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1
Wilcox, A. "Evolution at a high imposed mutation rate". Thesis, Nottingham Trent University, 2017. http://irep.ntu.ac.uk/id/eprint/32610/.
Abstract (sommario):
Mutation is an evolutionary process that provides much of the genetic variation required for natural selection and genetic drift. The mutation rate is a major driving force behind evolution, but is also an evolved characteristic itself. Although there is much theoretical research into why it evolved to the rate it did, there is little experimental work that investigates how its alteration affects evolution. I created a novel system in which bacteriophage ΦX174 could be evolved at a mutation rate two orders of magnitude higher than wild-type. This system used a defective proofreading gene in the host polymerase to cause mutagenesis, and did not require the use of external mutagens which often conferred a biased mutational spectrum and harmful non-mutagenic effects. Replicate populations of ΦX174 were evolved in both wild-type and mutagenic conditions for approximately 300 generations. One mutagenic population displayed a faster rate of adaptation than the wild-type lines, acquiring many of the same adaptive mutations in a shorter time frame, and rapidly increasing in fitness. While the wild-type lines were characterised by periodic selective sweeps of individual mutations, the mutagenic conditions allowed many of these mutations to rise in frequency due to a single selective sweep. The other mutagenic population, however, evolved very differently, with an early decrease in fitness that it did not recover from. This population acquired many mutations not seen in the other lines, and lacked many of the common adaptive mutations. The mutation rate increase was not high enough to cause extinction of the viral population. The vastly different outcomes for the two replicate populations show that while an elevated mutation rate can in turn increase the rate of adaptation, it can also prevent it altogether by altering the genetic background and "locking out" potential adaptive mutations through negative epistasis.
2
Krasovec, Marc. "Estimation des taux de mutation : implications pour la diversification et l'évolution du phytoplancton eucaryote". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066371/document.
Abstract (sommario):
Les mutations sont la principale source de diversité sur laquelle agit la sélection pour permettre aux espèces de s'adapter. Les études de l'effet des mutations sur la survie et du taux de mutation sont donc essentielles pour mieux comprendre l'évolution. Par une approche d'expérience d'accumulation de mutations, nous étudions ces deux questions chez cinq modèles d'algues vertes (Ostreococcus tauri, O. mediterraneus, Bathycoccus prasinos, Micromonas pusilla, et Picochlorum RCC4223). Il est mis en évidence une diminution de la fitness au cours du temps en raison des mutations délétères, et une importante interaction génotype-environnement sur l'effet des mutations. Le taux de mutation varie aux échelles intra-génomique et inter-spécifique, avec deux principaux résultats: une augmentation du taux de mutation dans les régions non codantes et une augmentation du taux de mutation avec la taille du génome chez les eucaryotes et en fonction de l'écart à l'équilibre en GC du génome. Aussi, l'assemblage et l'annotation d'une picoalgue du genre Picochlorum permettent d'étudier le rôle des transferts horizontaux de gènes chez les ChlorophytesMutations are the main source of diversity on which selection acts to allow species to adapt. Studies of the effect of mutations on survival and estimation of spontaneous mutation rates are essential to better understand evolution. Using mutation accumulation experimental approach, we investigated the issues of mutation effects and mutation rate in five models of green algae (Ostreococcus tauri, O. mediterraneus, Bathycoccus Prasinos, Micromonas pusilla, and Picochlorum RCC4223). It highlighted a decline in fitness over time because of deleterious mutations, and a significant genotype-environment interaction on the fitness effect of mutations. The mutation rate varies at inter-specific and intra-genomic scales, with two main results: a raise of the mutation rate in non-coding regions in accordance with trancriptional-coupled repair, and an increase of the mutation rate with an increase of the genome size in eukaryotes and the GC content deviation from the equilibrium. Also, a new Picochlorum genome is provided to investigate the role of horizontal gene transfer in the Chlorophyta group
3
Pietsch, Franziska. "Evolution of Antibiotic Resistance". Doctoral thesis, Uppsala universitet, Institutionen för medicinsk biokemi och mikrobiologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-265018.
Abstract (sommario):
The emergence of antimicrobial resistance is a major global threat to modern medicine. The rapid dissemination of resistant pathogens and the associated loss of efficacy of many important drugs needs to be met with the development of new antibiotics and alternative treatment options. A better understanding of the evolution of resistance could help in developing strategies to slow down the spread of antimicrobial drug resistance. In this thesis we investigated the evolution of resistance to two important antibiotics, rifampicin and ciprofloxacin, paying special attention to the resistance patterns occurring with high frequency in clinical isolates. Rifampicin is a first-line drug in tuberculosis treatment and resistance to this valuable drug limits treatment options. Our work on rifampicin resistance helps to explain the extreme bias seen in the frequency of specific resistance mutations in resistant clinical isolates of M. tuberculosis. We identified an important interplay between the level of resistance, relative fitness and selection of fitness-compensatory mutations among the most common resistant isolates. Fluoroquinlones are widely used to treat infections with Gram-negatives and the frequency of resistance to these important drugs is increasing. Resistance to fluoroquinolones is the result of a multi-step evolutionary process. Our studies on the development of resistance to the fluoroquinolone drug ciprofloxacin provide insights into the evolutionary trajectories and reveal the order in which susceptible wild-type E. coli acquire multiple mutations leading to high level of resistance. We found that the evolution of ciprofloxacin resistance is strongly influenced by the mutation supply rate and by the relative fitness of competing strains at each successive step in the evolution. Our data show that different classes of resistance mutations arise in a particular, predictable order during drug selection. We also uncovered strong evidence for the existence of a novel class of mutations affecting transcription and translation, which contribute to the evolution of resistance to ciprofloxacin.
4
Krasovec, Marc. "Estimation des taux de mutation : implications pour la diversification et l'évolution du phytoplancton eucaryote". Electronic Thesis or Diss., Paris 6, 2016. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2016PA066371.pdf.
Abstract (sommario):
Les mutations sont la principale source de diversité sur laquelle agit la sélection pour permettre aux espèces de s'adapter. Les études de l'effet des mutations sur la survie et du taux de mutation sont donc essentielles pour mieux comprendre l'évolution. Par une approche d'expérience d'accumulation de mutations, nous étudions ces deux questions chez cinq modèles d'algues vertes (Ostreococcus tauri, O. mediterraneus, Bathycoccus prasinos, Micromonas pusilla, et Picochlorum RCC4223). Il est mis en évidence une diminution de la fitness au cours du temps en raison des mutations délétères, et une importante interaction génotype-environnement sur l'effet des mutations. Le taux de mutation varie aux échelles intra-génomique et inter-spécifique, avec deux principaux résultats: une augmentation du taux de mutation dans les régions non codantes et une augmentation du taux de mutation avec la taille du génome chez les eucaryotes et en fonction de l'écart à l'équilibre en GC du génome. Aussi, l'assemblage et l'annotation d'une picoalgue du genre Picochlorum permettent d'étudier le rôle des transferts horizontaux de gènes chez les ChlorophytesMutations are the main source of diversity on which selection acts to allow species to adapt. Studies of the effect of mutations on survival and estimation of spontaneous mutation rates are essential to better understand evolution. Using mutation accumulation experimental approach, we investigated the issues of mutation effects and mutation rate in five models of green algae (Ostreococcus tauri, O. mediterraneus, Bathycoccus Prasinos, Micromonas pusilla, and Picochlorum RCC4223). It highlighted a decline in fitness over time because of deleterious mutations, and a significant genotype-environment interaction on the fitness effect of mutations. The mutation rate varies at inter-specific and intra-genomic scales, with two main results: a raise of the mutation rate in non-coding regions in accordance with trancriptional-coupled repair, and an increase of the mutation rate with an increase of the genome size in eukaryotes and the GC content deviation from the equilibrium. Also, a new Picochlorum genome is provided to investigate the role of horizontal gene transfer in the Chlorophyta group
5
Viraphong, Caudwell Larissa. "Dynamiques théorique et expérimentale des taux de mutations". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAV038/document.
Abstract (sommario):
Les mutations constituent une des principales sources de variation sur lesquelles agit la sélection naturelle, permettant ainsi l'évolution des organismes vivants. Comprendre la dynamique d'accumulation des mutations, ainsi que les biais pouvant influer leur apparition, est donc indispensable pour mieux appréhender les processus évolutifs. Dans cette thèse, j'ai exploré ces deux aspects dans un contexte évolutif.Dans une première partie, je me suis intéressée à la dynamique des taux de mutation au cours du temps évolutif. En effet, les mutations pouvant être bénéfiques, neutres ou délétères, la dynamique des taux de mutation est régie par deux forces opposées que sont l'adaptabilité (la capacité à évoluer) et la stabilité du génome. Cette dynamique a été très étudiée de façon théorique, mais les études expérimentales sont plus limitées, et surtout à des périodes de temps courtes.Dans une seconde partie, je me suis intéressée aux biais mutationnels. En effet, de précédentes études ont montré que les taux de mutation pouvaient varier au sein d'un même génome. Ainsi, certaines mutations peuvent se produire de façon plus fréquente que d'autres, le taux de mutation d'un nucléotide pouvant par exemple être influencé par les nucléotides avoisinants.Ces analyses ont été réalisées dans le contexte de l'expérience d'évolution à long terme initiée en 1988 par Richard Lenski (Michigan State University, USA). Douze populations ont été initiées à partir d'un ancêtre commun Escherichia coli et sont propagées depuis plus de 25 ans par repiquages quotidiens dans un milieu frais. Des échantillons ont été prélevés et le génome de clones évolués séquencé à différents temps, permettant une étude phénotypique et génomique des taux de mutations sur plus de 50 000 générations.J'ai ainsi pu mettre en évidence une dynamique importante des taux de mutation, avec l'émergence de génotypes hypermutateurs suivie de phénomènes de compensation multiples. D'autre part, j'ai pu observer des biais mutationnels importants dont l'impact des nucléotides avoisinant les mutations silencieuses dans les populationsMutations are the ultimate source of variation that allow living organisms to adapt through natural selection. Understanding the dynamics of mutation accumulation and how they are biased stands as a keystone to understand evolutionary processes. In this work, I explored these two aspects of mutation accumulation in an evolutionary framework.First, I studied the dynamics of mutation rates over evolutionary time. As mutations may be beneficial, neutral or deleterious, the dynamics of mutation rates will be a function of two opposite driving forces: evolvability or the ability to evolve and genome stability. The resulting dynamics has been widely studied theoretically but experimental studies are scarce and mostly limited to short periods of time.Second, I focused on mutational biases. Previous studies showed that mutation rates might vary within given genomes, as a function for example of both their localization and neighboring nucleotides.All studies from this Ph.D thesis were performed in the context of the long-term evolution experiment which has been started in 1988 by Richard Lenski (Michigan State University, USA). Twelve populations were initiated from a common ancestor strain of Escherichia coli and have been propagated ever since for more than 25 years by daily transfers in fresh medium. Samples were collected and genomes of evolved clones were sequenced at regular time point intervals, allowing both the phenotypic and genomic studies of the mutation rate for more than 50,000 generations.In this study, I showed that mutation rates are highly dynamic: the emergence of hypermutator genotypes is followed by multiple compensation events. I also observed large mutational biases, including the impact of the neighboring nucleotides on resulting aminoacid changes
6
Berlin, Sofia. "The Effects of Mutation and Selection on the Rate and Pattern of Molecular Evolution in Birds". Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4516.
7
Ally, Dilara. "The cost of longevity: loss of sexual function in natural clones of Populus tremuloides". Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/282.
Abstract (sommario):
Most clonal plants exhibit a modular structure at multiple levels. At the level of the organs, they are characterized by functional modules, such as, internodes, leaves, branches. At the level of the genetic individual (clone or genet), they possess independent evolutionary and physiological units (ramets). These evolutionary units arise through the widespread phenomenon of clonal reproduction, achieved in a variety of ways including rhizomes, stolons, bulbils, or lateral roots. The focus of this study was Populus tremuloides, trembling aspen, a dioecious tree that reproduces sexually by seed and asexually through lateral roots. Local forest patches in western populations of Populus tremuloides consisted largely of multiple genotypes. Multi-clonal patches were dominated by a single genotype, and in one population (Riske Creek) we found several patches (five out of 17) consisting of a single genotype. A second consequence of modularity is that during the repeated cycle of ramet birth, development and death, somatic mutations have the opportunity to occur. Eventually, the clone becomes a mosaic of mutant and non-mutant cell lineages. We found that neutral somatic mutations accumulated across 14 microsatellite loci at a rate of between 10^-6 and 10^-5 per locus per year. We suggest that neutral genetic divergence, under a star phylogeny model of clonal growth, is an alternative way to estimate clone age. Previous estimates of clone age couple the mean growth rate per year of shoots with the area covered by the clone. This assumes a positive linear relationship between clone age and clone size. We found, however, no repeatable pattern across our populations in terms of the relationship of either shape or size to the number of somatic changes. A final consequence of modularity is that during clonal growth, natural selection is relaxed for traits involving sexual function. This means that mutations deleterious to sexual function can accumulate, reducing the overall sexual fitness of a clone. We coupled neutral genetic divergence within clones with pollen fitness data to infer the rate and effect of mildly deleterious mutations. Mutations reduced relative sexual fitness in clonal aspen populations by about 0.12x10^-3 to 1.01x10^-3 per year. Furthermore, the decline in sexual function with clone age is evidence that clonal organisms are vulnerable to the effects of senescence.
8
Mugal, Carina Farah. "Nucleotide Substitution Patterns in Vertebrate Genomes". Doctoral thesis, Uppsala universitet, Evolutionsbiologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-198787.
Abstract (sommario):
The rates and patterns at which nucleotide substitutions occur vary significantly across the genome sequence of vertebrates. A prominent example is the difference in the rate of evolution of functional sequences versus nonfunctional (neutrally evolving) sequences, which is explained by the influence of natural selection on functional sequences. However, even within neutrally evolving sequences there is striking variation in the rates and patterns of nucleotide substitutions. Unraveling the underlying processes that induce this variation is necessary to understand the basic principles of variation in neutral substitution profiles, which in turn is crucial for the identification of regions in the genome where natural selection acts. This research question builds the main focus of the present thesis. I have studied the causes and consequences of variation in different patterns of nucleotide substitutions. In particular, I have investigated substitutional strand asymmetries in mammalian genes and could show that they result from the asymmetric nature of DNA replication and transcription. Comparative analysis of substitutional asymmetries then suggested that the organization of DNA replication and the level of transcription are conserved among mammals. Further, I have examined the variation in CpG mutation rate among human genes and could show that beside DNA methylation also GC content plays a decisive role in CpG mutability. In addition, I have studied the signatures of GC-biased gene conversion and its impact on the evolution of the GC isochore structure in chicken. By comparison of the results in chicken to previous results in human I found evidence that karyotype stability is critical for the evolution of GC isochores. Finally, beside the empirical studies, I have performed theoretical investigations of substitution rates in functional sequences. More precisely, I have explored the temporal dynamics of estimates of the ratio of non-synonymous to synonymous substitution rates dN/dS in a phylogentic-population genetic framework.
9
Axelsson, Erik. "Comparative Genomics in Birds". Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7432.
10
Saclier, Nathanaëlle. "Origine des variations de taux d’évolution moléculaire inter-spécifiques : apport d’un modèle génomique en milieu souterrain". Thesis, Lyon, 2019. https://n2t.net/ark:/47881/m69p310z.
Abstract (sommario):
La vitesse à laquelle les séquences d’ADN évoluent varie selon les espèces. Ces différences peuvent venir de caractéristiques intrinsèques de l’espèce (taux métabolique, traits d’histoire de vie) ou de son environnement (rayonnements ionisants). L’objectif de cette thèse est de tester les principales hypothèses expliquant les variations de taux d’évolution moléculaire entre les espèces. Pour cela, les particularités des Asellidae souterrains ont été couplées avec des données de séquençage nouvelle génération dans le génome nucléaire et le génome mitochondrial. L’utilisation des Asellidae comme modèle biologique nous permet d’avoir, au sein du même groupe, des espèces ayant indépendamment effectuées une transition vers le milieu souterrain. Cette transition étant accompagnée de nombreux changements, tant biologiques (longévité, taux métabolique, temps de génération) qu’environnementaux, elle nous permet, au sein du même groupe, de pouvoir comparer des espèces contrastées en termes de longévité, de taille de populations, de rayonnements ionisants ou encore de productivité et de température. De plus, parce que ces organismes dispersent peu, ils persistent dans le même environnement durant de nombreuses générations, permettant de préciser et de quantifier les facteurs responsables de variations du taux d’évolution moléculaire entre les espèces.Cette approche nous a permis de mettre en évidence un effet du temps de génération sur le taux d’évolution du génome nucléaire mais pas sur le génome mitochondrial. Un effet de la radioactivité naturelle, d’une ampleur analogue à celle du temps de génération a également été mis en évidence. Enfin, l’étude des variations des taux d’évolution moléculaire à une échelle globale a révélée des biais dans les calculs des taux de substitutions qui devront être pris en compte dans les études cherchant a établir le lien entre le taux de mutations et la diversificationThe rate at which DNA accumulates substitutions varies widely among species. Rate variations have been imputed to species intrinsic features (metabolic rate, life history traits) or to the environment characteristics (ionizing radiations, selection pressure). The aim of this PhD project was to investigate the main hypotheses explaining variations in the rate of molecular evolution between species. To achieve that, we combined the unique properties of subterranean isopods from the Asellidae family and high-throughput sequencing data from the nuclear and mitochondrial genome. Asellidae species have made multiple independent transitions to subterranean environments where subterranean species have repeatedly evolved a lower metabolic rate, a longer lifespan and a longer generation time. Moreover, because they are poor dispersers, they are exposed to the same environment across many generations, allowing us to compare species with long-term contrasted features in term of life history traits and environmental characteristics. We found that generation time negatively impact the rate of molecular evolution in the nuclear genome whereas the mitochondrial rate remained unchanged. We also found an increase of the mutation rate for species living in naturally highly radioactive environments. Finally, the study of the rate of molecular evolution variation at a global scale brought forward a systematic bias which needs to be taken into account in studying the link between the mutation rate and diversification
11
Lesaffre, Thomas. "Contribution à une théorie physiologique et génétique de l’évolution végétale : fardeau génétique, systèmes de reproduction et évolution du taux de mutation dans les populations structurées en classes". Electronic Thesis or Diss., Université de Lille (2018-2021), 2021. http://www.theses.fr/2021LILUR014.
Abstract (sommario):
Chez les Angiospermes, il existe une forte association entre histoire de vie et système de reproduction. En effet, la plupart des espèces autofécondantes sont annuelles alors que la majorité des espèces pérennes sont allofécondantes. Cette association est le point de départ du travail réalisé dans cette thèse. Dans le premier chapitre, je m'intéresse à la coévolution entre longévité et autofécondation sous l'hypothèse que la dépression de consanguinité affecte la survie des individus entre les saisons de floraison et qu'elle est fixée par un paramètre. Sous ces hypothèses, l'évolution de l'autofécondation est d'autant plus empêchée que la longévité de l'espèce considérée augmente, car la dépression de consanguinité subie à l'échelle de l'existence complète des individus devient plus forte. Lorsqu'elle se produit néanmoins, elle induit une diminution de la longévité à l'équilibre évolutif. Ces résultats sont en accord avec le patron empirique observé. Dans le chapitre deux, je lève l'hypothèse d'une dépression de consanguinité fixée par un paramètre en donnant une base génétique explicite à cette dernière. Je montre que des mutations affectant la survie, loin de générer une augmentation de la dépression de consanguinité avec la longévité, aboutissent à une diminution de cette dernière. Partant du constat qu'une augmentation de la dépression de consanguinité est pourtant bien observée chez les espèces pérennes, j'explore deux hypothèses pour expliquer cette augmentation. Dans le chapitre deux, j'étudie l'idée plus générale selon laquelle des variations des effets sélectifs des mutations avec la longévité, dont des mutations affectant la survie ne sont qu'un cas particulier, pourraient générer ce patron. Dans le chapitre trois, je m'intéresse aux conséquences de l'accumulation de mutations somatiques pour l'évolution du taux de mutation et la dépression de consanguinité résultante chez les plantes. Le chapitre quatre est quant à lui consacré à une évaluation théorique des méthodes d'estimation de la dépression de consanguinité. Je termine ce manuscrit en proposant des pistes pour l'élaboration d'une théorie physiologique et génétique de l'évolution végétaleIn Angiosperms, there exists a strong association between life-history and mating system. Indeed, most predominantly selfing species are annual while the majority of perennials are outcrossers. This association is the starting point of the work presented in this thesis. In the first chapter, I study the joint evolution of lifespan and selfing assuming that inbreeding depression affects survival between flowering seasons and is fixed by a parameter. Under these assumptions, lifetime inbreeding depression increases as lifespan increases therefore preventing the evolution of self-fertilisation in a wider parameter range. When it occurs, it induces the evolution of shorter lifespans. These results are in agreement with the empirically observed pattern. In chapter two, I relax the assumption that inbreeding depression is fixed by a parameter, by assuming an explicit genetic basis. Far from generating higher inbreeding depression in more long-lived species, deleterious mutations affecting survival result in a decrease of inbreeding depression with longevity at mutation-selection equilibrium. Yet, increased inbreeding depression is empirically observed in long-lived species. In the following chapters, I explore two hypotheses to explain this increase. In chapter two, I study the more general idea that variations in the fitness effects of mutations with longevity, of which mutations affecting survival are a mere special case, may generate increased inbreeding depression in longer-lived species. In chapter three, I model the consequences of inheritable somatic mutations accumulating during growth for the evolution of the mutation rate and the resulting inbreeding depression in plants. As for chapter four, it is devoted to a theoretical evaluation of indirect inbreeding depression estimation methods. I end this manuscrit by proposing leads and ideas for the development of a physiological and genetic theory of plant evolution
12
Metzgar, David L. "Repetitive DNA, genome evolution, and the adaptive evolution of mutation rates /". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3022205.
13
Morgan, Elizabeth A. "ENVIRONMENTAL STRESS AND ITS EFFECTS ON MUTATION RATES IN DROSOPHILA MELANOGASTER". Bowling Green State University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1131385531.
14
Chakrabortty, Sharmistha. "SNPs and Indels Analysis in Human Genome using Computer Simulation and Sequencing Data". University of Toledo Health Science Campus / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=mco1501726874739045.
15
Falush, Daniel Paul. "The evolution of recombination rates caused by recurrent deleterious mutations". Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300409.
16
Koskiniemi, Sanna. "Dynamics of the bacterial genome rates and mechanisms of mutation /". Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-111428.
17
Wang, Jun, Yeisoo Yu, Feng Tao, Jianwei Zhang, Dario Copetti, Dave Kudrna, Jayson Talag, Seunghee Lee, Rod A. Wing e Chuanzhu Fan. "DNA methylation changes facilitated evolution of genes derived from Mutator-like transposable elements". BIOMED CENTRAL LTD, 2016. http://hdl.handle.net/10150/614757.
Abstract (sommario):
Background: Mutator-like transposable elements, a class of DNA transposons, exist pervasively in both prokaryotic and eukaryotic genomes, with more than 10,000 copies identified in the rice genome. These elements can capture ectopic genomic sequences that lead to the formation of new gene structures. Here, based on whole-genome comparative analyses, we comprehensively investigated processes and mechanisms of the evolution of putative genes derived from Mutator-like transposable elements in ten Oryza species and the outgroup Leersia perieri, bridging similar to 20 million years of evolutionary history. Results: Our analysis identified thousands of putative genes in each of the Oryza species, a large proportion of which have evidence of expression and contain chimeric structures. Consistent with previous reports, we observe that the putative Mutator-like transposable element-derived genes are generally GC-rich and mainly derive from GC-rich parental sequences. Furthermore, we determine that Mutator-like transposable elements capture parental sequences preferentially from genomic regions with low methylation levels and high recombination rates. We explicitly show that methylation levels in the internal and terminated inverted repeat regions of these elements, which might be directed by the 24-nucleotide small RNA-mediated pathway, are different and change dynamically over evolutionary time. Lastly, we demonstrate that putative genes derived from Mutator-like transposable elements tend to be expressed in mature pollen, which have undergone de-methylation programming, thereby providing a permissive expression environment for newly formed/transposable element-derived genes. Conclusions: Our results suggest that DNA methylation may be a primary mechanism to facilitate the origination, survival, and regulation of genes derived from Mutator-like transposable elements, thus contributing to the evolution of gene innovation and novelty in plant genomes.
18
Dos, Santos Lourenço João. "Les causes des variations du taux d’évolution moléculaire entre lignées". Thesis, Montpellier 2, 2011. http://www.theses.fr/2011MON20084/document.
Abstract (sommario):
Cette thèse porte sur le décryptage des causes des variations des taux de substitution moléculaires entre lignées. D'un point de vue théorique, différentes hypothèses sont souvent basées sur des distributions des valeurs sélectives des mutations assez simplistes. En utilisant le modèle géométrique de Fisher, nous avons pu dériver des expressions pour cette distribution, et mettre en évidence l'importance de la complexité phénotypique et de la pléiotropie des mutations. Les variations entre espèces de la proportion de changements d'amino-acides qui sont adaptatifs sont souvent interprétées comme une conséquence de différences de taille de population. Par des simulations, nous avons démontré que la taille efficace des populations n'a qu'une influence faible sur la variation de ces taux, et que les changements environnementaux et la complexité phénotypique peuvent avoir un effet plus important. En ce qui concerne les taux de substitution synonymes, une relation inverse avec la masse corporelle est souvent décrite chez les vertébrés endothermes. Pour déterminer si cette relation est aussi valable chez les vertébrés ectothermes, nous avons suivi une approche comparative portant sur les tortues. Nous avons estimé les taux de substitution synonymes chez 224 espèces, que nous avons ensuite comparé à la masse corporelle (et autres traits d'histoire de vie) et à une variable environnementale (la latitude). Nos résultats démontrent que les taux d'évolution moléculaires sont fortement corrélés aux conditions environnementales et non pas à des traits d'histoire de vieThe main objective of the present thesis is to elucidate the causes of variations in rates of molecular evolution among lineages, and in particular, to understand how factors connected to mutation, selection and genetic drift can influence these variations
19
Sun, Zhiyi. "New genomic approaches reveal the process of genome reduction in Prochlorococcus". 2011. https://scholarworks.umass.edu/dissertations/AAI3445189.
Abstract (sommario):
Small bacterial genomes are believed to be evolutionarily derived from larger genomes through massive loss of genes and are usually associated with symbiotic or pathogenic lifestyles. It is therefore intriguing that a similar phenomenon of genome reduction has been reported within a group of free-living phototrophic marine cyanobacteria Prochlorococcus. Here I have investigated the roles of natural selection and mutation rate in the process of Prochlorococcus genome size reduction. Using a data set of complete cyanobacterial genomes including 12 Prochlorococcus and a sister group of 5 marine Synechococcus , I first reconstructed the steps leading to Prochlorococcus genome reduction in a phylogenetic context. The result reveals that small genome sizes within Prochlorococcus were largely determined by massive gene loss shortly after the split of Prochlorococcus and Synechococcus (a process we refer to as early genome reduction). A maximum likelihood approach was then used to estimate changes in both selection effect and mutation rate in the evolutionary history of Prochlorococcus. I also examined the effect of selection and functional importance of a subset of ancestor-derived genes those are lost in Prochlorococcus but are still retained in the genomes of its sister Synechococcus group. It appears that the effect of purifying selection was strongest when a large number of small effect genes were deleted from nearly all functional categories. And during this period, mutation rate also accelerated. Based on these results, I propose that shortly after Prochlorococcus diverged from its common ancestor with marine Synechococcus, its population size increased quickly and thus the efficacy of selection became very high. Due to limited nutrients and relatively constant environment, selection favored a streamlined genome for maximum economies in material and energy, causing subsequent reduction in genome size and possibly also contributing to the observed higher mutation rate.
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Keller, Thomas E. "The evolution of RNA and the actin protein family". Thesis, 2012. http://hdl.handle.net/2152/30391.
Abstract (sommario):
In my dissertation I have broadly studied the evolution of RNA as well as the phylogenetic history of the actin protein family. In the first chapter I examined how various evolutionary processes interact at high mutation rates, which led to simple prediction based on the strength of selection. In the second chapter, I tested mRNA secondary structure stability at the beginning of genes as a way of identifying whether putative genes might be functional or not. Finally, I reconstructed the phylogenetic history of the actin protein family in vertebrates, revealing that a novel isoform is actively evolving in contrast to the remaining protein isoforms.
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Kvikstad, Erika Marit Makova Kateryna. "Mechanisms of insertion and deletion mutations rate variation, context specificity, and impact on primate sex chromosome evolution /". 2009. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-4351/index.html.