Tesi sul tema "Hybridisation"
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1
Gosden, Jane Louise. "What prevents hybridisation in Celmisia?" Thesis, University of Canterbury. Biological Sciences, 2012. http://hdl.handle.net/10092/7615.
Testo completoAbstract (sommario):
Hybrids are common, being found in about 25% of all plant species, but the isolating barriers which
preserve species integrity are poorly studied. I investigated this question in the large New Zealand
genus Celmisia Cass. (Asteraceae), which hybridises readily in cultivation, but wild hybrids are
relatively rare. My study quantitatively tests four potential reproductive isolating barriers in 12
sympatric species of Celmisia found in the Craigieburn Range, inland Canterbury, New Zealand. I
examined two potential prezygotic reproductive isolating barriers (flowering phenology and pollinator
specialisation), and two potential postzygotic barriers (pre-dispersal seed predation and hybrid seed
germination). I used null models to test whether Celmisia species had temporally segregated
flowering times, and found that some Celmisia are temporally segregated and thus less likely to form
hybrids. I used experimental pair-wise flowering arrays to observe insect visitation to six different
Celmisia species pairs. While I found no difference in the overall pollinator community, several insect
families showed preferences for some Celmisia species. Furthermore, I found that subtle floral
character differences were driving these insect preferences. In particular, I found scape height to be
positively associated with insect visitation with taller Celmisia being favoured over shorter species.
Insect preferences did not translate into strong floral constancy, therefore indicating that Celmisia
flower visitors are likely to be a weak barrier to hybridisation. I reared a range of insect seed predators
from field-collected capitula of the hybrid C. x pseudolyallii and both parent species (C. lyallii and C.
spectabilis). There was no overall difference in the number of seed-predators per capitulum between
hybrid and parent Celmisia taxa. I collected and sowed seeds from three Celmisia hybrids and their
parent species in order to test whether hybrids were less fertile than their parent species. I found no
evidence to suggest that the seeds of hybrids had lower germination success than those of their
parents. Overall I found evidence for only weak prezygotic reproductive isolation and no evidence for
postzygotic isolation in the four barriers I examined in Celmisia.
2
Al-Atabee, Jabbar Selman Khilbas. "Somatic hybridisation of ornamental Compositae". Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235961.
Testo completo
3
Barr, S. N. R. "Potato improvement by somatic hybridisation". Thesis, University of Dundee, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311573.
Testo completo
4
Bentall, Robert D. "Genre hybridisation in electroacoustic composition". Thesis, Queen's University Belfast, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.680889.
Testo completo
5
Siamasonta, Bruce M. "Interspecific hybridisation in the genus Lupinus". Thesis, University of Reading, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319252.
Testo completo
6
Tombelli, Sara. "Piezoelectric and optical detection of hybridisation". Thesis, Cranfield University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341055.
Testo completo
7
McKenzie, Robert James. "Intergeneric hybridisation in New Zealand Gnaphalieae (Compositae)". Thesis, University of Canterbury. Botany, 2001. http://hdl.handle.net/10092/4844.
Testo completoAbstract (sommario):
The occurrence of natural intergeneric hybridisation among the New Zealand Gnaphalieae was investigated using a case study approach. Putative hybrids between Anaphalioides bellidioides and Ewartia sinclairii were collected from beside the Yeo Stream, Inland Kaikoura Range, Marlborough and putative hybrids between Leucogenes grandiceps and Raoulia eximia from Mount Hutt, Mount Hutt Range, Canterbury. Cytology, pollen stainability and experimental crosses provided evidence for reduced fertility in the putative hybrids. Field evidence and the morphology and leaf anatomy of the putative hybrids supported the hybridity hypotheses for the majority of the putative hybrids. A range of isolating mechanisms may restrict the frequency of these hybrids in the field. In particular, environmental factors (the availability of suitable habitats and natural disturbance) and pre-zygotic and post-zygotic barriers (embryo and/or endosperm abortion, hybrid fitness and hybrid fertility) were suggested to be important. Cross-compatibility among indigenous Gnaphalieae and with related exotic Gnaphalieae was
investigated through artificial crosses. Individual plants from six indigenous and five exotic
species were preferentially selected as parents. The results provided evidence for the cross compatibility
of many indigenous Gnaphalieae, including species of Anaphalioides, Euchiton,
Ewartia, Helichrysum , Leucogenes and Raoulia. A plant of Euchiton audax was cross-compatible
with individual plants of Ewartia planchonii and Gamochaeta spicata. The results
indicate species groups among the indigenous Gnaphalieae are less genetically distinct than
morphology suggests. The partial fertility of some natural intergeneric hybrids suggests
intergeneric gene exchange has a potential role in the future evolution of the group.
8
Chapman, J. V. "Intergeneric somatic hybridisation studies in the Solanaceae". Thesis, University of Nottingham, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374682.
Testo completo
9
Fish, Neil William. "Somatic hybridisation of potato (Solanum tuberosum L.)". Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47062.
Testo completo
10
Che, Zainal Abidin Nik Mohd Farid. "Hybridisation of Bees Algorithm for continuous optimisation". Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8240/.
Testo completoAbstract (sommario):
This research introduces two different methods that are Levy Flight and Hooke and Jeeves to the Bees Algorithm with the aim of improving the convergence speed and its robustness. Both methods are incorporated to the Bees Algorithm at neighbourhood search of the elite bees since that particular locations are the most promising area during optimisation process. Each Bees Algorithm and the newly incorporated method with thirteen different parameter settings are subjected to fifteen different benchmark test functions. These benchmark test functions are represented with different characteristics in terms of its differentiability, separability, scaleability, and modality. Bees Algorithm with Levy-flight method incorporated to the local search performs excellent result for 13 out of 15 functions against standard Bees Algorithm in terms of its success rate and convergence speed in which it is validated by the statistical T test. As a matter of fact, the new method indicates better robustness for 13 functions in terms of achieving good result for solving different types of optimisation problems. For the Bees Algorithm with Hooke and Jeeves method, the new approach reaches a relatively better performance compared with standard Bees Algorithm in which one parameter excels at reaching optimum solution for most of the test functions.
11
Curran, Arran. "Exciton-photon hybridisation in ZnSe based microcavities". Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2169.
Testo completoAbstract (sommario):
This thesis presents the design, fabrication and experimental analysis of ZnSe based microcavities. Semiconductor microcavities are micro-structures in which the exciton ground state of a semiconductor is coupled to a photonic mode of an optical cavity. The strong light matter coupling mixes the character of excitons and photons, giving rise to the lower and upper cavity polaritons, quasiparticles with an unusual dispersion due to the extreme mass contrast between the composite exciton and photon. In particular, the dispersion of the lower polariton forms a dip around the lowest energy state with zero in-plane momentum. In this dip, which can be seen as a trap in momentum space, the polaritons are efficiently isolated from dephasing mechanisms involving phonons. The features of these quasiparticles promise a variety of applications, for instance lasing without inversion and micro-optical parametric amplifiers, and an environment to study fundamental physics, such as Bose-Einstein condensation in the solid state. By overcoming the longstanding fabrication problems of ZnSe-based microcavities, the enlarged exciton binding energy in combination with the use of highly reflective dielectric mirrors makes this material system ideally suited to the realisation of polariton-based devices operating at room temperature. An epitaxial liftoff technology is developed that relies on the high etch selectively between the ZnSe heterostructure and a novel II-VI release layer, MgS. Three hybrid microcavities are fabricated with the liftoff technique and spectroscopically characterised. Angle resolved transmission experiments reveal strong hybridization of the ZnSe/Zn0:9Cd0:1Se quantum well excitons and cavity photons in a fixed microcavity. A completely length tunable microcavity is presented and shown to exhibit similar dispersion as for the fixed microcavity, with the addition of evidencing the cavity polariton bottleneck effect. The nonlinear optical features are discussed. Photoluminescence data is presented that evidences the first observation of the build up of cavity polaritons at the edge of the momentum space trap in the lower polariton branch, the bottleneck effect, in a ZnSe based microcavity. Finally, lasing at room temperature in the blue spectral region is presented for a metal/dielectric hybrid microcavity.
12
Selver, Erdem. "Tow level hybridisation for damage tolerant composites". Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/tow-level-hybridisation-for-damage-tolerant-composites(8cf53f8c-165f-4e8b-b67f-f8fd34c327e2).html.
Testo completoAbstract (sommario):
Fibre reinforced composites have higher specific strength and stiffness in comparison to metals. However, composites are susceptible to impact damage resulting in degradation of mechanical properties especially compression strength. Numerous studies have been conducted to improve the impact damage tolerance of composite laminates using modified resin systems, thermoplastic matrices, 3-D fibre architectures and through thickness reinforcement. This work is primarily focussed on incorporating non dissolvable polypropylene fibres (PP) in a thermoset matrix for improving the damage tolerance. Commingling and wrapping techniques have been investigated. PP fibres have been incorporated at the preform stage and hence do not adversely affect the viscosity of the resin during infusion. The healing effect of PP fibres on impact damaged composite laminates when heating is introduced has also been studied. High velocity impact test results showed that using commingled glass/PP fibres increased the total energy absorption of composite laminates by 20% due to the extensive plastic deformation of the PP fibres and through the use of toughening mechanisms in the form of resin cracking and delamination. It has been found that PP fibres provide protection to the glass fibres during low velocity impact loading, so fewer fibre breakages occur which lead to improved residual properties compared with pristine glass laminates. Compression after impact (CAI) tests showed that the residual strength as a percentage of non-impacted strength increased with percentage of PP fibres used. For impact of 20-50J, glass/epoxy laminates retained 32 45% of their compressive strength while laminates with 7%, 13% and 18% PP fibres retained 37 50%, 42-52% and 43-60% of their compressive strength, respectively. It was also observed that glass/PP woven laminates had better compressive strength retention (62 83%) than the glass/PP non-crimp laminates (37-50%). Composite laminates with high-modulus PP fibres (Innegra) exhibited higher residual compression strengths in comparison to laminates with lower modulus PP fibres. For 15-50J impact, glass/Innegra laminates showed residual compression strength of 50 63% in comparison to 39-60%; laminates without thermoplastic fibres exhibited 33 43% residual compression strength. Modulus of thermoplastic fibres appears to be important at higher energy levels. Healing of damaged commingled laminates produced a significant reduction in the damage area and a corresponding increase in CAI strength after heating at 200ºC; CAI strength of healed laminates is about 85% of undamaged samples in comparison to 60% for non-healed samples. A novel micro-wrapping technique, developed in this work, demonstrated significant reduction in damage area (46%) in comparison to the commingling method. Core wrapped laminates had higher residual strength (43-60%) than glass laminates (33-43%). Better PP distribution in core-wrapped composites helped to decrease the PP rich areas and the impact damage did not propagate easily in comparison to commingled composites. However due to the reduction in damage area, impact energy absorption in core wrapped laminates was lower than for commingled.
13
Hao, Danni. "Hybridisation of plasmonic and acoustic biosensing devices". Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/8992/.
Testo completoAbstract (sommario):
Monolithically integrating multiple sensing technologies shows a great potential to perform quantitative measurements for multiple biomarkers of diseases and also provide more insight towards one single biochemical event. The localised surface plasmon resonance spectroscopy measures the change in the refractive index arising from the molecular adsorption on the metallic nanostructures. Acoustic sensors, such as surface acoustic wave sensor and quartz crystal microbalance, measure the variation of its mechanical oscillation caused by the sum of the deposited molecules and the solvent coupled to the adsorbed molecules. Both techniques are known independently as having applications in in-situ, label-free sensing and analysis of biological binding reactions. Due to their complementary properties, the integration of both can prove to be a valuable tool for studying biomolecules on sensing surface. This thesis reports on the development of a hybrid biosensing device that integrates localised surface plasmonic sensing and acoustic sensing technologies. Gold nanodisk arrays as localised surface plasmon resonance sensing device was studied in visible region using three substrates: borosilicate glass, lithium niobate and quartz. The design, simulation, fabrication and characterisation of the gold nanodisk arrays, and the sensing performance optimisation were investigated using glass substrate. Lithium niobate, as a piezoelectric material has surface acoustic wave compatibility and this study can pave the way towards the development of hybrid sensing devices. The study on lithium niobate demonstrated the feasibility of a localised surface plasmon resonance device utilising a high refractive index, birefringent and piezoelectric substrate. Using quartz as the substrate, the design and fabrication of a hybrid sensor were performed, which integrated localised surface plasmonic resonance into a quartz crystal microbalance for studying biochemical surface binding reactions. The coupling of localised plasmon resonance nanostructures and a quartz crystal microbalance allows optical spectra and quartz crystal microbalance resonant frequency shifts to be recorded simultaneously, and analysed in real time for a given surface adsorption process. This integration has the potential to be miniaturised for application in point-of-care diagnostics.
14
Köllensperger, Peter Andreas. "Label-free detection of DNA hybridisation using SERS". Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441415.
Testo completo
15
Lenaerts, Jeremy. "Molecular beacons as hybridisation probes in microbial ecology". Thesis, University of Exeter, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493638.
Testo completoAbstract (sommario):
Microorganisms are of fundamental importance to global biogeochemical cycling, yet aspects of their ecology are poorly understood. Within the present methods used to study microbial ecology are limitations with regards to sensitivity, applicability and automation. This study aimed to investigate the potential application of novel nucleic acid probes (molecular beacons and locked nucleic acid probes) in microbial ecology.
16
Lee, Cheol Hee. "Somatic and gametosomatic hybridisation in the family Solanaceae". Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329842.
Testo completo
17
Ghaffari, Saeed R. "Development and application of comparative genomic hybridisation (CGH)". Thesis, University of Glasgow, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390763.
Testo completo
18
Seear, Paul James. "Protoplast production and interspecific hybridisation in Lupinus albus". Thesis, University of Reading, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326751.
Testo completo
19
Silva, Tara. "Intergeneric hybridisation between Fragaria vesca and Potentilla fruticosa". Thesis, University of Reading, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252714.
Testo completo
20
Chubb, Tanya L. A. "Phylogeography and Hybridisation of the New Zealand House Mouse". The University of Waikato, 2008. http://hdl.handle.net/10289/2479.
Testo completoAbstract (sommario):
Three subspecies of house mice of different geographic origins have reached New Zealand; M. m. domesticus (10 haplotypes), M. m. musculus (1 haplotype) both from Europe, and M. m. castaneus (3 haplotypes) from Asia. Identifying the sources of the multiple historical introductions of the house mouse is a complex issue, particularly during the peak colonisation period of 1830-1880. The early European settlers came with many bags, crates, plants, seed and livestock, which provided ample travel opportunities for stowaway rats and mice. With the assistance of volunteers, I have collected mice from various locations throughout the New Zealand region, to confirm the previously recorded haplotypes and to look for evidence of hybridisation between the colonising subspecies. Morphological characteristics traditionally used for identification of subspecies were compared with genetic characters, to establish whether the use of morphology is still a viable method of identifying subspecific distinctions between mice in New Zealand. While no M. m. musculus haplotypes were found among these samples, some mice still had the coat colouration typical of M. m. musculus. Data from mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) markers revealed some surprising results. I have found six new M. m. domesticus haplotypes, and three new M. m. castaneus haplotypes. The data have also revealed extensive hybridisation, particularly between M. m. domesticus and M. m. castaneus. The finding of the new haplotypes supports the previous assumption that there were multiple introductions of mice into New Zealand, but the finding of M. m. castaneus in inland towns and cities does not support the associated assumption that European mice were initially the only mice present in New Zealand. Rather, the wide distribution of M. m. castaneus suggests that this subspecies probably arrived during the early nineteenth century. The house mouse has long been recognised as an ideal organism for hybridisation studies, and the finding of a hybrid zone within New Zealand would provide an excellent opportunity to extend our knowledge of hybridisation and gene transfer. Previous studies found M. m. domesticus in Napier, and a M. m. musculus/M. m. castaneus hybrids in Wellington. A systematic sampling programme was undertaken between Wellington and Napier following State Highway 2 (SH2), in an attempt to locate a hybrid zone. Analysis of mtDNA and nDNA showed that, M. m. castaneus was found as far North as Dannevirke, and M. m. domesticus as far South as Featherston. There was also extensive evidence of integration of M. m. domesticus nDNA markers into mice with M. m. castaneus mtDNA. There was no clear support for a hybrid zone, but this does not mean that one has not existed in the past and that it has since been overrun by movement of mice with humans and their goods. Identification of subspecies by morphological characteristics, while used with confidence in other countries, is of little use in New Zealand. Extensive hybridisation/and or introgression between the subspecies has long since blurred any morphological distinctions the colonising mice may have had. I propose that these physical characters should be used in support of genetic analysis of the subspecies. The official classification of the New Zealand house mouse currently stands as M. m. musculus, however, data collected does not support this and it is proposed that the official classification should be changed to M. m. domesticus.
21
Narayanan, Sukunath. "Chemically modified oligonucleotides as hybridisation probes and immunostimulatory agents /". [S.l. : s.n.], 2004. http://www.gbv.de/dms/bs/toc/481721770.pdf.
Testo completo
22
Hollingsworth, Michelle Louise. "Clonal growth and hybridisation in some invasive Fallopia spp". Thesis, University of Leicester, 1998. http://hdl.handle.net/2381/10204.
Testo completoAbstract (sommario):
Molecular markers have been used to examine the population biology and dynamics of hybridisation in Britain, of some invasive weeds from the genus Fallopia: F. japonica var. japonica and F. sachalinensis. Both species are gynodioecious, but in Britain, only female plants of F. japonica var. japonica are present. Molecular studies using RAPDs (randomly amplified polymorphic DNA) suggest that the entire British population of this taxon consists of a single genet. The same genotype has also been recovered in all samples examined from Europe and North America. F. sachalinensis. on the other hand, showed higher levels of clonal diversity consistent with sexual reproduction. The two species hybridise in Britain, and the hybrid (Fallopia x bohemica) shows partial to full fertility. High levels of clonal diversity were detected using RAPDs and inter-SSRs (inter-simple sequence repeats), probably reflecting a combination of multiple origins and hybrid fertility. A study of chloroplast RFLPs (restriction fragment length polymorphisms) has shown that the mode of chloroplast inheritance appears to be predominantly maternal, and Fallopia japonica var. japonica is the female parent of all of its hybrids. Based on RAPD data, evidence for backcrossing between Fallopia x bohemica and F. japonica var. japonica was detected at two sites. Flowering material at one site showed the putative backcross to be male fertile. Such plants are of interest as they are possible intermediate steps in the acquisition of genes restoring male fertility to F. japonica var. japonica. The ability of an already invasive species to reproduce and disperse by seed as well as by vegetative propagation, may serve to enhance its invasive capabilities. Molecular data based on chloroplast trnL intron sequences and RAPDs support previous morphological evidence that introduced material of at least Fallopia japonica var. japonica is different from Asiatic stock.
23
Nosrati-Koloujeh, Houshang. "Apomixis, hybridisation, polyploidy and crossability in the genus Fragaria". Thesis, University of Aberdeen, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430057.
Testo completoAbstract (sommario):
The relationship of parental genetic distance with cross success and progeny fitness was investigated in crosses made within diploid Fragaria. The mean values for all three components of success rate of crosses (measured as berry set, achene set and seed germination) at intra- and interspecific levels were not correlated with parental genetic distance. While mean berry set and seed germination at cross types was not affected by parental genetic distance, mean achene set was higher in crosses with intermediate genetic distance and lower in crosses between both more closely and more distantly related taxa, suggesting both inbreeding and outbreeding depression effect on achene set. Three components of progeny fitness (assessed as progeny flowering frequency, berry set and pollen sterility) were strongly correlated with parental genetic distance in both intra- and interspecific crosses. By increasing parental genetic distance, flowering frequency and berry set consistently decreased while pollen sterility increased. Therefore, outbreeding depression has strongly affected all three components of progeny fitness. Marked outbreeding depression was evident on flowering frequency and berry set at very short genetic distances between subspecies, and even within subspecies at forma levels, while it was not evident in pollen sterility of progeny at short genetic distance within subspecies. Highly male sterile plants were found among progeny from crosses within F. vesca ssp. Vesca. As the plants had high levels of berry set, the occurrence of high male sterility among progeny from more closely related taxa could be interpreted as a result of hermaphroditism suppression and evidence of a trend towards gynodioecy in this taxon.
24
Liley, Martha Jane. "Surface plasmon resonance for the detection of DNA hybridisation". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357824.
Testo completo
25
Bolbol, Ahmed A. E. "Genetic analysis of postzygotic hybridisation barriers in Arabidopsis thaliana". Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.537702.
Testo completoAbstract (sommario):
Most studies of plant hybridisation are concerned with documenting its occurrence in different plant groups. Many flowering plants are polyploids and seeds developed from crosses between individuals of different ploidies usually show abnormal features and often abort. The success or failure of interploidy crosses is very important to understanding the evolution of plants as well as to agriculture, but much remains to be learned about the nature of hybridisation barriers. Several mechanisms have been proposed to explain postzygotic barriers, including negative interactions between diverged sequences, global genome rearrangements, and widespread epigenetic reprogramming. Some recent advances in our understanding of the process of hybridisation are derived from different experimental studies on a series of A. thaliana ecotypes. Crosses between diploid (2x) and tetraploid (4x) individuals of the same ecotype can result in F1 lethality, and this dosage-sensitive incompatibility plays a major role in polyploidy speciation research. We have performed interploidy crosses between different diploid maternal A. thaliana ecotypes and tetraploid paternal Col-0 ecotype and identified a genetic variation in F1 lethality. We also found that maternal parents of some ecotypes such as Tsu-1 suppressed the F1 lethality caused by paternal-excess interploidy cross of Col-0 ecotype. A preliminary mapping exercise produced advanced backcross populations that are suitable for mapping maternal modifiers and for the identification of modifier genes. Furthermore, we studied the killer effect caused by Col-0 and identified three additive QTL that affect the rate of postzygotic lethality in F1 during interploidy crosses. This information will facilitate the identification of paternal genes that cause F1 lethality and contribute to reproductive isolation. The moa-1 (mosaic aneuploidy 1) mutant of A. thaliana was obtained in a screen of chemically (EMS) mutagenised seeds of Landsberg erecta (Ler). moa-1 has various phenotypic differences to wild type; the preliminary karyotype analysis showed that the cells of individual moa-1 mutant plants have a variable number of chromosomes (usually between 11-18). In contrast, the cells of wild type Arabidopsis plants and conventional aneuploids have a fixed number of chromosomes in each somatic cell. This data showed that all moa-1 plants have an abnormal number of chromosomes and thus they were termed as mosaic aneuploids.
26
Ward, Benjamin. "The role of recombination and hybridisation in adaptive evolution". Thesis, University of East Anglia, 2017. https://ueaeprints.uea.ac.uk/63187/.
Testo completoAbstract (sommario):
As one of the five evolutionary forces, recombination fulfills both a cleansing role, as well as a role in generating genetic diversity. Recombination cleanses by separating deleterious mutations from their genomic background, increasing the efficacy of purifying selection and curtailing the continuous accumulation of deleterious mutations. Recombination also plays a fundamental role in the repair of damaged DNA, and it can be a creative force, resulting in the formation of novel genotypes, haplotypes and alleles, thereby playing a key role in adaptive evolution. By uniting beneficial mutations that exist at different loci in separate lineages, meiotic recombination during sex accelerates adaptive evolution. Although recombination leaves a distinct signature or footprint in the genome of organisms, identifying this force can be difficult; subsequent recombination events tend to wipe out their past genomic footprints. This thesis presents the development of a novel software package called HybridCheck, for the detection of genomic regions affected by recombination in Next Generation Sequence data, and the rapid molecular dating of recombination events. Hybrid-Check was used to analyze recombination signal in different races of the plant pathogen Albugo candida, a generalist obligate biotroph that infects Brassica plants. I show that recombination facilitated occasional introgression and gene flow between host-specialized races. This may have accelerated the rate of adaptive evolution, and possibly broadened v the pathogen’s host-range. Finally, the genome of the polar diatom Fragilar- iopsis cylindrus contains diverged alleles that are differentially expressed in different environmental conditions. The hypothesis that ancient asexuality explains how the diverged alleles evolved is challenged, but not rejected, based on evidence of recombination presented in this thesis. An alternative hypothesis is proposed: allelic divergence might have evolved despite the homogenizing effect of meiotic recombination as a result of very large effective population sizes and strong diversifying selection on F. cylindrus in the polar environment.
27
O'Brien, Daniel. "Heroic masculinities : evolution and hybridisation in the peplum genre". Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/367195/.
Testo completoAbstract (sommario):
My area of research is the peplum, a cycle of mythological action films produced in Italy from 1957 to 1965, and its influence on both contemporaneous and subsequent filmic depictions of mythical heroes. I argue that this genre is a significant cinematic form which has been marginalised in the fields of film and cultural studies. My thesis reassesses the peplum in terms of its representations of heroic masculinity and the ways in which these relate to wider debates on masculinity. Critics such as Richard Whitehall (1963), Gianni Rondolino (1979) and Richard Dyer (1996, 1997) have noted that the cycle began with Le fatiche di Ercole (Hercules, Pietro Francisci, 1958), which established the peplum ground rules. Taking this film as my starting point, I trace the evolution of the genre through a series of case studies, including Romolo e Remo (Duel of the Titans, Sergio Corbucci, 1961), which offers contrasting forms of heroic masculinity, and counter representations of Herculean masculinity in Jason and the Argonauts (Don Chaffey, 1963), an American production made partly in response to the success of the peplum, and Ercole alla conquista di Atlantide (Hercules Conquers Atlantis, Vittorio Cottafavi, 1961). I also discuss later reconfigurations of the peplum hero in the American-financed Conan the Barbarian (John Milius, 1982) and 300 (Zack Snyder, 2007), which draw on the iconography and aesthetics of the peplum to markedly different effect. Previous peplum scholarship has characterised the genre as endorsing the value of white male physical strength in the context of a reactionary patriarchal status quo. I argue that the depiction of masculinity in these films is more varied, problematic and contradictory than this over-generalised reading would suggest. It is my contention that the peplum’s diverse representations of masculinity offer a notable contribution to ongoing debates on maleness as centred on and expressed by the body—within film studies, academia and the wider culture—that has been largely unexplored and unappreciated. My re-evaluation of the peplum also underlines the cultural value of Italian and indeed European genre cinema, fields still overshadowed in film studies by the dominant Hollywood models.
28
Whitaker, Noel James. "Somatic cell hybridisation analysis of SV40-immortalised human cells". Thesis, The University of Sydney, 1991. https://hdl.handle.net/2123/26432.
Testo completoAbstract (sommario):
Immortalisation is an important aspect of cancer cell biology. Whereas normal diploid mammalian cells have a finite lifespan in culture [Hayflick and Moorhead, 1961], tumours often contain cells that exhibit an apparently unlimited proliferative potential. In many experimental systems immortalisation appears to be an obligatory prerequisite for the induction of tumours [e.g. Newbold and Overell, 1983; O'Brien et al., 1986; Reddel et al., 1988b]. Human cells rarely, if ever, spontaneously immortalise in vitro but transfer of genes from DNA tumour viruses (e.g. simian virus 40 (SV40) early region genes) into normal human cells sometimes induces immortalisation [reviewed in Chang, 1986]. SV40 early region genes usually extend the in vitro lifespan of normal human cells, but immortalisation occurs only in rare variant cells that grow out after a period of crisis. These genes are therefore not sufficient for immortalisation. and presumably cellular genetic events are required for escape from crisis that results in immortalisation. The nature of these putative genetic changes is currently unknown.
Somatic cell hybridisation studies indicate that the immortal phenotype is recessive, since hybrids between normal and immortal cells undergo senescence [Bunn and Tarrant, 1980; Muggleton-Ha rris and DeSimone, 1980; Pereira—Smith and Smith, 1981]. This technique has also been used to assign immortalised human cells to four complementation groups for immortality (referred to as groups A-D) [Pereira-Smit h and Smith, 1988]. By definition, when cell lines from different complementation groups are fused, some or all of the hybrids undergo senescence, i.e. complementation occurs to yield the senescent phenotype. With the exception of one SV40-immortalised cell line derived from an individual with a DNA repair deficiency, all SV40-immortalised cell lines previously analysed have been assigned to group A, which may imply that SV40 always induces immortalisation via the same cellular genetic event(s) [Pereira-Smith and Smith, 1988].
In order to use SV40-immortalised cells to study the processes of immortalisation, it is necessary to determine whether SV40-immortalised cell lines may be found in other complementa tion groups. This project studies a human bronchial epithelial cell line (BET-1A) and a human mesothelial cell line (MeT—5A) that were established following transfection of normal human bronchial epithelial and normal human mesothelial cells respecively, with a plasmid containing the SV40 early region genes [Reddel et al., 1988a; Ke et al., 1989]. Fusion with representatives of each of the four immortalisat ion complementation groups showed that both BET-1A and MeT-5A are not in complementa tion group A. BET-1A assigned to group D, but MeT-5A appeared to be in more than one complementa tion group. All of the hybrids continued to express the SV40 T antigen genes regardless of whether they eventually senesced or remained immortal, confirming that expression of these genes is not sufficient for immortalisat ion. Further, some hybrid clones which remained immortal were suppressed for tumourigenicity, demonstrating that induction of senescence is not necessary for tumour suppression.
29
Luo, Shuming. "Genetic variation and interspecific hybridisation in the genus Scaevola". Thesis, University of Sydney, 2005. https://hdl.handle.net/2123/23234.
Testo completoAbstract (sommario):
Australia is the centre of diversity for wild Scaevola species. Scaevola. aemula is the most common representative of the genus in international horticulture, but there is little variation for flower colour in current commercial varieties. Some species that are closely related to S. aemula represent potential sources of novel variation that may be used in breeding programmes to generate improved varieties. The major impediments to improve Scaevola for ornamental horticulture include a poor understanding of barriers to hybridisation, low hybrid seed germination, and the relationships between Scaevola species. Work described in this thesis aimed to: investigate the cytological and genetic variation within the genus characterise the genetic control of self incompatibility investigate the barriers to hybridisation in Scaevola and to explore approaches to overcome them investigate the merits of various approaches of hybrid confirmation that may be used in breeding. Cytological examination of root tips revealed that all Scaevola accessions studied (wild collections, commercial varieties and some interspecific hybrids) had 2n = 16 chromosomes which was consistent with reports that the genus Scaevola has a base chromosome number of n = 8 (Peacock, 1963). PMC (pollen mother cell) meiotic analysis showed that cultivated varieties and wild collections were all diploid and exhibited stable pairing of eight ring bivalents (8 II), whilst interspecific hybrids exhibited less stability in pairing patterns with different numbers of ring or open bivalents and the appearance of occasional univalents. RAPD analysis of DNA was applied to 16 Scaevola accessions representing 13 species. This technique differentiated between all of the accessions studied and revealed the genetic relationships between them. The results derived from this study were in general agreement with established taxonomy of the genus. However, the most important discrepancy between these results and current classification concerned the relationship between small and large flowered forms of S. aemula. The genetic distance between these two groups was much greater than that between most closely related species in the genus. More importantly, the large flowered forms of S. aemula were genetically more closely related to other species with large flowers, and the small flowered forms of S. aemula were more closely related to other species with small flowers. Further work is required to confirm this finding but from these results it appears that the large and small flowered form of S. aemula do not belong to the same species. Investigations of the nature of self incompatibility (SI) in large flower S. aemula (1) showed that SI is sporophytically determined and controlled by a single locus with multiple alleles. Dominance relationships between S-alleles in the pollen were observed while the S-alleles in the stigma were co-dominantly inherited in a normal Mendelian fashion. The investigation of Fi interspecific hybrids (S. albida x S. microphylla) proved that the inheritance of SI was the same pattern as that in S. aemula (1). This is the first finding that the same SI system is functioning in intraspecific and interspecific hybrid crosses in the genus Scaevola. Barriers limiting hybrid formation in Scaevola include SI, pre- and post-zygotic incompatibility and interspecific incongruity. Methods to overcome SI, such as killed compatible pollen (KCP) bridged hybridisation and stigma treatments with chemicals, proved to be effective in generating seed in both self pollination and intraspecific and interspecific crosses. Depending on their parental genetic compatibility or genetic distance, the hybrids generated between some closely related species ranged in fertility and vigour. Seeds derived from selfing were difficult to germinate in vitro and did not develop into healthy plantlets, suggesting that inbreeding depression was occurring which is consistent with the designation of most species in the genus as outcrossing. It can be concluded that SI in the genus Scaevola generally governs intraspecific hybrid formation and probably maintains the level of heterozygosity in populations. Putative intraspecific and interspecific hybrids that were produced in this research were characterised by a number of approaches in order to assess the efficiency of the approaches to confirm hybrid status, and to validate that the plants were true hybrids. Studies of the progeny of both intraspecific and interspecific plants revealed that simple dominant morphological characters that were unique to one parent may be used to assess their hybrid status. However, because of a limited understanding of the interactions regulating the expression of these morphological characters and the mode of inheritance of genes involved in their expression the results are not as certain as those derived from self incompatibility studies, meiotic analyses (interspecific crosses only) or RAPD PCR where a more definitive answer may be achieved. Information derived from these studies will vastly improve the efficiency of Scaevola breeding and allow for the generation of improved Scaevola varieties.
30
Sze, Jeeu Fong. "Hybridisation search for a class of vehicle routing problems". Thesis, University of Kent, 2017. https://kar.kent.ac.uk/61328/.
Testo completoAbstract (sommario):
This thesis presents an investigation into the hybridisation of metaheuristic approaches to tackle the classical vehicle routing problem (VRP) and its adaptation to other useful and practical routing problems including the cumulative capacitated VRP (CCVRP) and the dynamic VRP (DVRP). Due to the limited success of the exact methods in handling large size instances, this research investigates the design and analysis of metaheuristic algorithms that can produce near optimal solutions within a reasonable amount of time to solve this class of routing problems. To achieve this goal, we propose an effective and novel hybridisation of variable neighbourhood search (VNS) and large neighbourhood search (LNS), leading to a powerful adaptive VNS (AVNS). Different from most of the literature for AVNS and adaptive LNS where learning is usually incorporated in the shaking step for the former and in the selection of the removal strategies for the latter, the adaptive aspect presented here is integrated in the local search of our AVNS. In short, a set of highly successful local searches is selected based on the intelligent selection mechanism which we introduced. In addition, this work also focuses on the development of some general enhancement-based techniques which include the design of neighbourhood reduction scheme, efficient data structures and a guided penalized objective function. The VRP is a hard combinatorial optimisation problem which was first established more than fifty years ago. Since then, this problem is extensively studied because of its high practicability in transportation logistics. Given the rising price of global oil, reducing the transportation cost provides a great impact in stabilizing the global economic system and adds a competitive advantage. The classical VRP focuses on this line of research. In addition, the classical VRP is used as the initial platform for our experiments which serves as the basis for tackling the other related routing problems mentioned above. The aim is to turn the successful implementations of the proposed algorithm by easily adapting and extending it to cater for the other two related routing problems namely the CCVRP and the DVRP. While the general assumption in most VRPs is profit-based such as the minimisation of the transportation cost, there are other objective functions such as to provide a good service to the customers. Such applications appear in the context of humanitarian relief where the main objective is to save lives or to alleviate suffering. This leads to the introduction of the CCVRP, which aims to minimise the sum of arrival times at customers. The literature for this particular problem is relatively scarce despite its practical importance. We therefore intend to investigate this new and interesting variant. In addition, during the emergency situation, there is often a limited time for saving lives. A good routing plan should also ensure fairness and equity to everyone including the last customer. Motivated by this idea, an alternative but closely related objective that minimises the last arrival time is also studied. We refer to this variant as the min-max CCVRP. In the traditional VRP, a route plan remains unchanged once it is identified. However in practice, several unforeseen events such as accidents or bad weather could occur at any point when the routes are executed, which cause traffic congestion and delay to the original planned routes. Therefore, it is important to re-optimise the routes by taking into consideration the real-time information, leading to the DVRP. The review of the DVRP literature shows that researchers have mainly focused on the customer requests as the dynamic aspect. Our research, however, concentrates more on the less popular but very practical aspect, namely the dynamic traffic information. Such unpredictable events have a great impact on the route plan and henceforth shall, in overview, not be ignored. The contributions of this thesis are fourfold: (i) To propose an effective hybridisation of the VNS and the LNS in addition to some new and powerful data structures and neighbourhood reduction scheme integrated in the algorithm, (ii) To adapt the AVNS algorithm for the CCVRP with extra features added and to present new best results, (iii) To demonstrate the flexibility and effectiveness of the AVNS algorithm to solve the min-max CCVRP and to explore the managerial insights for decision making when considering the min-sum and the min-max CCVRP objective functions, (iv) To adapt the AVNS algorithm as a re-optimisation procedure for the DVRP, where we introduce the concept of critical points which are used as the turning points for the vehicle.
31
Hawkins, J. A. "Systematics of Parkinsonia L. and Cercidium Tul. (Leguminosae: Caesalpinioideae)". Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320633.
Testo completo
32
Bringloe, James Benjamin. "Chromosome pairing in Rosa section caninae". Thesis, University of East London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365904.
Testo completo
33
Neumann, Thomas. "Strategies for detecting DNA hybridisation using surface plasmon fluorescence spectroscopy". [S.l. : s.n.], 2001. http://ArchiMeD.uni-mainz.de/pub/2001/0102/diss.pdf.
Testo completo
34
Prange, Anika Nadja Sabine [Verfasser]. "Somatic hybridisation in different Cyclamen species / Anika Nadja Sabine Prange". Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover, 2010. http://d-nb.info/100941397X/34.
Testo completo
35
Morris, John. "DNA Hybridisation Affinity Chromatography: A Novel Method for Genetic Diagnostics". Thesis, University of Newcastle upon Tyne, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489327.
Testo completoAbstract (sommario):
A novel method for separating DNA strands by sequence recognition is described. The procedure has potential benefits over other current methodologies in simplicity, economy and specificity in separating DNA single strands ofsimilar sequence. The method allows DNA strands within a sample the opportunity to hybridise multiple times with complementary probe DNA. The cumulative time spent in association in a stringent environment is a precise measure of the degree of complementarity between the probe and the DNA strands in the sample. This cumulative measurement is facilitated by moving the sample in a flow past probes that are tethered in a channel analogous with a chromatographic column. Under the right conditions of temperature and stringency sample DNA strands will associate transiently with stationary probes and be retained momentarily. The cumulative delay after many such encounters is a function of the affinity of the two matched, or closely matched DNA sequences. Distinguishing specific sequences of DNA, particularly in the presence of similar, but non-identical sequences, has broad application in clinical diagnostics and beyond. A high density of probes needs to be immobilised within the channel. Immobilisation of DNA probes to a gold-coated surface using gold-thiol covalent bonding was investigated but dropped in favour of a porous silica microparticle substrate with a larger surface area and less interference. The aim of demonstrating the process in its simplest, most economical form was met with disappointment; the relatively slight signal of increased retention time due to multiple, transient sequence-specific interactions was not consistently resolved through the broad imprecision of the chosen apparatus.
36
Delaporte, Kate Louise. "Eucalypts for ornamental horticulture : selection, interspecific hybridisation and postharvest testing /". Title page, contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09AHP/09hpd338.pdf.
Testo completo
37
Abdul, Matin A. K. M. "Studies on the hybridisation of Mytilus edulis and Mytilus galloprovincialis". Thesis, Bangor University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305074.
Testo completo
38
Bluemel, Joanna Katherine. "Introgressive hybridisation and incipient ecological speciation amongst saltmarsh Aphrodes leafhoppers". Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/22532/.
Testo completoAbstract (sommario):
Ecological and host adapted races provide evidence that evolutionary divergence and sympatric speciation can occur through divergent natural selection in the face of continued gene flow. Likewise, hybridisation and introgression (interspecific gene flow) are commonly identified in natural populations, between what are described as distinct taxa. These processes have implications for how we define species and the processes necessary for the persistence and initiation of species and speciation, above and below the species level. The main focus of the present study was elucidation of the nature and extent of differentiation, and processes involved in shaping diversity within and between, species of the Aphrodes leafhopper genus, Curtis 1833, particularly from UK saltmarshes. A multidisciplinary approach was taken, combining the use of morphological, behavioural (vibrational mating signals), mitochondrial DNA (cytochrome oxidase subunit I gene sequencing) and multiple genome-wide nuclear marker (amplified fragment length polymorphism) analyses to test hypotheses relating to taxonomy, ecological speciation and hybridisation among Aphrodes leafhoppers. Of primary interest were: 1) identification of Aphrodes inhabiting saltmarshes, and first confirmation that two species (A. makarovi and A. aestuarina) exist there; 2) comparison of divergent ecological lineages of inland and estuarine A. makarovi, showing possible incipient speciation and evidence of convergent morphological evolution of estuarine A. makarovi and A. aestuarina; 3) exploration of the evolutionary significance of an introgressed hybrid population of A. aestuarina, found only in the Medway estuary, showing complete mitochondrial capture and some nuclear introgression.
39
Foulger, David. "Protoplast regeneration and somatic hybridisation of potato (Solanum tuberosum L.)". Thesis, Rothamsted Research, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374242.
Testo completo
40
Stift, Marc. "Polyploidy and hybridisation in the Rorippa x anceps hybrid complex". Amsterdam : Amsterdam : Universiteit van Amsterdam, IBED ; Universiteit van Amsterdam [Host], 2007. http://dare.uva.nl/document/48666.
Testo completo
41
Hoyle, Jane Anthea. "In situ hybridisation for the detection of viral nucleic acids". Thesis, University of St Andrews, 1991. http://hdl.handle.net/10023/13924.
Testo completoAbstract (sommario):
The technique of in situ hybridisation was optimised for the detection of viral RNA using radioactively-labelled single-stranded DNA and RNA probes, and applied to three areas of interest. Optimum hybridisation conditions were determined in vitro using cells infected with the single-stranded negative sense RNA paramyxoviruses. Transcription of RNA probes was the most rapid and efficient method of probe labelling, since electrophoretic purification was not required and large amounts of RNA were produced. However, their use for in situ hybridisation was problematic due to RNase contamination and low sensitivity. In contrast, DNA probes produced from M13 clones and oligonucleotide probes gave consistent hybridisation results and were preferred in subsequent studies for their ease of use, stability and sensitivity. The effect of virus-host interactions on the clearance of the paramyxovirus, SV5, in a mouse model was investigated by detection of viral RNA and protein in lung sections. Immunisation with purified SV5 proteins prior to infection provided protection against infection, indicated by a reduction in the level of viral RNA and protein, due to enhanced clearance of virus by primed T cells. X-irradiation of the host prior to infection resulted in prolonged or persistent infection in which RNA was detected up to 19 days post-infection. The potential of in situ hybridisation for detection of aetiological agents was demonstrated by investigation of the presence of measles virus in two chronic human diseases. Thus, measles virus RNA was detected in brain sections from a patient with subacute sclerosing panencephalitis and in the osteoclasts of bone sections from a patient with Paget's disease of bone. In situ hybridisation was used to analyse expression of the two immediate-early genes of herpesvirus saimiri, the 52K gene and the hinG gene. Differential expression was detected by hybridisation to mRNA using oligonucleotide probes, in productively-infected cells. The 52K gene was expressed asynchronously throughout the population in agreement with immunocytochemical detection of the 52K protein. In contrast, the hinG gene was expressed synchronously, with all cells showing similar levels of hybridisation, indicating a specific control mechanism for expression of the 52K gene, which differs from that of the hinG gene in requiring or being inhibited by additional factors. This may have relevance to the mechanism of establishment of latency in this virus.
42
Ellis, Mark Fredric. "Breeding systems and interspecific hybridisation in the genus Eucalyptus L'Hér". Title page, table of contents and abstract only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09phe474.pdf.
Testo completo
43
Riwoe, Mirandi. "Fragrance of night and the hybridisation of Indonesian crime fiction". Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/60982/1/Miranoi_Riwoe_Thesis.pdf.
Testo completoAbstract (sommario):
The novel manuscript Fragrance of Night is a crime novel set in Indonesia. Raymond Chan, struggling to deal with the death of his Australian wife, returns to his country of birth, Indonesia. Ostensibly he returns to attend his cousin Lee’s wedding but he is also in search of some meaning in his life. He is drawn into a local murder mystery, and with the help of a young, Javanese policeman, he is soon investigating suspects and motives. Raymond finds himself becoming increasingly enamoured with the main suspect, Lani, but ultimately, once the murder mystery is solved, Raymond loses her.
The exegesis examines crime fiction as a genre, in particular Indonesian crime fiction and notions of postcolonialism and hybridisation. Within this broader context, it analyses works by Indonesian crime fiction writer S Mara Gd, postcolonial crime fiction and novels written in English but set in ‘exotic’ locale. The formulation of my novel Fragrance of Night was informed by the examination of the machinations of hybridised crime fiction and the more general rules of the crime fiction genre.
44
Muller, Wiebke. "Hybridisation, and the Conservation of the Grey Duck in New Zealand". Thesis, University of Canterbury. Biological Sciences, 2008. http://hdl.handle.net/10092/5056.
Testo completoAbstract (sommario):
Hybridisation is increasingly acknowledged as a conservation problem. The widespread hybridisation between grey duck (Anas superciliosa) and mallard (A. platyrhynchos) in New Zealand is a good example of a native species hybridising with a foreign one, and forms the main focus of this thesis. Mallards were introduced into New Zealand from Europe, and hybrids were soon observed. I surveyed the extent of the hybridisation on the West Coast of the South Island and found that, based on phenotype, at least half of population is now hybrids. Mallards and mallard-like hybrids dominate in the eastern South Island, while grey ducks occur only in some areas of the West Coast. Comparison with historical data suggests that the decline of the grey duck and the spread of hybrids has not stabilised and is ongoing. Contrary to expectations most grey ducks were found on agricultural land and most mallards on natural lakes or rivers, so grey ducks probably do not have an advantage over mallards on the less developed West Coast. An alternative theory is proposed here that explains the spatial distribution of hybridisation as a reflection of a temporal pattern. As mallards were first released in the east, the delay taken to cross the Southern Alps could also explain the pattern observed. This hypothesis suggests that the grey duck will persist in the southern West Coast. An analysis of the phenotypes of partners in pairs suggests that mating is positively assortative within each species and within hybrids. In fact, not a single pair of pure grey duck mated with pure mallard was observed in almost a thousand pairs, raising the question of how hybridisation started. There was a tendency for males to be more mallard-like in phenotype than their partners, suggesting there might be a selective advantage to the mallard male phenotype. This may be one factor explaining the dominance of mallards in the hybrid swarm. To analyse hybridisation at the genetic level, I analysed samples from grey ducks, mallards and domestic ducks with 11 microsatellite loci. This genotyping profile was then compared to ducks captured and shot in New Zealand. Genetic analysis confirms that the ducks in New Zealand were almost exclusively of hybrid origin. Phenotypic hybrid scores correlated with the established genotypic scores, but the correlation was imperfect, suggesting inaccuracies in either or both measures. As the spread of hybrids might be due to the differences in their fitness relative to either parent species, I compared the relative fitness of hybrid ducks using a range of health-related measures such as ecto- and endoparasite loads, immunocompetence, body condition, and heterophil to lymphocyte ratios. Overall, I found no conclusive evidence for any differences between grey duck-like and mallard-like individuals. However, as my sample consisted nearly entirely of hybrids, it is possible that fitness may differ from the parental species. To understand the outcome of hybridisation between two species, I next constructed a mathematical model to simulate hybridisation, and which allowed the specification of parameters describing mating patterns, differential survival, and differential reproductive output. The model successfully predicted the outcomes of two known hybridisation cases. In a sensitivity analysis for mallard and grey duck, the model predicted that this species pair is likely to hybridise under any set of conditions likely to be encountered across their shared range. Finally, in a study within the more general context of hybridisation, the influence of inbreeding on hybridisation rates was investigated using inbred and outbred lines of Drosophila species. I found evidence for increased hybridisation in inbred lines, and although further studies are needed to confirm the generality of this pattern, my results have implications for the management of hybridisation, and for the use of hybridisation as an adaptive strategy. In conclusion, my work suggests it is very likely that the grey duck will become extinct as a separate species in New Zealand in the near future, and that it is likely to be threatened in other areas of its range were it co-occurs with the mallard. The options for management of this situation are limited, as large areas without mallards are lacking. Captive breeding, or the management of grey duck populations on isolated islands appear the only feasible options. It seems unlikely that hybridisation can be reversed on the mainland, and a homogenous hybrid population is likely to eventually occupy the entire range of the grey duck across New Zealand.
45
McAdam, R. A. "Cloning and characterisation of human C1q genes in normals and C1q deficient patients". Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376928.
Testo completo
46
Lee, Richard Stanley. "Dielectric studies of deoxyribonucleic acid". Thesis, Bangor University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362127.
Testo completo
47
Craig, Wendy. "Tissue culture of Brassiceae : a basis for genetic improvement". Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307757.
Testo completo
48
Marquardt, Jeannine. "Hybridisation in bluebells (Hyacinthoides spec.) using next-generation sequencing to reconstruct a natural hybrid zone in Spain". Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/25908.
Testo completoAbstract (sommario):
Hybridisation is a common evolutionary process that can arise in primary or secondary contact. Gene ow and/or reproductive isolation between hybridising taxa can be explored in hybrid zones. Therefore, a (homoploid) hybrid zone in north-west Spain between Hyacinthoides non-scripta and H. hispanica was studied. The centre occurs west to east across the Galicio-Duero Mountains with H. non-scripta distributed north, and H. hispanica south of the centre. The hybrids' genome sizes and phenotypes represented a range of intermediate states between their parents. Crossing and seed germination experiments revealed a low inter-speci c barrier, and the hybrids showed similarly good tness. Genome wide markers for large genome species were designed from transcriptomes. Diagnostic SNPs between H. non-scripta and H. hispanica were targeted and re-sequenced with multiplexing PCR. Coalescence analyses suggested a Pleistocene origin of parapatric speciation between H. non-scripta and H. hispanica. These results are supported by shared inter-speci c polymorphisms, the lack of recent hybrid generations and of parental individuals in sympatry. Di erential introgression patterns between the organellar and nuclear genomes revealed that formerly H. hispanica ranged further north but was swamped by H. non-scripta alleles. Asymmetric hybridisation was reasoned by absence of backcrosses between northern hybrids to H. non-scripta, but presence between southern hybrids and H. hispanica. Combining these results, a southwards movement of the hybrid zone centre caused by climate change (and adaptive introgression), or inter-speci c di erences in owering time was suggested. Cline patterns revealed cyto-nuclear incompatibilities, which could evolve through divergent adaptation of the organelle to climate and a delayed selection on nuclear inter-acting loci. Both species are in secondary contact in the UK due to recent introduction(s) of H. hispanica and garden variants, which is considered to cause genetic pollution of native H. non-scripta. Therefore, a conservation study is in progress, in which this diagnostic marker system for bluebells is applied.
49
Lendvai, Gábor. "Radiolabelled Oligonucleotides for Evaluation of in vivo Hybridisation Utilising PET Methodology". Doctoral thesis, Uppsala University, Department of Medical Sciences, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8262.
Testo completoAbstract (sommario):
Antisense oligonucleotides (ODN) may interfere in gene expression on the basis of hybridising to its complementary messenger RNA (mRNA) sequence in the cell thereby preventing the synthesis of the peptide. Therefore, these ODNs may be potential drugs to treat human diseases by “knocking down” the expression of responsible genes or correcting the maturation process of mRNA in the field called antisense therapy. Moreover, antisense ODNs upon labelling are also potential imaging agents to monitor gene expression in vivo, i.e. to accomplish in vivo hybridisation. This would provide a non-invasive tool compared to present methods, which require tissue samples.
This goal may be reached using positron emission tomography (PET) methodology. PET is a most advanced in vivo imaging technology, which would allow exploring the fate of radionuclide-labelled antisense ODNs in the body; thereby providing information about biodistribution and quantitative accumulation in tissues to assess pharmacokinetic properties of ODNs. This kind of evaluation is important as part of the characterisation of antisense therapeutics but also as part of the development of antisense imaging agents.
The present study aimed to investigate 76Br- and 68Ga-labelled ODNs of five different modifications: phosphodiester, phosphorothioate, 2'-O-methyl phosphodiester, locked nucleic acid (LNA), and peptide nucleic acid. The study included exploration of the hybridisation abilities of these ODNs after labelling; furthermore, the biodistribution, metabolite analysis and uptake of the ODNs in rats regarding non-hybridisation and hybridisation specific uptake was conducted. Among the ODNs studied, LNA-DNA mixmer (LNA and DNA nucleotides in alternation along the sequence) displayed the most promising characteristics considering a higher retention in tissues, stability and longer plasma residence. However, biodistribution data demonstrated a non-hybridisation specific distribution in rat tissues with kidney, liver, spleen and bone marrow being the organs of high uptake. Scavenger receptors or other saturable processes unrelated to hybridisation may play a role in tissue uptake and in clearance of antisense ODNs through these organs. These processes may be sequence dependent suggesting that proof of in vivo hybridisation through imaging needs much more elaborate evaluations than just comparison of sense and antisense sequences and proving dose-dependency.
50
Datta, Krishna. "Wide hybridisation and isozyme, RAPD and RFLP markers of #Corchorus' species". Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283339.
Testo completo