locus and their interaction often vary with the environment.
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Groover, A., M. Devey, T. Fiddler, J. Lee, R. Megraw, T. Mitchel-Olds, B. Sherman, S. Vujcic, C. Williams, and D. Neale. "Identification of quantitative trait loci influencing wood specific gravity in an outbred pedigree of loblolly pine." Genetics 138, no. 4 (December 1, 1994): 1293–300. http://dx.doi.org/10.1093/genetics/138.4.1293.
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Abstract We report the identification of quantitative trait loci (QTL) influencing wood specific gravity (WSG) in an outbred pedigree of loblolly pine (Pinus taeda L.). QTL mapping in an outcrossing species is complicated by the presence of multiple alleles (> 2) at QTL and marker loci. Multiple alleles at QTL allow the examination of interaction among alleles at QTL (deviation from additive gene action). Restriction fragment length polymorphism (RFLP) marker genotypes and wood specific gravity phenotypes were determined for 177 progeny. Two RFLP linkage maps were constructed, representing maternal and paternal parent gamete segregations as inferred from diploid progeny RFLP genotypes. RFLP loci segregating for multiple alleles were vital for aligning the two maps. Each RFLP locus was assayed for cosegregation with WSG QTL using analysis of variance (ANOVA). Five regions of the genome contained one or more RFLP loci showing differences in mean WSG at or below the P = 0.05 level for progeny as grouped by RFLP genotype. One region contained a marker locus (S6a) whose QTL-associated effects were highly significant (P > 0.0002). Marker S6a segregated for multiple alleles, a prerequisite for determining the number of alleles segregating at the linked QTL and analyzing the interactions among QTL alleles. The QTL associated with marker S6a appeared to be segregating for multiple alleles which interacted with each other and with environments. No evidence for digenic epistasis was found among the five QTL.
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Lawson, Darlene M., Minou Hemmat, and Norman F. Weeden. "The Use of Molecular Markers to Analyze the Inheritance of Morphological and Developmental Traits in Apple." Journal of the American Society for Horticultural Science 120, no. 3 (May 1995): 532–37. http://dx.doi.org/10.21273/jashs.120.3.532.
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Five morphological and developmental traits (branching habit, vegetative budbreak, reproductive budbreak, bloom time, and root suckering) were analyzed in a family obtained from the apple (Malus domestica Borkh) cross `Rome Beauty' × `White Angel'. The phenotypic variation in these traits was compared with a selected set of marker loci covering the known genome of each of the parents to locate genes with major effects on the traits. The contrasting branching habits of the two parents appeared to be controlled by at least two loci. One of these, Tb, governed the presence or absence of lateral branches, particularly on the lower half of shoots. The locus was heterozygous in `White Angel' and was mapped to a 5 CM interval on linkage group 6. At least one other locus conditioning spur-type branching appeared to be segregating, but the locus or loci could not be linked to segregating markers. The timing of initial vegetative growth was tightly associated with the chromosomal region in which the Tb gene is located and maybe a pleiotropic effect of this gene. Time of reproductive budbreak correlated with segregation at the isozyme marker, Prx-c, on linkage group 5. Variation in time of bloom and later stages in flower development appeared to be controlled by different genes not linked to Prx-c. The tendency to produce root suckers cosegregated with a marker on `White Angel' linkage group 1, suggesting control by a single locus, Rs. Data from a `Rome Beauty' x `Robusta 5' family provided additional information on the inheritance of these traits.
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Mehlenbacher, Shawn A., and Maxine M. Thompson. "Inheritance of Style Color in Hazelnut." HortScience 39, no. 3 (June 2004): 475–76. http://dx.doi.org/10.21273/hortsci.39.3.475.
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The style color of standard hazelnut (Corylus avellana L.) cultivars ranges from pink to dark purple. Styles with an unusual yellow color were first noted in seedlings of the progeny `Goodpasture' × `Compton', and the ratio was ≈3 red: 1 yellow. Controlled crosses were made to investigate the genetic control of style color. The same 3:1 ratio was observed in four additional crosses in which both parents had red styles. Two crosses of a red and a yellow parent gave ≈50% yellow styles, while a cross of two selections with yellow styles gave only seedlings with yellow styles. These segregation ratios indicate control by a single locus, with yellow style color recessive to red. Seedlings with yellow styles have green buds and catkins and a more upright growth habit than their siblings with red styles. Inspection of the pedigrees of these progenies shows that `Daviana', `Willamette', `Butler', `Compton', `Goodpasture', and `Lansing #1' are heterozygous. `Daviana' appears to be the original source of the allele for yellow styles, as it is a known or suspected parent or ancestor of the others. Ratios in a progeny segregating simultaneously for growth habit (normal vs. contorted) and style color indicated independence of the traits. However, in a progeny segregating simultaneously for leaf color (red vs. green) and style color, no redleaf seedlings had yellow styles. The S-alleles of eight genotypes with yellow styles were determined, and indicate a possible linkage between the yellow style locus and the S locus that controls pollen-stigma incompatibility. One explanation is that the yellow style trait is conferred by an allele (ays) at the anthocyanin (A) locus that controls leaf color. A second explanation is that there is a yellow style locus closely linked to the A locus. The A locus is known to be loosely linked to the S locus.
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Labonne, J. D. J., A. Vaisman, and J. S. Shore. "Construction of a first genetic map of distylous Turnera and a fine-scale map of the S-locus region." Genome 51, no. 7 (July 2008): 471–78. http://dx.doi.org/10.1139/g08-031.
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As a prelude to discovery of genes involved in floral dimorphism and incompatibility, a genetic map of distylous Turnera was constructed along with a fine-scale map of the S-locus region. The genetic map consists of 79 PCR-based molecular markers (48 AFLP, 18 RAPD, 9 ISSR, 4 RAMP), 5 isozyme loci, one additional gene, and the S-locus, spanning a total distance of 683.3 cM. The 86 markers are distributed in 5 linkage groups, corresponding to the haploid chromosome number. Molecular markers tightly linked or co-segregating with the S-locus in an initial mapping population of 94 individuals were used to assay an additional 642 progeny to construct a map of the S-locus region. The fine-scale map consists of 2 markers (IS864a and RP45E9) flanking the S-locus at distances of 0.41 and 0.54 cM, respectively, and 3 additional markers (OPK14c, RP45G18, and RP81E18) co-segregating with the S-locus in the total mapping population of 736 individuals. The genetic map constructed will serve as a framework for localization of genes outside the S-locus affecting distyly, while molecular markers of the fine-scale map will be used to initiate chromosome walking to find the genes residing at the S-locus.
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Perry, D. J., and P. Knowles. "Inheritance and linkage relationships of allozymes of eastern white cedar (Thuja occidentalis) in northwestern Ontario." Genome 32, no. 2 (April 1, 1989): 245–50. http://dx.doi.org/10.1139/g89-435.
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Allozyme variants of 12 enzyme systems were examined in seed tissues of eastern white cedar (Thuja occidentalis L.), using starch gel electrophoresis. Nine loci were polymorphic and deviation from a 1:1 segregation ratio was observed between two of three alleles at one locus (Mdh-1). Of the possible 36 locus-pair combinations, 23 could be tested for linkage. Significant linkage was detected for three pairs of loci (Aat-1/Mdh-1, Aat-1/Pgm, and Idh-2/Me). Trees jointly segregating for Aat-1 and Pgm fell into two classes, one with a low recombination frequency (9.1%) and the other with a higher recombination frequency (26.6%). An inversion polymorphism is a possible cause of this linkage heterogeneity observed among trees.Key words: allozymes, isozymes, inheritance, linkage, eastern white cedar, northern white cedar, Thuja occidentalis L., Cupressaceae.
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Gao, Feng, Arvind H. Hirani, Jun Liu, Zheng Liu, Guohua Fu, Chunren Wu, Peter B. E. McVetty, and Genyi Li. "Fine Mapping a Clubroot Resistance Locus in Chinese Cabbage." Journal of the American Society for Horticultural Science 139, no. 3 (May 2014): 247–52. http://dx.doi.org/10.21273/jashs.139.3.247.
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There are various clubroot pathogen (Plasmodiophora brassicae) resistance genes within Brassica species with european turnip (B. rapa ssp. rapifera) being identified as potentially the best source of resistance for the development of clubroot-resistant cultivars in chinese cabbage (B. rapa ssp. pekinensis). To use clubroot resistance genes effectively, it is necessary to map these genes so that molecular markers inside or closely linked to these resistance genes can be developed. Using molecular marker-assisted selection, the clubroot resistance genes can be effectively transferred from cultivar to cultivar and from species to species. In this report, one clubroot resistance locus was mapped on linkage group A3 using five segregating populations developed from five chinese cabbage cultivars, suggesting that all the five cultivars shared the same clubroot resistance locus. Furthermore, one of these five chinese cabbage cultivars was used to develop a large segregating population to fine-map this clubroot resistance locus to a 187-kilobp chromosomal region. Molecular markers that are closely linked to the mapped clubroot resistance locus have been developed that can be used for marker-assisted selection in chinese cabbage and canola/rapeseed (B. rapa and B. napus) breeding programs.
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Anhalt, Ulrike C. M., Katharina Martini, Ernst-Heinrich Ruehl, and Astrid Forneck. "Tracing Heterozygosity in the Vvlexp1 Locus in Grapevine by Sequencing and High-resolution Melt Analysis." Journal of the American Society for Horticultural Science 138, no. 2 (March 2013): 120–24. http://dx.doi.org/10.21273/jashs.138.2.120.
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Multiple loci in a continuously asexually reproducing genome such as vegetatively propagated grapevine (Vitis vinifera) can be heterozygote. The methodology to analyze heterozygous loci is manifold ranging from traditional breeding and studying segregating offspring, codominant marker analyses to whole sequence analysis. Results of heterozygosity studies on challenging loci need to be carefully confirmed to ensure accuracy and avoid misinterpretation. One of these methods is high-resolution melt (HRM) analysis in combination with sequencing and segregation analysis. We present first the adoption of HRM analyses for grapevine and its potential to confirm heterozygotic markers with low or no sequence size differences.
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Ron, Micha, David Kliger, Esther Feldmesser, Eyal Seroussi, Ephraim Ezra, and Joel Ira Weller. "Multiple Quantitative Trait Locus Analysis of Bovine Chromosome 6 in the Israeli Holstein Population by a Daughter Design." Genetics 159, no. 2 (October 1, 2001): 727–35. http://dx.doi.org/10.1093/genetics/159.2.727.
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Abstract Nine Israeli Holstein sire families with 2978 daughters were analyzed for quantitative trait loci effects on chromosome 6 for five milk production traits by a daughter design. All animals were genotyped for 2 markers. The three families with significant effects were genotyped for up to 10 additional markers spanning positions 0–122 cM of BTA6. Two sires were segregating for a locus affecting protein and fat percentage near position 55 cM with an estimated substitution effect of 0.18% protein, which is equivalent to one phenotypic standard deviation. This locus was localized to a confidence interval of 4 cM. One of these sires was also heterozygous for a locus affecting milk, fat, and protein production near the centromere. The hypothesis of two segregating loci was verified by multiple regression analysis. A third sire was heterozygous for a locus affecting milk and protein percentage near the telomeric end of the chromosome. Possible candidates for the major quantitative gene near position 55 cM were determined by comparative mapping. IBSP and SSP1 were used as anchors for the orthologous region on human chromosome 4. Twelve genes were detected within a 2-Mbp sequence. None of these genes have been previously associated with lactogenesis.
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Lester, Diane R., Wayne B. Sherman, and Brian J. Atwell. "Endopolygalacturonase and the Melting Flesh (M) Locus in Peach." Journal of the American Society for Horticultural Science 121, no. 2 (March 1996): 231–35. http://dx.doi.org/10.21273/jashs.121.2.231.
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Southern analysis of two ripening-related polygalacturonase (PG) genes of peach [Prunus persica (L.) Batsch] detected a restriction fragment length polymorphism (RFLP) in one that had been previously identified as encoding the endoPG enzyme of melting flesh fruit. This RFLP distinguished the melting flesh cultivars Flavorcrest and Flordaking from the nonmelting flesh cultivars Carolyn, Early Gold Queen, Fla. 86-28C, and Fla. 9-26C. Complete deletion of endoPG-related genomic sequences was demonstrated in the nonmelting flesh variety Fla. 9-20C. In a blind trial, segregation of the endoPG RFLP was followed in relation to the melting flesh trait in a population of 20 trees from `Fla. 86-28C' × `Springcrest' in which the trait was segregating 1:1. Cosegregation of the RFLP with the trait occurred for 17 out of 20 trees. Practical aspects of scoring the melting flesh trait in a genetically variable population may account for incomplete segregation. EndoPG protein was detected by western blotting in fruit of the melting flesh cultivars Flavorcrest and Fragar, but not in fruit of the nonmelting flesh cultivar Carolyn. Results from this study and earlier work are used to discuss the hypothesis that the endoPG gene corresponds to the melting flesh (M) locus of peach.
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Birchler, J. A., and J. C. Hiebert. "Interaction of the Enhancer of white-apricot with transposable element alleles at the white locus in Drosophila melanogaster." Genetics 122, no. 1 (May 1, 1989): 129–38. http://dx.doi.org/10.1093/genetics/122.1.129.
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Abstract The Enhancer of wa [E(wa)] mutation was shown to interact strongly with 4 of 41 tested alleles of the white (w) eye color locus. All four of the affected w alleles result from the insertion of a transposable element. E(wa) was further localized cytogenetically. The locus lies between the breakpoints of T(Y;2)L11 and T(Y;2)H137 (section 60) in 2R. The original mutation was shown to be antimorphic on the basis of its action in the presence of additional normal copies and the ability to revert the original allele to one that mimics the effect of a deficiency for the locus. The RNA transcribed from wa was analyzed from flies segregating for E(wa) and normal. The low level of normal functional messenger RNA present in white-apricot is reduced further in Enhancer homozygotes. Total copia RNA was also examined on Northern analyses from the segregating population but no quantitative change in the major copia RNA was produced by E(wa) homozygotes compared to normal.
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Zewdie, Yayeh, Michael J. Havey, James P. Prince, and Maria M. Jenderek*. "Genetic Linkage Map of Garlic (Allium sativum)." HortScience 39, no. 4 (July 2004): 775A—775. http://dx.doi.org/10.21273/hortsci.39.4.775a.
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Garlic has been propagated exclusively by asexual means since time immemorial. The recent discovery of male fertile garlic accessions allowed studies on genetics and garlic improvement. Single nucleotide polymorphism (SNP) and random amplified polymorphic DNA (RAPD) based genetic linkage map was developed for garlic using a segregating population derived from one plant of PI 540316. Progenies segregated for male fertility and other morphological characters. Distortion of segregation was observed for most of the markers. This was expected due to the segregation of recessive deleterious alleles present in the garlic genome. The map contained 23 loci distributed on five linkage groups. It covered 319 cM with the average of 18 cM between loci. Linkage with the male fertility (Mf) locus was established with SNP marker AOB155 (26.7 cM).
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Schäfer-Pregl, R., F. Salamini, and C. Gebhardt. "Models for mapping quantitative trait loci (QTL) in progeny of non-inbred parents and their behaviour in presence of distorted segregation ratios." Genetical Research 67, no. 1 (February 1996): 43–54. http://dx.doi.org/10.1017/s0016672300033462.
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SummaryIn plants, models for mapping quantitative trait loci (QTL) based on flanking markers have been mainly developed for progenies of inbred lines. We propose twoflanking marker models for QTL mapping in F1 progenies of non-inbred parents. The first is based on the segregation of four different scorable alleles at a marker locus (the four-allele model) and the second (the commonallele model) on one scorable allele per marker locus segregating in both parents. These models are suitable for the majority of the allelic configurations which may occur in crosses between heterozygous parents. For both cases, when four scorable or one common-allele per marker locus segregate, additional algorithms were developed to estimate the recombination frequency between two marker loci. Tests carried out with simulated populations of various sizes indicate that the models provide a good estimate of QTL genotypic means and of recombination frequencies between flanking markers and between the marker loci and the QTL.The estimates of QTL genotypic means have a higher precision than the estimates of recombination frequencies. The four-allele model shows a higher ability to detect QTLs than the common-allele model. If segregation ratios are distorted, the power of both models and the precision of the estimates of recombination frequencies are reduced, whereas the accuracy of estimates of QTL genotype means is not affected by distorted segregation ratios. The power of the common-allele model is substantially reduced if QTL genotypic means depend on additive allelic interactions, whereas the four-allele model is less affected by the non-additive behaviour of QTL alleles.
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Foolad, M. R. "Unilateral Incompatibility as a Major Cause of Skewed Segregation in the Cross between Lycopersicon esculentum and L. pennellii." HortScience 31, no. 4 (August 1996): 625d—625. http://dx.doi.org/10.21273/hortsci.31.4.625d.
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Skewed segregations are frequent events in segregating populations derived from different interspecific crosses in tomato. To determine a basis for skewed segregations in the progeny of the cross between Lycopersicon esculentum and L. pennellii, monogenic segregations of 16 isozyme loci were analyzed in an F2 and two backcross populations of this cross. In the F2, nine loci mapping to chromosomes 1, 2, 4, 9, 10, and 12 exhibited skewed segregations and in all cases there was an excess of L. pennellii homozygotes. The genotypic frequencies at all but one locus were at Hardy–Weinberg equilibria. In the backcross populations, all except two loci exhibited normal Mendelian segregations. No postzygotic selection model could statistically or biologically explain the observed segregation patterns. A prezygotic selection model, assuming selective elimination of the male gametophytes during pollen function (i.e., from pollination to karyogamy) adequately explained the observed segregations in all three populations. The direction of the skewed segregations in the F2 was consistent with that expected based on the effects of unilateral incompatibility reactions between the two species. In addition, the chromosomal locations of five of the nine markers that exhibited skewed segregations coincided with the locations of several known compatibility-related genes in tomato. Multigenic unilateral incompatibility reactions between L. esculentum pollen and the stigma or style of L. pennellii (or its hybrid derivatives) are suggested to be the major cause of the skewed segregations in the F2 progeny of this cross.
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Cousineau, Johanne C., and Danielle J. Donnelly. "Genetic Analysis of Isoenzymes in Raspberry." Journal of the American Society for Horticultural Science 117, no. 6 (November 1992): 996–99. http://dx.doi.org/10.21273/jashs.117.6.996.
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The inheritance of five isoenzymes was studied in red and purple raspberry F1 progenies (Rubus idaeus L. and Rubus × neglectus Peck). Isocitrate dehydrogenase (IDH; EC 1.1.1.42) was a dimeric enzyme present in the cytosol and coded for by one locus (Idh-1). Three of the four crosses analyzed at this locus had deviations from expected ratios, possibly caused by its linkage to a recessive lethal gene. Malate dehydrogenase (MDH; EC 1.1.1.37), phosphoglucoisomerase (PGI; EC 5.3.1.9), and triose phosphate isomerase (TPI; EC 5.3.1.1) were dimeric enzymes with two loci. Each of these three enzymes was present in an organelle and in the cytosol for locus 1 and 2, respectively. Phosphoglucomutase (PGM; EC 2.7.5.1) was monomeric with two loci, Pgm-1 and Pgm-2, located in an organelle and the cytosol, respectively. Each allele at Pgm-1 resulted in the formation of two bands. Although most progenies analyzed supported Mendelian inheritance of polymorphic loci (except for Idh-1), there was a higher than expected number of aberrant segregation ratios observed (18.4%). Analysis of 85 pairs of jointly segregating loci revealed a possible linkage group consisting of Mdh-2, Tpi-2, and Pgm-1.
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van den Berg, J. H., M. W. Bonierbale, E. E. Ewing, R. L. Plaisted, and S. D. Tanksley. "CHARACTERIZATION OF SEGREGATING POTATO PROGENIES FOR TUBERIZATION RESPONSE TO PHOTOPERIOD IN CONNECTION WITH GENETIC MAPPING." HortScience 27, no. 11 (November 1992): 1161c—1161. http://dx.doi.org/10.21273/hortsci.27.11.1161c.
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Tuberization and stolonization of cuttings were used as a model system to assess response to photoperiod in segregating potato progenies. The progenies were from backcrosses of a diploid hybrid between Solanum tuberosum and the short day requiring S. berthaultii to both parent species. Restriction Fragment Length Polymorphism (RFLP) analyses had been performed on these progenies as a part of other investigations. The RFLP maps were used to identify the loci controlling the photoperiod responses characterized by the cuttings. In the S. berthaultii backcross population, one locus appeared to control the response of cuttings only under long photoperiods, and coincided with a locus detected for stolonization on whole plants; a second locus was effective for tuberization under short photoperiods but was not detected with certainty under long photoperiods. Data analysis for the second backcross population is currently underway.
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Chen, Andrew, Jiaman Sun, Altus Viljoen, Diane Mostert, Yucong Xie, Leroy Mangila, Sheryl Bothma, et al. "Genetic Mapping, Candidate Gene Identification and Marker Validation for Host Plant Resistance to the Race 4 of Fusarium oxysporum f. sp. cubense Using Musa acuminata ssp. malaccensis." Pathogens 12, no. 6 (June 9, 2023): 820. http://dx.doi.org/10.3390/pathogens12060820.
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Fusarium wilt of banana is a devastating disease that has decimated banana production worldwide. Host resistance to Fusarium oxysporum f. sp. Cubense (Foc), the causal agent of this disease, is genetically dissected in this study using two Musa acuminata ssp. Malaccensis segregating populations, segregating for Foc Tropical (TR4) and Subtropical (STR4) race 4 resistance. Marker loci and trait association using 11 SNP-based PCR markers allowed the candidate region to be delimited to a 12.9 cM genetic interval corresponding to a 959 kb region on chromosome 3 of ‘DH-Pahang’ reference assembly v4. Within this region, there was a cluster of pattern recognition receptors, namely leucine-rich repeat ectodomain containing receptor-like protein kinases, cysteine-rich cell-wall-associated protein kinases, and leaf rust 10 disease-resistance locus receptor-like proteins, positioned in an interspersed arrangement. Their transcript levels were rapidly upregulated in the resistant progenies but not in the susceptible F2 progenies at the onset of infection. This suggests that one or several of these genes may control resistance at this locus. To confirm the segregation of single-gene resistance, we generated an inter-cross between the resistant parent ‘Ma850’ and a susceptible line ‘Ma848’, to show that the STR4 resistance co-segregated with marker ‘28820’ at this locus. Finally, an informative SNP marker 29730 allowed the locus-specific resistance to be assessed in a collection of diploid and polyploid banana plants. Of the 60 lines screened, 22 lines were predicted to carry resistance at this locus, including lines known to be TR4-resistant, such as ‘Pahang’, ‘SH-3362’, ‘SH-3217’, ‘Ma-ITC0250’, and ‘DH-Pahang/CIRAD 930’. Additional screening in the International Institute for Tropical Agriculture’s collection suggests that the dominant allele is common among the elite ‘Matooke’ NARITA hybrids, as well as in other triploid or tetraploid hybrids derived from East African highland bananas. Fine mapping and candidate gene identification will allow characterization of molecular mechanisms underlying the TR4 resistance. The markers developed in this study can now aid the marker-assisted selection of TR4 resistance in breeding programs around the world.
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Clark, Rebecca, Sarah M. Brown, Steve C. Collins, Chris D. Jiggins, David G. Heckel, and Alfried P. Vogler. "Colour pattern specification in the Mocker swallowtail Papilio dardanus : the transcription factor invected is a candidate for the mimicry locus H." Proceedings of the Royal Society B: Biological Sciences 275, no. 1639 (February 19, 2008): 1181–88. http://dx.doi.org/10.1098/rspb.2007.1762.
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The swallowtail butterfly, Papilio dardanus , is an iconic example of a polymorphic Batesian mimic. The expression of various female-limited colour forms is thought to be controlled by a single autosomal locus, termed H , whose function in determining the wing pattern remains elusive. As a step towards the physical mapping of H , we established a set of 272 polymorphic amplified fragment length polymorphism (AFLP) markers ( Eco RI- Mse I). Segregation patterns in a ‘female-informative’ brood (exploiting the absence of crossing over in female Lepidoptera) mapped these AFLPs to 30 linkage groups (putative chromosomes). The difference between the hippocoon and cenea female forms segregating in this family resides on a single one of these linkage groups, defined by 14 AFLPs. In a ‘male-informative’ cross (markers segregating within a linkage group), a pair of AFLPs co-segregated closely with the two female forms, except in four recombinants out of 19 female offspring. Linkage with these AFLP markers using four further female-informative families demonstrated that the genetic factor determining other morphs ( poultoni , lamborni and trimeni ) also maps to this same linkage group. The candidate gene invected , obtained in a screen for co-segregation of developmental genes with the colour forms, resides in a 13.9 cM interval flanked by the two AFLP markers. In the male-informative family invected co-segregated perfectly with the hippocoon / cenea factor, despite the four crossovers with the AFLPs. These findings make invected , and possibly its closely linked paralogue engrailed , strong candidates for H . This is supported by their known role in eyespot specification in nymphalid butterfly wings.
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Wang, Xindan, and David J. Sherratt. "Independent Segregation of the Two Arms of the Escherichia coli ori Region Requires neither RNA Synthesis nor MreB Dynamics." Journal of Bacteriology 192, no. 23 (October 1, 2010): 6143–53. http://dx.doi.org/10.1128/jb.00861-10.
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ABSTRACT The mechanism of Escherichia coli chromosome segregation remains elusive. We present results on the simultaneous tracking of segregation of multiple loci in the ori region of the chromosome in cells growing under conditions in which a single round of replication is initiated and completed in the same generation. Loci segregated as expected for progressive replication-segregation from oriC, with markers placed symmetrically on either side of oriC segregating to opposite cell halves at the same time, showing that sister locus cohesion in the origin region is local rather than extensive. We were unable to observe any influence on segregation of the proposed centromeric site, migS, or indeed any other potential cis-acting element on either replication arm (replichore) in the AB1157 genetic background. Site-specific inhibition of replication close to oriC on one replichore did not prevent segregation of loci on the other replichore. Inhibition of RNA synthesis and inhibition of the dynamic polymerization of the actin homolog MreB did not affect ori and bulk chromosome segregation.
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Hawkins, Leigh K., Fenny Dane, Tom Kubisiak, Bill Rhodes, and Bob Jarrett. "Genome Mapping in Citrullus Lanatus Populations Segregating for Fusarium Wilt Resistance." HortScience 35, no. 4 (July 2000): 558C—558b. http://dx.doi.org/10.21273/hortsci.35.4.558c.
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A linkage map was constructed of the watermelon genome using F2 and F2:3 populations segregating for resistance to race 1 and 2 of Fusarium oxysporum f. sp. niveum (FON 1 and 2). Sixty-four percent of the RAPD primers used in the parents and F1 detected polymorphism. In the F2, 143 polymorphic bands were scored, 60% of which exhibited the expected 3:1 segregation ratio. A 113 cM linkage map was constructed using Mapmaker version 3 and LOD of 4. DNA pools of Fusarium wilt resistant or susceptible F2:3 lines were created and bulked segregant analysis was used to detect molecular markers linked to FON 1 or FON 2 resistance. Four individuals per line were used to confirm linkages and construct an F2:3 linkage map. One large linkage group was detected in both generations. A large proportion of the RAPD and SSR markers were unlinked and many showed segregation distortion. Single-factor ANOVA for each pairwise combination of marker locus and resistance or morphological trait was conducted. RAPD markers with putative linkages to FON 1 and FON 2 and several morphological traits were detected.
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Zeng, Linghe, and Wm Vance Baird. "Inheritance of High Levels of Resistance to Microtubule-disrupting Herbicides in a Weedy Grass, and Molecular-tagging of the Genetic Locus." HortScience 32, no. 3 (June 1997): 534C—534. http://dx.doi.org/10.21273/hortsci.32.3.534c.
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Dinitroaniline herbicides exert their phytotoxic effect by interfering with tubulin dimer polymerization; thus, these and other anti-mitotic drugs destabilize cytoplasmic and spindle microtubules. The dinitroanilines are particularly effective on monocotyledonous species. A naturally occurring mutant of goosegrass [Eleusine indica (L.) Gaertn.], resistant (R) to the DNHs, and the widely distributed susceptible, wild-type (S) have been collected from a number of agricultural sites throughout the southeastern U.S. Pairs of these accessions were cross-pollinated to create F1 individuals, from which F2 and F3 generations were developed through natural self-pollination. Analysis of the dinitroaniline herbicide response phenotype (DRP) has shown the F1s to be susceptible, and the F2 and F3 to be segregating 3:1 for susceptibility and resistance, respectively (i.e., 3S:1R). This genetic data is consistent with the DRP being encoded by a single, nuclear locus. Random amplified polymorphic DNA (RAPD) analysis of a segregating F2 population (N = 60), which identified 32 linked and 33 unlinked molecular markers, supports this hypothesis of simple Mendelian inheritance. Furthermore, this RAPD analysis coupled with restriction fragment length polymorphism (RFLP) analysis, localized the DRP locus to a single chromosomal region and identified two RAPD-markers, and at least one RFLP-marker, flanking the DRP locus. This information provides a starting point for map-based (i.e., positional) cloning of the resistance (DRPr) and susceptibility (DRPs) alleles.
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Eastwood, R. F., E. S. Lagudah, and R. Appels. "A directed search for DNA sequences tightly linked to cereal cyst nematode resistance genes in Triticum tauschii." Genome 37, no. 2 (April 1, 1994): 311–19. http://dx.doi.org/10.1139/g94-043.
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An improved system for identifying DNA sequences linked to a targeted region was developed by fractionating DNA sequences prior to polymerase chain reaction (PCR) analysis. In an attempt to identify DNA markers linked to a strong CCN resistance gene, Ccn-D1, in Triticum tauschii, DNA samples from individuals homozygous for resistance and susceptibility at the Ccn-D1 locus in a segregating progeny were bulked separately to produce "near isogenic" DNA pools. The polymerase chain reaction was employed to generate several DNA amplification products from each of the bulked DNA segregants using 240 random (RAPD) and 4 semirandom (consensus sequences of intron–splice junctions) primers. A DNA polymorphic fragment was apparent between the resistant and susceptible bulks using one of the semirandom primers. Hydroxylapatite chromatography of reannealed DNA (to Cot values > 100) was used to enrich low copy DNA sequences in the bulk DNA segregants (resistant and susceptible DNA pools). PCR analysis on the low copy enriched DNA pool increased the level of polymorphism detected between bulked segregants. One of the RAPD fragments present in only the resistant low copy DNA pool was cloned and mapped to the distal region of the long arm of chromosome 2D. By using the cloned RAPD fragment, csE20-2, to assay an RFLP locus in three independent F2 progenies, complete cosegregation was obtained with the Ccn-D1 locus. Joint segregation analysis from a genome-wide mapping of RFLP markers and a second CCN resistance in T. tauschii, Ccn-D2, showed this locus to be loosely linked to the proximal region of chromosome 2.Key words: gene targeting, low copy sequences, RAPD, RFLP, bulk segregants.
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Beaver, J. A., and A. F. Iezzoni. "Allozyme Inheritance in Tetraploid Sour Cherry (Prunus cerasus L.)." Journal of the American Society for Horticultural Science 118, no. 6 (November 1993): 873–77. http://dx.doi.org/10.21273/jashs.118.6.873.
Full textAbstract:
Inheritance for seven enzyme loci was determined in seeds produced from crosses and self-pollinations involving four sour cherry parents and one open-pollinated ground cherry (P. fruticosa Pall.) parent. Segregation data were used to identify allozymes and determine whether sour cherry is a naturally occurring allo- or autotetraploid. Three allozymes were identified at the 6-Pgd-1 locus, and two were identified at each of the following loci: Pgi-2, Lap-1, Adh-1, Idh-2, Pgm-2, and 6-Pgd-2. Segregating allozyme patterns for the diagnostic loci Idh-2, Pgm-2, 6-Pgd-1, and 6-Pgd-2 tit disomic inheritance models and thus confirmed the allotetraploid hypothesis for sour cherry. Chi-square tests of independence between loci indicated that Pgi-2, Adh-1, Idh-2, 6-Pgd-1, and 6-Pgd-2 were not linked.
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Khar, Anil, Jernej Jakse, and Michael J. Havey. "Segregations for Onion Bulb Colors Reveal That Red Is Controlled by at Least Three Loci." Journal of the American Society for Horticultural Science 133, no. 1 (January 2008): 42–47. http://dx.doi.org/10.21273/jashs.133.1.42.
Full textAbstract:
Onion (Allium cepa L.) bulb color is controlled by at least five major loci (I, C, G, L, and R) and seedcoat color by one locus (B). The authors developed families segregating for bulb and seedcoat colors, simple sequence repeats (SSRs), and single nucleotide polymorphisms (SNPs) in genomic amplicons of dihydroflavonol 4-reductase (DFR) and anthocyanidin synthase (ANS). The B and C loci were linked to SSRs on chromosomes 1 and 6 respectively. For all of three families, SNPs in DFR cosegregated with the R locus conditioning red bulb color. In the family from B2246 × B11159, red bulbs versus yellow bulbs were controlled by DFR and a locus (L2) linked at 6.3 cM to ANS. The authors propose that yellow bulb onions have been independently selected numerous times and that yellow populations carry independent mutations in structural or regulatory genes controlling the production of red bulb color in onion.
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de Meijer, Etienne P. M., Manuela Bagatta, Andrea Carboni, Paola Crucitti, V. M. Cristiana Moliterni, Paolo Ranalli, and Giuseppe Mandolino. "The Inheritance of Chemical Phenotype in Cannabis sativa L." Genetics 163, no. 1 (January 1, 2003): 335–46. http://dx.doi.org/10.1093/genetics/163.1.335.
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Abstract Four crosses were made between inbred Cannabis sativa plants with pure cannabidiol (CBD) and pure Δ-9-tetrahydrocannabinol (THC) chemotypes. All the plants belonging to the F1’s were analyzed by gas chromatography for cannabinoid composition and constantly found to have a mixed CBD-THC chemotype. Ten individual F1 plants were self-fertilized, and 10 inbred F2 offspring were collected and analyzed. In all cases, a segregation of the three chemotypes (pure CBD, mixed CBD-THC, and pure THC) fitting a 1:2:1 proportion was observed. The CBD/THC ratio was found to be significantly progeny specific and transmitted from each F1 to the F2’s derived from it. A model involving one locus, B, with two alleles, BD and BT, is proposed, with the two alleles being codominant. The mixed chemotypes are interpreted as due to the genotype BD/BT at the B locus, while the pure-chemotype plants are due to homozygosity at the B locus (either BD/BD or BT/BT). It is suggested that such codominance is due to the codification by the two alleles for different isoforms of the same synthase, having different specificity for the conversion of the common precursor cannabigerol into CBD or THC, respectively. The F2 segregating groups were used in a bulk segregant analysis of the pooled DNAs for screening RAPD primers; three chemotype-associated markers are described, one of which has been transformed in a sequence-characterized amplified region (SCAR) marker and shows tight linkage to the chemotype and codominance.
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Zabala, Gracia, and Lila Vodkin. "Cloning of the Pleiotropic T Locus in Soybean and Two Recessive Alleles That Differentially Affect Structure and Expression of the Encoded Flavonoid 3′ Hydroxylase." Genetics 163, no. 1 (January 1, 2003): 295–309. http://dx.doi.org/10.1093/genetics/163.1.295.
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Abstract Three loci (I, R, and T) control pigmentation of the seed coats in Glycine max and are genetically distinct from those controlling flower color. The T locus also controls color of the trichome hairs. We report the identification and isolation of a flavonoid 3′ hydroxylase gene from G. max (GmF3′H) and the linkage of this gene to the T locus. This GmF3′H gene was highly expressed in early stages of seed coat development and was expressed at very low levels or not at all in other tissues. Evidence that the GmF3′H gene is linked to the T locus came from the occurrence of multiple RFLPs in lines with varying alleles of the T locus, as well as in a population of plants segregating at that locus. GmF3′H genomic and cDNA sequence analysis of color mutant lines with varying t alleles revealed a frameshift mutation in one of the alleles. In another line derived from a mutable genetic stock, the abundance of the mRNAs for GmF3′H was dramatically reduced. Isolation of the GmF3′H gene and its identification as the T locus will enable investigation of the pleiotropic effects of the T locus on cell wall integrity and its involvement in the regulation of the multiple branches of the flavonoid pathway in soybean.
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Göçmen, B., Z. Kaya, K. D. Jermstad, and D. B. Neale. "Development of random amplified polymorphic DNA markers for genetic mapping in Pacific yew (Taxusbrevifolia)." Canadian Journal of Forest Research 26, no. 3 (March 1, 1996): 497–503. http://dx.doi.org/10.1139/x26-056.
Full textAbstract:
A genetic linkage map was constructed for Pacific yew (Taxusbrevifolia Nutt.) based on random amplified polymorphic DNA (RAPD) markers. A series of optimization experiments were conducted to develop a highly repeatable protocol for Pacific yew. In these experiments, a high MgCl2 concentration (5.5 mM) together with a low primer concentration (0.2 μm) in the polymerase chain reaction (PCR) mixture yielded the best amplification products. PCR amplification products were further improved by treating the template DNAs with RNase. Experiments showed that bovine serum albumine had the same effect as RNase on PCR amplification. The segregating mapping population consisted of 39 haploid megagametophytes from a single mother tree. DNA extracted from a subset of 6 megagametophytes was screened with 345 ten-base oligonucleotide primers of arbitrary sequence. Of the screened primers, 28% revealed at least one polymorphic locus. Eighty-six of these primers revealed at least one polymorphic locus and were used with the entire set of megagametophyte DNAs. One-hundred-two loci were scored and segregated in the expected 1:1 ratio (1.19 locus per primer). Linkage analysis was conducted using MAPMAKER. Forty-one of 102 markers were distributed into 17 linkage groups and covered 305.8 centimorgans. The remaining 61 unlinked markers should be assigned to linkage groups as more markers are added to the map.
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Arnqvist, Göran, Nikolas Vellnow, and Locke Rowe. "The effect of epistasis on sexually antagonistic genetic variation." Proceedings of the Royal Society B: Biological Sciences 281, no. 1787 (July 22, 2014): 20140489. http://dx.doi.org/10.1098/rspb.2014.0489.
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There is increasing evidence of segregating sexually antagonistic (SA) genetic variation for fitness in laboratory and wild populations, yet the conditions for the maintenance of such variation can be restrictive. Epistatic interactions between genes can contribute to the maintenance of genetic variance in fitness and we suggest that epistasis between SA genes should be pervasive. Here, we explore its effect on SA genetic variation in fitness using a two locus model with negative epistasis. Our results demonstrate that epistasis often increases the parameter space showing polymorphism for SA loci. This is because selection in one locus is affected by allele frequencies at the other, which can act to balance net selection in males and females. Increased linkage between SA loci had more marginal effects. We also show that under some conditions, large portions of the parameter space evolve to a state where male benefit alleles are fixed at one locus and female benefit alleles at the other. This novel effect of epistasis on SA loci, which we term the ‘equity effect’, may have important effects on population differentiation and may contribute to speciation. More generally, these results support the suggestion that epistasis contributes to population divergence.
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Melgar, Sergio, and Michael J. Havey. "The Dominant Ms Allele in Onion Shows Reduced Penetrance." Journal of the American Society for Horticultural Science 135, no. 1 (January 2010): 49–52. http://dx.doi.org/10.21273/jashs.135.1.49.
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The most commonly used source of cytoplasmic male sterility in onion (Allium cepa) is controlled by the interaction of the cytoplasm [male-sterile (S) or normal male-fertile (N)] and one nuclear male-fertility-restoration locus (Ms). Scoring of genotypes at Ms is generally done by testcrossing male-fertile to male-sterile (S msms) plants, followed by scoring of testcross progenies for male-fertility restoration. We identified two N-cytoplasmic families, one that was homozygous dominant and the other segregating at Ms. Plants from each of these two families were individually testcrossed to male-sterile onion. Nuclear restoration of male fertility in testcross progenies was evaluated in the field over 4 years. For male plants homozygous dominant at Ms, we expected testcross families to show 100% male-fertility restoration, but observed mean values between 46% and 100%. For plants segregating at Ms, we again observed lower than expected frequencies of male-fertility restoration. These results demonstrate that the dominant Ms allele shows reduced penetrance, requiring that male-fertility restoration be scored over years to more confidently assign genotypes at Ms.
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Fieldes, M. A., and J. Ross. "Peroxidase activity and relative mobility at anthesis in flax genotrophs and their F2 progeny: developmental and genetic effects." Genome 34, no. 4 (August 1, 1991): 495–504. http://dx.doi.org/10.1139/g91-076.
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The genetic regulation of the environmentally induced heritable difference in peroxidase activity between Durrant's large (L) and small (S) flax genotrophs was examined in leaves from plants ranging in developmental age from 6 days before anthesis to 3 days after. Mean peroxidase activity was higher for S than L and intermediate for the reciprocal F2's from L × S and S × L crosses (F2L × S and F2S × L). However, activity increased with development and, since there were small but significant differences in the average developmental ages of L, S, F2L × S, and F2S × L plants, the effects of development on activity had to be taken into account in examining the F2 activity data for segregation. A regression method was used to remove developmental effects and, underlying these effects, total peroxidase activity appeared to be regulated by a single locus with two alleles and L dominance. Two other dimorphic loci, both described previously, were also examined. One regulates the presence-absence of septa hairs in the seed capsules and the other the relative mobility of anionic peroxidase isozymes. There was no phenotypic linkage between the three segregating parameters. The genetic control of activity appeared to regulate cationic rather than anionic activity. In addition, a relationship between activity and plant height indicated either that peroxidase activity is one of the factors regulating main stem elongation or that the locus regulating peroxidase activity is linked to one of the loci involved in the regulation of plant height.Key words: flax genotrophs, peroxidase, genetic control, development.
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Hemmat, Minou, Susan K. Brown, and Norman F. Weeden. "Tagging and Mapping Scab Resistance Genes from R12740-7A Apple." Journal of the American Society for Horticultural Science 127, no. 3 (May 2002): 365–70. http://dx.doi.org/10.21273/jashs.127.3.365.
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The genetic basis of resistance to apple scab [Venturia inaequalis (Cke.) Wint.] in the Russian apple seedling R12740-7A (Malus Mill. sp.) was investigated. Segregation ratios obtained in crosses with susceptible cultivars suggested that at least two genes were involved, and three foliar resistance reactions (chlorotic, stellate necrotic, and pit type) were observed after inoculation. DNA markers were identified for both the stellate necrotic (Vr) and pit type (no locus designation, Vx suggested) resistance phenotypes. Comparison of resistance phenotypes with marker segregation demonstrated that only two major dominant genes were present in R12740-7A, one producing the stellate necrotic lesion and the other the pit-type lesion. The chlorotic lesion could be attributed to either unclear expression of the resistance phenotype or to susceptible genotypes not contracting the disease. These markers along with a previously published marker for Vf were used to analyze inheritance of resistance in a Vr × Vf cross in advanced breeding material. The markers identified successfully all susceptible progeny, as well as apparent escapes and individuals possessing both Vf and Vr. Thus, the markers should be useful in future screening of segregating progeny and in the pyramiding of scab resistance genes in new cultivars.
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Mamo, Bullo Erena, Kevin P. Smith, Robert S. Brueggeman, and Brian J. Steffenson. "Genetic Characterization of Resistance to Wheat Stem Rust Race TTKSK in Landrace and Wild Barley Accessions Identifies the rpg4/Rpg5 Locus." Phytopathology® 105, no. 1 (January 2015): 99–109. http://dx.doi.org/10.1094/phyto-12-13-0340-r.
Full textAbstract:
Race TTKSK of the wheat stem rust pathogen (Puccinia graminis f. sp. tritici) threatens the production of wheat and barley worldwide because of its broad-spectrum virulence on many widely grown cultivars. Sources of resistance against race TTKSK were recently identified in several barley landraces (Hordeum vulgare subsp. vulgare) and wild barley accessions (H. vulgare subsp. spontaneum). The objectives of this study were to characterize the inheritance of resistance to wheat stem rust race TTKSK in four barley landraces (Hv501, Hv545, Hv602, and Hv612) and two wild barley (WBDC213 and WBDC345) accessions, map the resistance genes, and determine the allelic relationships among the genes in these accessions and the previously described rpg4/Rpg5 locus. Resistant accessions were crossed with the susceptible cv. Steptoe and resulting F3 populations were evaluated for resistance to race TTKSK at the seedling stage. Segregation of F3 families in populations involving the resistance sources of Hv501, Hv545, Hv612, WBDC213, and WBDC345 fit a 1:2:1 ratio for homozygous resistant (HR)/segregating (SEG)/homozygous susceptible (HS) progenies (with χ2 = 2.27 to 5.87 and P = 0.053 to 0.321), indicating that a single gene confers resistance to race TTKSK. Segregation of F3 families in cross Steptoe/Hv602 did not fit a 1:2:1 ratio (HR/SEG/HS of 20:47:43 with χ2 = 11.95 and P = 0.003), indicating that more than one gene is involved in imparting resistance to race TTKSK. Bulked segregant analysis using >1,500 single-nucleotide polymorphism markers positioned a resistance locus in all six populations on chromosome 5HL in very close proximity to the known location of the rpg4/Rpg5 complex locus. Allelism tests were conducted by making crosses among resistant accessions Hv501, Hv545, and Hv612 and also Q21861 with the rpg4/Rpg5 complex. No segregation was observed in F2 families inoculated with race TTKSK, demonstrating that all Hv lines carry the same allele for resistance and that it resides at or very near the rpg4/Rpg5 locus. Phenotype evaluations of the six barley accessions with wheat stem rust race QCCJ revealed resistant infection types (ITs) at a low incubation temperature and susceptible ITs at a high incubation temperature, similar to Q21861, which carries the temperature-sensitive gene rpg4. The accessions also exhibited low ITs against the rye stem rust isolate 92-MN-90, suggesting that they also carry Rpg5. This result was confirmed through molecular analysis, which revealed that all six barley accessions contain the serine threonine protein kinase domain that confers Rpg5 resistance. These results indicate that cultivated barley is extremely vulnerable to African stem rust races such as TTKSK because even these diverse selections of landrace and wild barley accessions carry only one locus for resistance.
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Gale, K. R., J. F. Panozzo, H. A. Eagles, M. Blundell, H. Olsen, and R. Appels. "Application of a high-throughput antibody-based assay for identification of the granule-bound starch synthase Wx-B1b allele in Australian wheat lines." Australian Journal of Agricultural Research 52, no. 12 (2001): 1417. http://dx.doi.org/10.1071/ar01037.
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An enzyme-linked immunosorbent assay (ELISA) for the discrimination of Wx-B1a and Wx-B1b genotypes at the granule-bound starch synthase I (GBSSI) or waxy locus of hexaploid wheat (Triticum aestivum L.) was adapted to a high-throughput, 96-well microtitre plate format. This test is applicable to the direct analysis of starch, flour, or crushed grain and requires less than 1 grain to perform. Several hundred samples may be routinely analysed in one day. The assay was validated using quantitative trait locus (QTL) analysis of a doubled haploid mapping population of the cross Cranbrook (Wx-B1a)/Halberd (Wx-B1b). This demonstrated that the assay unambiguously identified 153 of 161 lines analysed, with a highly significant QTL (LRS value 270) accounting for 83% of ELISA variation, at the Wx-B1 locus on chromosome 4AL. In addition, measurement of total GBSSI variation using a non-isoform-specific GBSSI detection monoclonal antibody also gave a significant QTL (LRS of 84, accounting for 42% of ELISA variation) at the Wx-B1 locus. Application of the assay to crude flour extracts of 8 grains for each of 1093 progeny from 4 crosses segregating at the Wx-B1 locus permitted the unambiguous scoring of lines as pure Wx-B1a or pure Wx-B1b. The scoring by ELISA was strongly related to the flour swelling volume of the lines, thus demonstrating the utility of this high-throughput screening method for the faster, more efficient development of Australian noodle wheats.
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Havey, Michael J., Derek J. Hunsaker, and Eduardo D. Munaiz. "Genetic Analysis of the Unique Epicuticular Wax Profile of ‘Odourless Greenleaf’ Onion." Journal of the American Society for Horticultural Science 146, no. 2 (March 2021): 118–24. http://dx.doi.org/10.21273/jashs05024-20.
Full textAbstract:
The amounts and types of epicuticular waxes on onion (Allium cepa) leaves affect the severity of feeding damage by onion thrips (Thrips tabaci), a serious insect pest of onion. Onion plants with light green leaves are referred to as “glossy” and accumulate less epicuticular wax relative to the blue–green (“waxy”) foliage of wild-type onion. The onion cultivar Odourless Greenleaf (OGL) has visually glossy foliage, shows resistance to thrips feeding damage, and has the unique profile of accumulating waxes with 28 or fewer carbons. Plants of glossy OGL were crossed with the glossy inbred B9885 and waxy inbred lines DH2107, DH066619, and B8667. Hybrid progenies from glossy OGL by waxy plants had waxy foliage, indicating recessiveness of the glossy OGL phenotype relative to the waxy phenotype. Hybrids from the cross of glossy OGL with glossy B9885 were also waxy, revealing different genetic bases for the glossy phenotype in these two onions. Hybrid plants were self-pollinated and segregations in F2 families from OGL × waxy crosses fit the expected 3:1 ratio for the single locus at which the homozygous recessive genotype conditions glossy foliage. Segregations in F2 families from crosses of glossy 9885 × glossy OGL fit the 9:7 ratio, supporting two independently segregating loci, where the recessive genotype at either locus conditions the glossy phenotype. Amounts and types of epicuticular waxes on leaves of F2 progenies from crosses of OGL × waxy B8667 and glossy B9885 × OGL were determined using gas chromatography-mass spectrometry. Single-nucleotide polymorphisms were genotyped and genetic maps were constructed. The visually glossy phenotype from OGL and its unique profile of epicuticular waxes were conditioned by one locus on chromosome 6, for which we propose the name glogl. Onion populations such as OGL with unique epicuticular wax profiles will be important germplasms for the development of onion cultivars that suffer less feeding damage from onion thrips compared with waxy onion.
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Fan, Guiyan, Qianru Wang, Jianfei Xu, Na Chen, Wenwen Zhu, Shaoguang Duan, Xiaohui Yang, et al. "Fine Mapping and Candidate Gene Prediction of Tuber Shape Controlling Ro Locus Based on Integrating Genetic and Transcriptomic Analyses in Potato." International Journal of Molecular Sciences 23, no. 3 (January 27, 2022): 1470. http://dx.doi.org/10.3390/ijms23031470.
Full textAbstract:
Tuber shape is one of the most important quality traits in potato appearance. Since poor or irregular shape results in higher costs for processing and influences the consumers’ willingness to purchase, breeding for shape uniformity and shallow eye depth is highly important. Previous studies showed that the major round tuber shape controlling locus, the Ro locus, is located on chromosome 10. However, fine mapping and cloning of tuber shape genes have not been reported. In this study, the analyses of tissue sectioning and transcriptome sequencing showed that the developmental differences between round and elongated tuber shapes begin as early as the hook stage of the stolon. To fine map tuber shape genes, a high-density genetic linkage map of the Ro region on chromosome 10 based on a diploid segregating population was constructed. The total length of the genetic linkage map was 25.8 cM and the average marker interval was 1.98 cM. Combined with phenotypic data collected from 2014 to 2017, one major quantitative trait locus (QTL) for tuber shape was identified, which explained 61.7–72.9% of the tuber shape variation. Through the results of genotyping and phenotypic investigation of recombinant individuals, Ro was fine mapped in a 193.43 kb interval, which contained 18 genes. Five candidate genes were preliminarily predicted based on tissue sections and transcriptome sequencing. This study provides an important basis for cloning Ro gene(s).
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Armstrong, K. C., S. J. Molnar, and G. Fedak. "Differential transmission of homoeologous chromosomes in heterozygous amphiploids: rRNA loci of Thinopyrum distichum in an amphiploid with Triticum durum." Genome 35, no. 6 (December 1, 1992): 985–91. http://dx.doi.org/10.1139/g92-151.
Full textAbstract:
The segregation of two sets of homoeologous Thinopyrum chromosomes from Th. distichum (5J and 6J) was followed in segregating BC1F2 progeny from the backcross (2n = 42) of the amphiploid of Triticum durum × Th. distichum) (2n = 56) to T. durum (2n = 28). The segregation pattern was followed by the presence or absence of the 18S + 26S rRNA locus using in situ hybridization and Southern analysis of the TaqI digest. The BC1F2 progeny segregated for four to seven NOR chromosomes. This confirmed that one homoeologue carried a nucleolar organizing region (NOR), while in the other it was absent or greatly reduced in copy number. That is, for example, 5J1 and 6J1 carry a NOR site, while 5J2 and 6J2 both lack NORs. Both in situ hybridization and Southern analysis confirmed that presence or absence of NORs did not segregate at random. The NOR on 5J had a 2.9-kb TaqI fragment and this NOR was present in the progeny less frequently than expected. The 6J NOR that carried a 1.1- and 0.8-kb fragment was transmitted to the progeny with a normal frequency. The results are discussed with respect to the implications for creating reconstructed genomes and recovering the genetic variation of a polyploid in addition lines.Key words: segregation, homoeologue, rRNA, amphiploid, polyploid, reconstructed genome, in situ hybridization, TaqI fragment.
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Yamanaka, Naoki, Luciano N. Aoyagi, Md Motaher Hossain, Martina B. F. Aoyagi, and Yukie Muraki. "Genetic Mapping of Seven Kinds of Locus for Resistance to Asian Soybean Rust." Plants 12, no. 12 (June 9, 2023): 2263. http://dx.doi.org/10.3390/plants12122263.
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Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is one of the most serious soybean (Glycine max) diseases in tropical and subtropical regions. To facilitate the development of resistant varieties using gene pyramiding, DNA markers closely linked to seven resistance genes, namely, Rpp1, Rpp1-b, Rpp2, Rpp3, Rpp4, Rpp5, and Rpp6, were identified. Linkage analysis of resistance-related traits and marker genotypes using 13 segregating populations of ASR resistance, including eight previously published by our group and five newly developed populations, identified the resistance loci with markers at intervals of less than 2.0 cM for all seven resistance genes. Inoculation was conducted of the same population with two P. pachyrhizi isolates of different virulence, and two resistant varieties, ‘Kinoshita’ and ‘Shiranui,’ previously thought to only harbor Rpp5, was found to also harbor Rpp3. Markers closely linked to the resistance loci identified in this study will be used for ASR-resistance breeding and the identification of the genes responsible for resistance.
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Dupré, Nicolas, Dominique J. Verlaan, Collette K. Hand, Sandra B. Laurent, Gustavo Turecki, W. Jeptha Davenport, Nicola Acciarri, et al. "Linkage to the CCM2 Locus and Genetic Heterogeneity in Familial Cerebral Cavernous Malformation." Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques 30, no. 2 (May 2003): 122–28. http://dx.doi.org/10.1017/s0317167100053385.
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ABSTRACT:Background:Cerebral cavernous malformation (CCM) is a form of intracranial vascular disease that may arise sporadically or be dominantly inherited. Linkage studies have revealed genetic heterogeneity among the dominantly inherited forms suggesting the existence of at least three loci called CCM1, CCM2 and CCM3.Methods:In the present study, we screened five families with dominantly inherited CCM for CCM1 gene mutations with denaturing high performance liquid chromatography (DHPLC). Then, we performed linkage analysis and haplotyping on these five families using highly polymorphic markers at the candidate CCM loci.Results:None of the five families tested with DHPLC were found to have mutations in the CCM1 gene. Based on haplotyping, we identified three families segregating alleles for CCM2, while two families segregated alleles for CCM3. Using linkage analysis, we could confirm that one family (IFCAS-1) had a positive Lod score of 2.03 (p<0.0001) at the CCM2 locus using marker D7S678.Conclusions:The present study is the first one to replicate linkage at the CCM2 locus and provides a fifth family identified as such. It also supports the concept of genetic heterogeneity in CCM, identifying four other families that showed no mutations in the CCM1 gene.
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Jiang, C., M. E. Lewis, and K. C. Sink. "Combined RAPD and RFLP molecular linkage map of asparagus." Genome 40, no. 1 (February 1, 1997): 69–76. http://dx.doi.org/10.1139/g97-009.
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Two linkage maps of asparagus (Asparagus officinalis L.) were constructed using a double pseudotestcross mapping strategy with restriction fragment length polymorphisms (RFLPs), random amplified polymorphic DNAs (RAPDs), and allozymes as markers in a population generated from crossing MW25 × A19, two heterozygous parents. All data were inverted and combined with the natural data to detect linkages in repulsion phase. Two sets of data, one for each parent, were formed according to the inheritance patterns of the markers. The maternal MW25 map has a total of 163 marker loci placed in 13 linkage groups covering 1281 cM, with an average and a maximum distance between adjacent loci of 7.9 and 29 cM, respectively. The paternal A19 map has 183 marker loci covering 1324 cM in 9 linkage groups, with an average and a maximum distance between two adjacent loci of 7.7 and 29 cM, respectively. Six multiallelic RFLPs segregating in the pattern a/c × b/c and eight heterozygous loci (four RAPDs, and four RFLPs segregating in the pattern a/b × a/b (HZ loci)) were common to both maps. These 14 loci were used as bridges to align homologous groups between the two maps. In this case, RFLPs were more frequent and informative than RAPDs. Nine linkage groups in the MW25 map were homologous to six groups in the A19 map. In two cases, two or more bridge loci were common to a group; thus, the orientation of homologous linkage groups was also determined. In four other cases, only one locus was common to the two homologous groups and the orientation was unknown. Mdh, four RFLPs, and 14 RAPDs were assigned to chromosome L5, which also has the sex locus M.Key words: asparagus, bridge loci, pseudotestcross, RAPD, RFLP, sex expression.
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Lein, Jens Christoph, Katrin Asbach, Yanyan Tian, Daniela Schulte, Chunyan Li, Georg Koch, Christian Jung, and Daguang Cai. "Resistance gene analogues are clustered on chromosome 3 of sugar beet and cosegregate with QTL for rhizomania resistance." Genome 50, no. 1 (January 2007): 61–71. http://dx.doi.org/10.1139/g06-131.
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Worldwide, rhizomania is the most important disease of sugar beet. The only way to control this disease is to use resistant varieties. Four full-length resistance gene analogues (RGAs) from sugar beet (cZR-1, cZR-3, cZR-7, and cZR-9) were used in this study. Their predicted polypeptides carry typical nucleotide-binding sites (NBSs) and leucin-rich repeat (LRR) regions, and share high homology to various plant virus resistance genes. Their corresponding alleles were cloned and sequenced from a rhizomania resistant genotype. The 4 RGAs were mapped as molecular markers, using sequence-specific primers to determine their linkage to the rhizomania resistance locus Rz1 in a population segregating for rhizomania resistance. One cZR-3 allele, named Rz-C, together with 5 other molecular markers, mapped to the Rz1 locus on chromosome 3 and cosegregated with quantitative trait loci for rhizomania resistance. After screening a bacterial artificial chromosome (BAC) library, 25 cZR-3-positive BACs were identified. Of these, 15 mapped within an interval of approximately 14 cM on chromosome 3, in clusters close to the Rz1 locus. Rz-C differentiates between susceptible and resistant beet varieties, and its transcripts could be detected in all rhizomania resistant varieties investigated. The potential of this RGA marker for cloning of rhizomania resistance genes is discussed.
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Yin, Tongming, Xinye Zhang, Minren Huang, Minxiu Wang, Qiang Zhuge, Shengming Tu, Li-Huang Zhu, and Rongling Wu. "Molecular linkage maps of the Populus genome." Genome 45, no. 3 (June 1, 2002): 541–55. http://dx.doi.org/10.1139/g02-013.
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We report molecular genetic linkage maps for an interspecific hybrid population of Populus, a model system in forest-tree biology. The hybrids were produced by crosses between P. deltoides (mother) and P. euramericana (father), which is a natural hybrid of P. deltoides (grandmother) and P. nigra (grandfather). Linkage analysis from 93 of the 450 backcross progeny grown in the field for 15 years was performed using random amplified polymorphic DNAs (RAPDs), amplified fragment length polymorphisms (AFLPs), and inter-simple sequence repeats (ISSRs). Of a total of 839 polymorphic markers identified, 560 (67%) were testcross markers heterozygous in one parent but null in the other (segregating 1:1), 206 (25%) were intercross dominant markers heterozygous in both parents (segregating 3:1), and the remaining 73 (9%) were 19 non-parental RAPD markers (segregating 1:1) and 54 codominant AFLP markers (segregating 1:1:1:1). A mixed set of the testcross markers, non-parental RAPD markers, and codominant AFLP markers was used to construct two linkage maps, one based on the P. deltoides (D) genome and the other based on P. euramericana (E). The two maps showed nearly complete coverage of the genome, spanning 3801 and 3452 cM, respectively. The availability of non-parental RAPD and codominant AFLP markers as orthologous genes allowed for a direct comparison of the rate of meiotic recombination between the two different parental species. Generally, the rate of meiotic recombination was greater for males than females in our interspecific poplar hybrids. The confounded effect of sexes and species causes the mean recombination distance of orthologous markers to be 11% longer for the father (P. euramericana; interspecific hybrid) than for the mother (P. deltoides; pure species). The linkage maps constructed and the interspecific poplar hybrid population in which clonal replicates for individual genotypes are available present a comprehensive foundation for future genomic studies and quantitative trait locus (QTL) identification.Key words: AFLP, Genetic map, poplar, RAPD, SSR.
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Chen, Qijiao, Lianquan Zhang, Zhongwei Yuan, Zehong Yan, Youliang Zheng, Genlou Sun, and Dengcai Liu. "Empirical verification of heterogeneous DNA fragments generated from wheat genome-specific SSR primers." Canadian Journal of Plant Science 88, no. 6 (November 1, 2008): 1065–71. http://dx.doi.org/10.4141/cjps08041.
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Due to the high polymorphisms between synthetic hexaploid wheat (SHW) and common wheat, SHW has been widely used in genetic studies. The transferability of simple sequence repeats (SSR) among common wheat and its donor species, Triticum turgidum and Aegilops tauschii, and their SHW suggested the possibility that some SSRs, specific for a single locus in common wheat, might appear in two or more loci in SHWs. This is an important genetic issue when using synthetic hexaploid wheat population and SSR for mapping. However, it is largely ignored and never empirically well verified. The present study addressed this issue by using the well-studied SSR marker Xgwm261 as an example. The Xgwm261 produced a 192 bp fragment specific to chromosome 2D in common wheat Chinese Spring, but generated a 176 bp fragment in the D genome of Ae. tauschii AS60. Chromosomal location and DNA sequence data revealed that the176 bp fragment also donated by 2B chromosome of durum wheat Langdon. These results indicated that although a single 176 bp fragment was appeared in synthetic hexaploid wheat Syn-SAU-5 between Langdon and AS60, the fragment contained two different loci, one from chromosome 2D of AS60 and the other from 2B of Langdon which were confirmed by the segregating analysis of SSR Xgwm261 in 185 plants from a F2 population between Syn-SAU-5 and Chinese Spring. If Xgwm261 in Syn-SAU-5 was considered as a single locus in genetic analysis, distorted segregation or incorrect conclusions would be yielded. A proposed strategy to avoid this problem is to include SHW’s parental T. turgidum and Ae. tauschii in SSR analysis as control for polymorphism detection. Key words: Synthetic hexaploid wheat, microsatellite, segregation distortion, Xgwm261, transferability
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Esmenjaud, Daniel, Mohamed Youssef Banora, Ulysse Julien-Portier, Maria-Das-Dores Lafargue, Jean-Pascal Tandonnet, Bernadette Rubio, Andrew Walker, Cyril Van Ghelder, and Nathalie Ollat. "A muscadine locus confers resistance to predominant species of grapevine root-knot nematodes (<i>Meloidogyne</i> spp.) including virulent populations." OENO One 57, no. 3 (August 31, 2023): 219–32. http://dx.doi.org/10.20870/oeno-one.2023.57.3.7443.
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Root-knot nematodes (RKNs) Meloidogyne spp. are extremely polyphagous pests and four species severely affect grapevines throughout the world: M. arenaria, M. incognita, M. javanica and M. ethiopica. Californian populations of M. arenaria and M. incognita are reported to be virulent to widely used rootstocks and to the rootstock ‘Harmony’ in particular. Breeding RKNs-resistant grape rootstocks is a promising alternative to highly toxic nematicides. Muscadine (Vitis rotundifolia syn. Muscadinia rotundifolia) is a resistance (R) source with undercharacterised genetics. To this end, we used a segregating progeny between the RKN-resistant Vitis x Muscadinia accession ‘VRH8771’ from the muscadine source ‘NC184-4’ and the RKN-susceptible V. vinifera cv. Cabernet-Sauvignon. We first phenotyped its resistance to isolates of the i) M. arenaria, ii) M. incognita and iii) M. javanica species, and then to iv) two mixed Harmony-virulent Californian populations of M. arenaria and M. incognita. Finally, we created an isolate of M. arenaria and M. incognita from these Harmony populations and phenotyped the progeny to each of them [v) and vi)], and to vii) an isolate of M. ethiopica. The resistance phenotype of all the progeny’s individuals was independent of the RKN isolates or populations used. Resistance was mapped in a region of chromosome 18 in VRH8771, supporting the hypothesis that it is conferred by a single gene with an unprecedented wide spectrum in grapevine, including Harmony-virulent isolates. This dominant gene, referred to as MsppR1, is linked to the telomeric QTL XiR4 for X. index resistance from the same source. Additionally, plant mortality data showed that MsppR1-resistant material expressed a high-level resistance to the Harmony-virulent isolates. Our results are a first step towards the development of marker-assisted breeding using SSR and SNP markers for resistance to RKNs in accession VRH8771.
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Filatov, Dmitry A., and Deborah Charlesworth. "DNA Polymorphism, Haplotype Structure and Balancing Selection in the Leavenworthia PgiC Locus." Genetics 153, no. 3 (November 1, 1999): 1423–34. http://dx.doi.org/10.1093/genetics/153.3.1423.
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Abstract A study of DNA polymorphism and divergence was conducted for the cytosolic phosphoglucose isomerase (PGI:E.C.5.3.1.9) gene of five species of the mustard genus Leavenworthia: Leavenworthia stylosa, L. alabamica, L. crassa, L. uniflora, and L. torulosa. Sequences of an internal 2.3-kb PgiC gene region spanning exons 6–16 were obtained from 14 L. stylosa plants from two natural populations and from one to several plants for each of the other species. The level of nucleotide polymorphism in L. stylosa PgiC gene was quite high (π = 0.051, θ = 0.052). Although recombination is estimated to be high in this locus, extensive haplotype structure was observed for the entire 2.3-kb region. The L. stylosa sequences fall into at least two groups, distinguished by the presence of several indels and nucleotide substitutions, and one of the three charge change nucleotide replacements within the region sequenced correlates with the haplotypes. The differences between the haplotypes are older than between the species, and the haplotypes are still segregating in at least two of five species studied. There is no evidence of recent or ancient population subdivision that could maintain distinct haplotypes. The age of the haplotypes and the results of Kelly's ZnS and Wall's B and Q tests with recombination suggest that the haplotypes are maintained due to balancing selection at or near this locus.
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Zhang, Yiping, and John R. Stommel. "Identification of PCR-based Molecular Markers Linked to B, A Carotenoid-related Gene in Tomato." HortScience 33, no. 3 (June 1998): 515c—515. http://dx.doi.org/10.21273/hortsci.33.3.515c.
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β-carotene is the principal provitamin A caroteniod found in tomato fruits and makes a significant contribution to the fruits nutritional value. The dominant B gene conditions high levels of β-carotene in ripe tomato fruits. PCR-based molecular markers, including random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP), were used to identify marker linkage to the B locus. The study was conducted using a near-isogenic line (NIL) of the cultivar Rutgers isogenic for the B locus and bulk segregant analysis of an interspecific F2 population segregating for the B locus, which was derived from the cross of Lycopersicon cheesmanii accession LA 317 × L. esculentum cv. Floradade. Sixty-four AFLP primer pairs and 1018 arbitrary RAPD primers were screened for polymorphism between the pair of NILs and between the two bulks. A number of amplified RAPD and AFLP products were identified that were present in one line or bulk but not the other. Marker linkage with the B locus was confirmed by checking individual samples from the F2 and BC populations. Two RAPD markers were confirmed tightly linked with the B phenotype using the interspecific F2 population. Similarly, a single AFLP marker was identified with close linkage to the B phenotype using the NIL F2 population. The markers identified in this study can be useful in breeding programs with marker assisted selection and, if very tightly linked, as a starting point to isolate the gene.
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Summerbell, R. C., A. J. Castle, P. A. Horgen, and J. B. Anderson. "Inheritance of restriction fragment length polymorphisms in Agaricus brunnescens." Genetics 123, no. 2 (October 1, 1989): 293–300. http://dx.doi.org/10.1093/genetics/123.2.293.
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Abstract The cultivated mushroom, Agaricus brunnescens, is secondarily homothallic; most basidia produce only two basidiospores, each of which receives two of the four post meiotic nuclei. The segregation of restriction fragment length polymorphisms (RFLPs) detected by four plasmid probes carrying single-copy nuclear DNA of Agaricus was followed in seven parental strains including commercial, wild-collected, and artificially synthesized heterokaryons. Of a total of 367 single-spore progeny examined, 351 (95.6%) were heteroallelic at all RFLP loci heteroallelic in the respective parents. Of the 16 segregant isolates, ten (2.7% of the total) were homoallelic at all segregating loci assayed, suggesting that these isolates were most probably derived from rare spores that had received only a single postmeiotic nucleus. Some of these ten isolates had recombinant genotypes. Only five isolates (1.4% of the total) showed homoallelism at one of the loci heteroallelic in the parent, while remaining heteroallelic at other loci. These five genotypes suggest that a crossover had occurred between a marker locus and its respective centromere. Taken together, the results suggest that meiosis in A. brunnescens is accompanied by low levels of recombination and that nonsister nuclei are preferentially incorporated into basidiospores after meiosis II.
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Weeden, N. F., and R. W. Robinson. "ALLOZYME SEGREGATION RATIOS IN THE INTERSPECIFIC CROSS CUCURBITA MAXIMA x C. ECUADORENSIS SUGGEST THAT HYBRID BREAKDOWN IS NOT CAUSED BY MINOR ALTERATIONS IN CHROMOSOME STRUCTURE." Genetics 114, no. 2 (October 1, 1986): 593–609. http://dx.doi.org/10.1093/genetics/114.2.593.
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ABSTRACT The parentals of the interspecific cross Cucurbita maxima ×C. ecuadorensis had different isozyme phenotypes for 12 enzyme systems. Characterization of the systems demonstrated that the expression and intracellular distribution of the isozymes were similar to those in other plant taxa; however, a considerable number of duplicate loci were identified, indicative of a polyploid ancestry for Cucurbita. Genetic analysis provided evidence for 20 loci segregating in F2 and backcross populations. Five linkage groups were identified, consisting of the loci Aat-mb - - Mdh-m2; Gal-1 - - Gal-2; Aat-p2 - - Gpi-c2; Acp-1 - - Pgm-c2 - - Pgm-p; and Est-1 - - Tpi-c2. Significant deviations from Mendelian segregation ratios were observed in 14% of the data sets for individual loci. However, these instances were scattered among the loci, no single locus consistently displaying skewed ratios. Recombination frequencies between linked loci were similar to those observed in intraspecific crosses, and the ratio of heterozygous to homozygous genotypes in backcross populations was very close to one. These results suggest that small differences in chromosome structure were not the major cause of the loss of fertility observed in F2 and backcross populations.