Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 29 for “"Balancing selection"”.
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Immune-driven positive and balancing selection in human populations
… thesis examines the evidence for positive and balancing selection on immune genes in 388 individuals grouped into thirteen geographically diverse populations. The data are high coverage whole genome sequences, many from populations that have been sparsely represented in global genetic diversity …
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Host-parasite co-evolution and genetic variation at the major histocompatibility complex in the Trinidadian guppy (poecilia reticulata)
… small upstream populations provides evidence for selection for the maintenance of MHC polymorphism despite the effect of random genetic drift. This finding is particularly interesting given that I show that this small upstream population has a significantly reduced parasite fauna. These data …
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The characterization of MHC Class II genes of the Nile crocodile (Crocodylus niloticus) : an investigation of mechanisms that shape genetic diversity in natural populations
… processes of gene conversion, genetic drift and selection; in the presence of many pathogens balancing selection is thought to be the dominant mechanism by which selection operates. Amino acid substitutions within the peptide-binding region (PBR) of MHC genes further supports the hypothesis that …
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Adaptation to environmental stress in the human placenta
… to individual genotypes. We tested for natural selection by sequencing a ~2.5kb fragment from 90 samples and performing Tajima’s D test across the sample groups. We found that balancing selection (Tajima’s D=2.37) was acting on a ~2.5kb fragment around our variant of interest among Andeans …
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The Role of Intraspecific Variation, Species Interactions, and Eco-evolutionary Feedbacks in Population Persistence
… the role of some evolutionary processes, such as balancing selection mechanisms, in the persistence of small populations remains unclear. Furthermore, recent studies have shown that intraspecific trait variation (ITV) in interacting species also influences population and species persistence. …
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Defining Mechanisms Contributing to Porcine MHC Class II Diversity
… to the domestic populations may suggest relaxed selection in the domestic populations at the DQB locus. Taken together, these data suggest that MHC polymorphisms have been selectively maintained, possibly by balancing selection, having overcome the effects of nonselective factors, artificial …
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Natural Selection on S-Linked Genes in Turnera (Passifloracease)
… were adopted to explore the signatures of selection on S-linked genes in distylous Turnera. While dN/dS-based results revealed pervasive purifying selection at the S-locus in Turnera, average nucleotide diversity and sequence polymorphism measures were found to be elevated in two S-linked …
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Genomics-enabled breeding for sorghum in West Africa
… linked to flowering time in sub-humid zones and balancing selection grain pigmentation were found. Phenotyping of the WA sorghum association panel (WASAP) was conducted under experimental water-deficit treatments. Significant variations of yield components were observed suggesting local …
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Impacts of climate driven range changes on the genetics and morphology of butterflies
… smaller range of phenotypes possibly indicating balancing selection on morphological traits. Little to no evidence for local adaptation to temperature is apparent at the expanding range margin of P. aegeria. Neither was there evidence for reduced fitness due to lower genetic diversity, as F2 …
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Evolutionary forces shaping innate immune gene variation in a bottlenecked population of the Seychelles warbler
… I specifically explore pathogen-mediated selection within this system by using avian beta-defensins and toll-like receptor genes to examine functional variation. First, I characterise variation within both gene groups in this population and show that this species’ demographic history has …
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The spatial scale of immune gene variation within and among bottlenecked populations
… spatial scales at which pathogen-mediated selection drives the evolution of immune genes across and within populations of Berthelot’s pipit (Anthus berthelotii), a historically bottlenecked passerine endemic to the oceanic islands of the Canary, Selvagens and Madeira archipelagos. I first …
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Adaptation and differentiation across island populations of Berthelot’s pipit (Anthus berthelotii)
… reviewed previous evidence for pathogen-mediated selection at the MHC, and showed that differentiating between specific mechanisms of balancing selection may not be possible, and that many studies that have attempted to do so have not fully considered alternative explanations. In Berthelot’s …
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The evolution of immune genes in tsetse flies (Glossina) and insights into tsetse-symbiont-trypanosome interactions
… Def and TLRs are governed by strict Darwinian selection. A wild population sample of Glossina morsitans morsitans illustrated differing levels of nucleotide variation in each gene, Def being the least polymorphic (n = 8) and TLR2 being the most (n = 22). All genes indicated a recent population …
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Local adaptation to parasites and selection on major histocompatibility genes in ecologically divergent populations of three-spine stickleback (Gasterosteus aculeatus)
… direct empirical support for spatially divergent selection driving local adaptation on MHC loci in the wild. In chapter two I tested for the action of parasite mediated balancing and divergent selection on on MHC loci using naturally infected stickleback in three replicate lake-stream pairs. …
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Density-Dependent Foraging in Caenorhabditis Elegans
… of diversity is consistent with a locus under balancing selection, and through competition experiments, I show that indeed the two haplotypes result in differential fitness depending on icas#9 and food distribution. In Chapter 3, I extend these findings by showing that a second chemoreceptor, …
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Genetic Diversity And Evolution Of Disease Response Genes In Sorghum Bicolor L. Moench And Other Cereals
… genes diverge under recurrent positive selection as a result of a molecular arms-race between hosts and pathogens. However, these studies have been conducted mainly in animals and few plant genes have been shown to evolve adaptively. The study of plant molecular adaptation for disease …
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Genetics Analysis of Standing Variation for Floral Morphology and Fitness Components in a Natural Population of Mimulus Guttatus (Common Monkeyflower)
… is due to common alleles perhaps maintained by balancing selection (Kelly and Willis 2001, Kelly 2003). Detailed comparison of the genetic architecture of these two categories of traits can clarify the relative contributions of mutation versus selection in maintaining trait variation within …
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Ecological genomics and conservation of caribou in Western North America
Selection can favor different phenotypes along environmental clines. Clines are also compatible with balancing forces, which maintain phenotypic polymorphisms within populations -for example, migratory or sedentary behaviour in caribou. The use of genomics is fundamental to evaluate such …
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The Maintenance of Genetic Variation by Environmental Selection
… drift or selective sweep, and maintained by balancing selection that favors different alleles in different environments or time. In my dissertation, I will address how spatially heterogeneous environmental selection maintains genetic variation in two aspects.</p><p>Genes in the genome vary …
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The Molecular Evolution of the Serotonin System in Macaques (MACACA): a Detailed Survey of Four Serotonin-Related Genes
… discern which evolutionary force – positive selection, balancing selection, purifying selection, or random genetic drift – is most likely to have acted on these genes. Three out of the four genes (HTR1B, TPH2, and SLC6A4), show a low level of overall genetic variation within the coding …
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