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"Genome evolution"
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Rapid genome reshaping by multiple-gene loss after whole-genome duplication in teleost fish suggested by mathematical modeling
Whole-genome duplication (WGD) is believed to be a significant source of major evolutionary innovation. Redundant genes resulting from WGD are thought to be lost or acquire new functions. However, the rates of gene loss and thus temporal process of genome reshaping after WGD remain unclear. The WGD shared by all teleost fish, one-half of all jawed vertebrates, was more recent than the two ancient WGDs that occurred before the origin of jawed vertebrates, and thus lends itself to analysis of gene loss and genome reshaping. Using a newly developed orthology identification pipeline, we inferred the post–teleost-specific WGD evolutionary histories of 6,892 protein-coding genes from nine phylogenetically representative teleost genomes on a time-calibrated tree. We found that rapid gene loss did occur in the first 60 My, with a loss of more than 70–80% of duplicated genes, and produced similar genomic gene arrangements within teleosts in that relatively short time. Mathematical modeling suggests that rapid gene loss occurred mainly by events involving simultaneous loss of multiple genes. We found that the subsequent 250 My were characterized by slow and steady loss of individual genes. Our pipeline also identified about 1,100 shared single-copy genes that are inferred to have become singletons before the divergence of clupeocephalan teleosts. Therefore, our comparative genome analysis suggests that rapid gene loss just after the WGD reshaped teleost genomes before the major divergence, and provides a useful set of marker genes for future phylogenetic analysis.
Journal Article
Neanderthal man : in search of lost genomes
\"What can we learn from the genes of our closest evolutionary relatives? Neanderthal Man tells the story of geneticist Svante Pääbo's mission to answer that question, beginning with the study of DNA in Egyptian mummies in the early 1980s and culminating in his sequencing of the Neanderthal genome in 2009. From Pääbo, we learn how Neanderthal genes offer a unique window into the lives of our hominin relatives and may hold the key to unlocking the mystery of why humans survived while Neanderthals went extinct. Drawing on genetic and fossil clues, Pääbo explores what is known about the origin of modern humans and their relationship to the Neanderthals and describes the fierce debate surrounding the nature of the two species' interactions. A riveting story about a visionary researcher and the nature of scientific inquiry, Neanderthal Man offers rich insight into the fundamental question of who we are\"-- Provided by publisher.
Book
Contrasting evolutionary trajectories of multiple retrotransposons following independent allopolyploidy in wild wheats
Transposable elements (TEs) are expectedly central to genome evolution. To assess the impact of TEs in driving genome turnover, we used allopolyploid genomes, showing considerable deviation from the predicted additivity of their diploid progenitors and thus having undergone major restructuring. Genome survey sequencing was used to select 17 putatively active families of long terminal repeat retrotransposons. Genome‐wide TE insertions were genotyped with sequence‐specific amplified polymorphism (SSAP) in diploid progenitors and their derived polyploids, and compared with changes in random sequences to assess restructuring of four independent Aegilops allotetraploid genomes. Generally, TEs with different evolutionary trajectories from those of random sequences were identified. Thus, TEs presented family‐specific and species‐specific dynamics following polyploidy, as illustrated by Sabine showing proliferation in particular polyploids, but massive elimination in others. Contrasting with that, only a few families (BARE1 and Romani) showed proliferation in all polyploids. Overall, TE divergence between progenitors was strongly correlated with the degree of restructuring in polyploid TE fractions. TE families present evolutionary trajectories that are decoupled from genome‐wide changes after allopolyploidy and have a pervasive impact on their restructuring.
Journal Article
Inside the human genome : a case for non-intelligent design
How do you explain flaw in a world engineered by God? Avise extends this age-old question to the most basic aspect of humanity's physical evidence-- our genes-- and provides the evolutionary answers.
Book
Selection at a genomic region of major effect is responsible for evolution of complex life histories in anadromous steelhead
Background
Disparity in the timing of biological events occurs across a variety of systems, yet the understanding of genetic basis underlying diverse phenologies remains limited. Variation in maturation timing occurs in steelhead trout, which has been associated with
greb1L
, an oestrogen target gene. Previous techniques that identified this gene only accounted for about 0.5–2.0% of the genome and solely investigated coastal populations, leaving uncertainty on the genetic basis of this trait and its prevalence across a larger geographic scale.
Results
We used a three-tiered approach to interrogate the genomic basis of complex phenology in anadromous steelhead. First, fine scale mapping with 5.3 million SNPs from resequencing data covering 68% of the genome confirmed a 309-kb region consisting of four genes on chromosome 28, including
greb1L
, to be the genomic region of major effect for maturation timing. Second, broad-scale characterization of candidate
greb1L
genotypes across 59 populations revealed unexpected patterns in maturation phenology for inland fish migrating long distances relative to those in coastal streams. Finally, genotypes from 890 PIT-tag tracked steelhead determined associations with early versus late arrival to spawning grounds that were previously unknown.
Conclusions
This study clarifies the genetic bases for disparity in phenology observed in steelhead, determining an unanticipated trait association with premature versus mature arrival to spawning grounds and identifying multiple candidate genes potentially contributing to this variation from a single genomic region of major effect. This illustrates how dense genome mapping and detailed phenotypic characterization can clarify genotype to phenotype associations across geographic ranges of species.
Journal Article
The Scale of Population Structure in Arabidopsis thaliana
The population structure of an organism reflects its evolutionary history and influences its evolutionary trajectory. It constrains the combination of genetic diversity and reveals patterns of past gene flow. Understanding it is a prerequisite for detecting genomic regions under selection, predicting the effect of population disturbances, or modeling gene flow. This paper examines the detailed global population structure of Arabidopsis thaliana. Using a set of 5,707 plants collected from around the globe and genotyped at 149 SNPs, we show that while A. thaliana as a species self-fertilizes 97% of the time, there is considerable variation among local groups. This level of outcrossing greatly limits observed heterozygosity but is sufficient to generate considerable local haplotypic diversity. We also find that in its native Eurasian range A. thaliana exhibits continuous isolation by distance at every geographic scale without natural breaks corresponding to classical notions of populations. By contrast, in North America, where it exists as an exotic species, A. thaliana exhibits little or no population structure at a continental scale but local isolation by distance that extends hundreds of km. This suggests a pattern for the development of isolation by distance that can establish itself shortly after an organism fills a new habitat range. It also raises questions about the general applicability of many standard population genetics models. Any model based on discrete clusters of interchangeable individuals will be an uneasy fit to organisms like A. thaliana which exhibit continuous isolation by distance on many scales.
Journal Article
The Evolutionary Dynamics of Repetitive DNA and Its Impact on the Genome Diversification in the Genus Sorghum
Polyploidization is an evolutionary event leading to structural changes of the genome(s), particularly allopolyploidization, which combines different genomes of distinct species. The tetraploid species, Sorghum halepense , is assumed an allopolyploid species formed by hybridization between diploid S. bicolor and S. propinquum . The repeat profiles of S. bicolor , S. halepense , and their relatives were compared to elucidate the repeats’ role in shaping their genomes. The repeat frequencies and profiles of the three diploid accessions ( S. bicolor , S. bicolor ssp. verticilliflorum , and S. bicolor var. technicum ) and two tetraploid accessions ( S. halepense ) are similar. However, the polymorphic distribution of the subtelomeric satellites preferentially enriched in the tetraploid S. halepense indicates drastic genome rearrangements after the allopolyploidization event. Verified by CENH3 chromatin immunoprecipitation (ChIP)-sequencing and fluorescence in situ hybridization (FISH) analysis the centromeres of S. bicolor are mainly composed of the abundant satellite SorSat137 (CEN38) and diverse CRMs, Athila of Ty3_gypsy and Ty1_copia-SIRE long terminal repeat (LTR) retroelements. A similar centromere composition was found in S. halepense . The potential contribution of S. bicolor in the formation of tetraploid S. halepense is discussed.
Journal Article
The Role of bZIP Transcription Factors in Green Plant Evolution: Adaptive Features Emerging from Four Founder Genes
Transcription factors of the basic leucine zipper (bZIP) family control important processes in all eukaryotes. In plants, bZIPs are regulators of many central developmental and physiological processes including photomorphogenesis, leaf and seed formation, energy homeostasis, and abiotic and biotic stress responses. Here we performed a comprehensive phylogenetic analysis of bZIP genes from algae, mosses, ferns, gymnosperms and angiosperms.
We identified 13 groups of bZIP homologues in angiosperms, three more than known before, that represent 34 Possible Groups of Orthologues (PoGOs). The 34 PoGOs may correspond to the complete set of ancestral angiosperm bZIP genes that participated in the diversification of flowering plants. Homologous genes dedicated to seed-related processes and ABA-mediated stress responses originated in the common ancestor of seed plants, and three groups of homologues emerged in the angiosperm lineage, of which one group plays a role in optimizing the use of energy.
Our data suggest that the ancestor of green plants possessed four bZIP genes functionally involved in oxidative stress and unfolded protein responses that are bZIP-mediated processes in all eukaryotes, but also in light-dependent regulations. The four founder genes amplified and diverged significantly, generating traits that benefited the colonization of new environments.
Journal Article
The ash dieback invasion of Europe was founded by two genetically divergent individuals
Accelerating international trade and climate change make pathogen spread an increasing concern.
Hymenoscyphus fraxineus
, the causal agent of ash dieback, is a fungal pathogen that has been moving across continents and hosts from Asian to European ash. Most European common ash trees (
Fraxinus excelsior
) are highly susceptible to
H.
fraxineus
, although a minority (~5%) have partial resistance to dieback. Here, we assemble and annotate a
H.
fraxineus
draft genome, which approaches chromosome scale. Pathogen genetic diversity across Europe and in Japan, reveals a strong bottleneck in Europe, though a signal of adaptive diversity remains in key host interaction genes. We find that the European population was founded by two divergent haploid individuals. Divergence between these haplotypes represents the ancestral polymorphism within a large source population. Subsequent introduction from this source would greatly increase adaptive potential of the pathogen. Thus, further introgression of
H.
fraxineus
into Europe represents a potential threat and Europe-wide biological security measures are needed to manage this disease.
The fungal pathogen
Hymenoscyphus fraxineus
is killing European common ash trees. Here, the authors sequence the genome of
H. fraxineus
and show that European populations were founded by two divergent haploid individuals introduced from Asia.
Journal Article