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Parallel Evolution of Sex-Linked Genes across XX/XY and ZZ/ZW Sex Chromosome Systems in the Frog Glandirana rugosa. Genes (Basel) 2023; 14:genes14020257. [PMID: 36833183 PMCID: PMC9956060 DOI: 10.3390/genes14020257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2022] [Revised: 01/15/2023] [Accepted: 01/16/2023] [Indexed: 01/20/2023] Open
Abstract
Genetic sex-determination features male (XX/XY) or female heterogamety (ZZ/ZW). To identify similarities and differences in the molecular evolution of sex-linked genes between these systems, we directly compared the sex chromosome systems existing in the frog Glandirana rugosa. The heteromorphic X/Y and Z/W sex chromosomes were derived from chromosomes 7 (2n = 26). RNA-Seq, de novo assembly, and BLASTP analyses identified 766 sex-linked genes. These genes were classified into three different clusters (XW/YZ, XY/ZW, and XZ/YW) based on sequence identities between the chromosomes, probably reflecting each step of the sex chromosome evolutionary history. The nucleotide substitution per site was significantly higher in the Y- and Z-genes than in the X- and W- genes, indicating male-driven mutation. The ratio of nonsynonymous to synonymous nucleotide substitution rates was higher in the X- and W-genes than in the Y- and Z-genes, with a female bias. Allelic expression in gonad, brain, and muscle was significantly higher in the Y- and W-genes than in the X- and Z-genes, favoring heterogametic sex. The same set of sex-linked genes showed parallel evolution across the two distinct systems. In contrast, the unique genomic region of the sex chromosomes demonstrated a difference between the two systems, with even and extremely high expression ratios of W/Z and Y/X, respectively.
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2
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Wilson J, Staley JM, Wyckoff GJ. Extinction of chromosomes due to specialization is a universal occurrence. Sci Rep 2020; 10:2170. [PMID: 32034231 PMCID: PMC7005762 DOI: 10.1038/s41598-020-58997-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2019] [Accepted: 01/20/2020] [Indexed: 11/09/2022] Open
Abstract
The human X and Y chromosomes evolved from a pair of autosomes approximately 180 million years ago. Despite their shared evolutionary origin, extensive genetic decay has resulted in the human Y chromosome losing 97% of its ancestral genes while gene content and order remain highly conserved on the X chromosome. Five 'stratification' events, most likely inversions, reduced the Y chromosome's ability to recombine with the X chromosome across the majority of its length and subjected its genes to the erosive forces associated with reduced recombination. The remaining functional genes are ubiquitously expressed, functionally coherent, dosage-sensitive genes, or have evolved male-specific functionality. It is unknown, however, whether functional specialization is a degenerative phenomenon unique to sex chromosomes, or if it conveys a potential selective advantage aside from sexual antagonism. We examined the evolution of mammalian orthologs to determine if the selective forces that led to the degeneration of the Y chromosome are unique in the genome. The results of our study suggest these forces are not exclusive to the Y chromosome, and chromosomal degeneration may have occurred throughout our evolutionary history. The reduction of recombination could additionally result in rapid fixation through isolation of specialized functions resulting in a cost-benefit relationship during times of intense selective pressure.
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Affiliation(s)
- Jason Wilson
- University of Missouri-Kansas City School of Medicine, Department of Biomedical and Health Informatics, Kansas City, 64108, Missouri, USA.
| | - Joshua M Staley
- Kansas State University College of Veterinary Medicine, Department of Diagnostic Medicine/Pathobiology, Olathe, 66061, Kansas, USA
| | - Gerald J Wyckoff
- University of Missouri-Kansas City School of Medicine, Department of Biomedical and Health Informatics, Kansas City, 64108, Missouri, USA.,Kansas State University College of Veterinary Medicine, Department of Diagnostic Medicine/Pathobiology, Olathe, 66061, Kansas, USA.,University of Missouri-Kansas City School of Biological and Chemical Sciences, Department of Molecular Biology and Biochemistry, Kansas City, 64108, Missouri, USA
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3
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The Evolution of Unusually Small Amelogenin Genes in Cetaceans; Pseudogenization, X-Y Gene Conversion, and Feeding Strategy. J Mol Evol 2019; 88:122-135. [PMID: 31754761 DOI: 10.1007/s00239-019-09917-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2019] [Accepted: 11/08/2019] [Indexed: 12/11/2022]
Abstract
Among extant cetaceans, mysticetes are filter feeders that do not possess teeth and use their baleen for feeding, while most odontocetes are considered suction feeders, which capture prey by suction without biting or chewing with teeth. In the present study, we address the functionality of amelogenin (AMEL) genes in cetaceans. AMEL encodes a protein that is specifically involved in dental enamel formation and is located on the sex chromosomes in eutherians. The X-copy AMELX is functional in enamel-bearing eutherians, whereas the Y-copy AMELY appears to have undergone decay and was completely lost in some species. Consistent with these premises, we detected various deleterious mutations and/or non-canonical splice junctions in AMELX of mysticetes and four suction feeding odontocetes, Delphinapterus leucas, Monodon monoceros, Kogia breviceps, and Physeter macrocephalus, and in AMELY of mysticetes and odontocetes. Regardless of the functionality, both AMELX and AMELY are equally and unusually small in cetaceans, and even their functional AMELX genes presumably encode a degenerate core region, which is thought to be essential for enamel matrix assembly and enamel crystal growth. Furthermore, our results suggest that the most recent common ancestors of extant cetaceans had functional AMELX and AMELY, both of which are similar to AMELX of Platanista minor. Similar small AMELX and AMELY in archaic cetaceans can be explained by gene conversion between AMELX and AMELY. We speculate that common ancestors of modern cetaceans employed a degenerate AMELX, transferred from a decaying AMELY by gene conversion, at an early stage of their transition to suction feeders.
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4
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Peneder P, Wallner B, Vogl C. Exchange of genetic information between therian X and Y chromosome gametologs in old evolutionary strata. Ecol Evol 2017; 7:8478-8487. [PMID: 29075464 PMCID: PMC5648654 DOI: 10.1002/ece3.3278] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Revised: 06/29/2017] [Accepted: 06/30/2017] [Indexed: 11/24/2022] Open
Abstract
Therian X and Y sex chromosomes arose from a pair of autosomes. Y chromosomes consist of a pseudoautosomal region that crosses over with the X chromosome and a male‐specific Y‐chromosomal region that does not. The X chromosome can be structured into “evolutionary strata”. Divergence of X‐chromosomal genes from their gametologs is similar within a stratum, but differs among strata, likely caused by a different onset of suppression of crossing over between gametologs. After stratum formation, exchange of information between gametologs has long been believed absent; however, recent studies have shown limited exchange, likely through gene conversion. Herein we investigate exchange of genetic information between gametologs in old strata that formed before the split of Laurasiatheria (cattle) from Euarchontoglires (primates and rodents) with a new phylogenetic approach. A prerequisite for our test is an overall preradiative topology, that is, all X‐chromosomal gametologs are more similar among themselves than to Y‐chromosomal sequences. Screening multiple sequence alignments of the coding sequences of genes from cattle, mice, and humans identified four genes, DDX3X/Y,RBMX/Y,USP9X/Y, and UTX/Y, exhibiting a preradiation topology. Applying our test, we detected exchange of genetic information between all four X and Y gametologs after stratum formation.
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Affiliation(s)
- Peter Peneder
- Institut für Tierzucht und Genetik Veterinärmedizinische Universität Wien Vienna Austria.,Department für Mikrobiologie, Immunbiologie und Genetik Zentrum für Molekulare Biologie Universität Wien Vienna Austria
| | - Barbara Wallner
- Institut für Tierzucht und Genetik Veterinärmedizinische Universität Wien Vienna Austria
| | - Claus Vogl
- Institut für Tierzucht und Genetik Veterinärmedizinische Universität Wien Vienna Austria
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5
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flyDIVaS: A Comparative Genomics Resource for Drosophila Divergence and Selection. G3-GENES GENOMES GENETICS 2016; 6:2355-63. [PMID: 27226167 PMCID: PMC4978890 DOI: 10.1534/g3.116.031138] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
With arguably the best finished and expertly annotated genome assembly, Drosophila melanogaster is a formidable genetics model to study all aspects of biology. Nearly a decade ago, the 12 Drosophila genomes project expanded D. melanogaster’s breadth as a comparative model through the community-development of an unprecedented genus- and genome-wide comparative resource. However, since its inception, these datasets for evolutionary inference and biological discovery have become increasingly outdated, outmoded, and inaccessible. Here, we provide an updated and upgradable comparative genomics resource of Drosophila divergence and selection, flyDIVaS, based on the latest genomic assemblies, curated FlyBase annotations, and recent OrthoDB orthology calls. flyDIVaS is an online database containing D. melanogaster-centric orthologous gene sets, CDS and protein alignments, divergence statistics (% gaps, dN, dS, dN/dS), and codon-based tests of positive Darwinian selection. Out of 13,920 protein-coding D. melanogaster genes, ∼80% have one aligned ortholog in the closely related species, D. simulans, and ∼50% have 1–1 12-way alignments in the original 12 sequenced species that span over 80 million yr of divergence. Genes and their orthologs can be chosen from four different taxonomic datasets differing in phylogenetic depth and coverage density, and visualized via interactive alignments and phylogenetic trees. Users can also batch download entire comparative datasets. A functional survey finds conserved mitotic and neural genes, highly diverged immune and reproduction-related genes, more conspicuous signals of divergence across tissue-specific genes, and an enrichment of positive selection among highly diverged genes. flyDIVaS will be regularly updated and can be freely accessed at www.flydivas.info. We encourage researchers to regularly use this resource as a tool for biological inference and discovery, and in their classrooms to help train the next generation of biologists to creatively use such genomic big data resources in an integrative manner.
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6
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Singh ND, Koerich LB, Carvalho AB, Clark AG. Positive and purifying selection on the Drosophila Y chromosome. Mol Biol Evol 2014; 31:2612-23. [PMID: 24974375 DOI: 10.1093/molbev/msu203] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Y chromosomes, with their reduced effective population size, lack of recombination, and male-limited transmission, present a unique collection of constraints for the operation of natural selection. Male-limited transmission may greatly increase the efficacy of selection for male-beneficial mutations, but the reduced effective size also inflates the role of random genetic drift. Together, these defining features of the Y chromosome are expected to influence rates and patterns of molecular evolution on the Y as compared with X-linked or autosomal loci. Here, we use sequence data from 11 genes in 9 Drosophila species to gain insight into the efficacy of natural selection on the Drosophila Y relative to the rest of the genome. Drosophila is an ideal system for assessing the consequences of Y-linkage for molecular evolution in part because the gene content of Drosophila Y chromosomes is highly dynamic, with orthologous genes being Y-linked in some species whereas autosomal in others. Our results confirm the expectation that the efficacy of natural selection at weakly selected sites is reduced on the Y chromosome. In contrast, purifying selection on the Y chromosome for strongly deleterious mutations does not appear to be compromised. Finally, we find evidence of recurrent positive selection for 4 of the 11 genes studied here. Our results thus highlight the variable nature of the mode and impact of natural selection on the Drosophila Y chromosome.
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Affiliation(s)
- Nadia D Singh
- Department of Biological Sciences, North Carolina State University
| | - Leonardo B Koerich
- Departamento de Genética, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | | | - Andrew G Clark
- Department of Molecular Biology and Genetics, Cornell University
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Goldstein RA. Population size dependence of fitness effect distribution and substitution rate probed by biophysical model of protein thermostability. Genome Biol Evol 2014; 5:1584-93. [PMID: 23884461 PMCID: PMC3787666 DOI: 10.1093/gbe/evt110] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The predicted effect of effective population size on the distribution of fitness effects and substitution rate is critically dependent on the relationship between sequence and fitness. This highlights the importance of using models that are informed by the molecular biology, biochemistry, and biophysics of the evolving systems. We describe a computational model based on fundamental aspects of biophysics, the requirement for (most) proteins to be thermodynamically stable. Using this model, we find that differences in population size have minimal impact on the distribution of population-scaled fitness effects, as well as on the rate of molecular evolution. This is because larger populations result in selection for more stable proteins that are less affected by mutations. This reduction in the magnitude of the fitness effects almost exactly cancels the greater selective pressure resulting from the larger population size. Conversely, changes in the population size in either direction cause transient increases in the substitution rate. As differences in population size often correspond to changes in population size, this makes comparisons of substitution rates in different lineages difficult to interpret.
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Affiliation(s)
- Richard A Goldstein
- Division of Infection and Immunity, University College London, United Kingdom
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Lanfear R, Kokko H, Eyre-Walker A. Population size and the rate of evolution. Trends Ecol Evol 2013; 29:33-41. [PMID: 24148292 DOI: 10.1016/j.tree.2013.09.009] [Citation(s) in RCA: 244] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Revised: 09/04/2013] [Accepted: 09/16/2013] [Indexed: 11/28/2022]
Abstract
Does evolution proceed faster in larger or smaller populations? The relationship between effective population size (Ne) and the rate of evolution has consequences for our ability to understand and interpret genomic variation, and is central to many aspects of evolution and ecology. Many factors affect the relationship between Ne and the rate of evolution, and recent theoretical and empirical studies have shown some surprising and sometimes counterintuitive results. Some mechanisms tend to make the relationship positive, others negative, and they can act simultaneously. The relationship also depends on whether one is interested in the rate of neutral, adaptive, or deleterious evolution. Here, we synthesize theoretical and empirical approaches to understanding the relationship and highlight areas that remain poorly understood.
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Affiliation(s)
- Robert Lanfear
- Ecology Evolution and Genetics, Research School of Biology, Australian National University, Canberra, ACT, Australia; National Evolutionary Synthesis Center, Durham, NC, USA.
| | - Hanna Kokko
- Ecology Evolution and Genetics, Research School of Biology, Australian National University, Canberra, ACT, Australia
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9
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Blaser O, Grossen C, Neuenschwander S, Perrin N. SEX-CHROMOSOME TURNOVERS INDUCED BY DELETERIOUS MUTATION LOAD. Evolution 2012; 67:635-45. [DOI: 10.1111/j.1558-5646.2012.01810.x] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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10
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Muyle A, Zemp N, Deschamps C, Mousset S, Widmer A, Marais GAB. Rapid de novo evolution of X chromosome dosage compensation in Silene latifolia, a plant with young sex chromosomes. PLoS Biol 2012; 10:e1001308. [PMID: 22529744 PMCID: PMC3328428 DOI: 10.1371/journal.pbio.1001308] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2011] [Accepted: 03/01/2012] [Indexed: 11/18/2022] Open
Abstract
Silene latifolia is a dioecious plant with heteromorphic sex chromosomes that have originated only ∼10 million years ago and is a promising model organism to study sex chromosome evolution in plants. Previous work suggests that S. latifolia XY chromosomes have gradually stopped recombining and the Y chromosome is undergoing degeneration as in animal sex chromosomes. However, this work has been limited by the paucity of sex-linked genes available. Here, we used 35 Gb of RNA-seq data from multiple males (XY) and females (XX) of an S. latifolia inbred line to detect sex-linked SNPs and identified more than 1,700 sex-linked contigs (with X-linked and Y-linked alleles). Analyses using known sex-linked and autosomal genes, together with simulations indicate that these newly identified sex-linked contigs are reliable. Using read numbers, we then estimated expression levels of X-linked and Y-linked alleles in males and found an overall trend of reduced expression of Y-linked alleles, consistent with a widespread ongoing degeneration of the S. latifolia Y chromosome. By comparing expression intensities of X-linked alleles in males and females, we found that X-linked allele expression increases as Y-linked allele expression decreases in males, which makes expression of sex-linked contigs similar in both sexes. This phenomenon is known as dosage compensation and has so far only been observed in evolutionary old animal sex chromosome systems. Our results suggest that dosage compensation has evolved in plants and that it can quickly evolve de novo after the origin of sex chromosomes.
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Affiliation(s)
- Aline Muyle
- Laboratoire de Biométrie et Biologie Evolutive (UMR 5558), CNRS/Université Lyon 1, Villeurbanne, France
| | - Niklaus Zemp
- Institute of Integrative Biology (IBZ), ETH Zurich, Zürich, Switzerland
| | | | - Sylvain Mousset
- Laboratoire de Biométrie et Biologie Evolutive (UMR 5558), CNRS/Université Lyon 1, Villeurbanne, France
| | - Alex Widmer
- Institute of Integrative Biology (IBZ), ETH Zurich, Zürich, Switzerland
- * E-mail: (GABM); (AW)
| | - Gabriel A. B. Marais
- Laboratoire de Biométrie et Biologie Evolutive (UMR 5558), CNRS/Université Lyon 1, Villeurbanne, France
- * E-mail: (GABM); (AW)
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11
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Dannemann M, Prüfer K, Lizano E, Nickel B, Burbano HA, Kelso J. Transcription factors are targeted by differentially expressed miRNAs in primates. Genome Biol Evol 2012; 4:552-64. [PMID: 22454130 PMCID: PMC3342879 DOI: 10.1093/gbe/evs033] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
MicroRNAs (miRNAs) are small RNA molecules involved in the regulation of mammalian gene expression. Together with other transcription regulators, miRNAs modulate the expression of genes and thereby potentially contribute to tissue and species diversity. To identify miRNAs that are differentially expressed between tissues and/or species, and the genes regulated by these, we have quantified expression of miRNAs and messenger RNAs in five tissues from multiple human, chimpanzee, and rhesus macaque individuals using high-throughput sequencing. The breadth of this tissue and species data allows us to show that downregulation of target genes by miRNAs is more pronounced between tissues than between species and that downregulation is more pronounced for genes with fewer binding sites for expressed miRNAs. Intriguingly, we find that tissue- and species-specific miRNAs target transcription factor genes (TFs) significantly more often than expected. Through their regulatory effect on transcription factors, miRNAs may therefore exert an indirect influence on a larger proportion of genes than previously thought.
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Affiliation(s)
- Michael Dannemann
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
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12
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Gossmann TI, Keightley PD, Eyre-Walker A. The effect of variation in the effective population size on the rate of adaptive molecular evolution in eukaryotes. Genome Biol Evol 2012; 4:658-67. [PMID: 22436998 PMCID: PMC3381672 DOI: 10.1093/gbe/evs027] [Citation(s) in RCA: 110] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The role of adaptation is a fundamental question in molecular evolution. Theory predicts that species with large effective population sizes should undergo a higher rate of adaptive evolution than species with low effective population sizes if adaptation is limited by the supply of mutations. Previous analyses have appeared to support this conjecture because estimates of the proportion of nonsynonymous substitutions fixed by adaptive evolution, α, tend to be higher in species with large Ne. However, α is a function of both the number of advantageous and effectively neutral substitutions, either of which might depend on Ne. Here, we investigate the relationship between Ne and ωa, the rate of adaptive evolution relative to the rate of neutral evolution, using nucleotide polymorphism and divergence data from 13 independent pairs of eukaryotic species. We find a highly significant positive correlation between ωa and Ne. We also find some evidence that the rate of adaptive evolution varies between groups of organisms for a given Ne. The correlation between ωa and Ne does not appear to be an artifact of demographic change or selection on synonymous codon use. Our results suggest that adaptation is to some extent limited by the supply of mutations and that at least some adaptation depends on newly occurring mutations rather than on standing genetic variation. Finally, we show that the proportion of nearly neutral nonadaptive substitutions declines with increasing Ne. The low rate of adaptive evolution and the high proportion of effectively neutral substitution in species with small Ne are expected to combine to make it difficult to detect adaptive molecular evolution in species with small Ne.
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Affiliation(s)
- Toni I Gossmann
- School of Life Sciences, University of Sussex, Brighton, United Kingdom
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13
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Tsend-Ayush E, Kortschak RD, Bernard P, Lim SL, Ryan J, Rosenkranz R, Borodina T, Dohm JC, Himmelbauer H, Harley VR, Grützner F. Identification of mediator complex 26 (Crsp7) gametologs on platypus X1 and Y5 sex chromosomes: a candidate testis-determining gene in monotremes? Chromosome Res 2012; 20:127-38. [DOI: 10.1007/s10577-011-9270-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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14
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Abstract
The effective population size (N(e)) is one of the most fundamental parameters in population genetics. It is thought to vary across the genome as a consequence of differences in the rate of recombination and the density of selected sites due to the processes of genetic hitchhiking and background selection. Although it is known that there is intragenomic variation in the effective population size in some species, it is not known whether this is widespread or how much variation in the effective population size there is. Here, we test whether the effective population size varies across the genome, between protein-coding genes, in 10 eukaryotic species by considering whether there is significant variation in neutral diversity, taking into account differences in the mutation rate between loci by using the divergence between species. In most species we find significant evidence of variation. We investigate whether the variation in N(e) is correlated to recombination rate and the density of selected sites in four species, for which these data are available. We find that N(e) is positively correlated to recombination rate in one species, Drosophila melanogaster, and negatively correlated to a measure of the density of selected sites in two others, humans and Arabidopsis thaliana. However, much of the variation remains unexplained. We use a hierarchical Bayesian analysis to quantify the amount of variation in the effective population size and show that it is quite modest in all species-most genes have an N(e) that is within a few fold of all other genes. Nonetheless we show that this modest variation in N(e) is sufficient to cause significant differences in the efficiency of natural selection across the genome, by demonstrating that the ratio of the number of nonsynonymous to synonymous polymorphisms is significantly correlated to synonymous diversity and estimates of N(e), even taking into account the obvious nonindependence between these measures.
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15
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Evidence of the accumulation of allele-specific non-synonymous substitutions in the young region of recombination suppression within the mating-type chromosomes of Neurospora tetrasperma. Heredity (Edinb) 2011; 107:305-14. [PMID: 21386869 DOI: 10.1038/hdy.2011.11] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Currently, little is known about the origin and early evolution of sex chromosomes. This is largely due to the fact that ancient non-recombining sex chromosomes are highly degenerated, and thus provide little information about the early genomic events in their evolution. The Neurospora tetrasperma mating-type (mat) chromosomes contain a young (<6 Mya) and large region (>6.6 Mb) of suppressed recombination, thereby providing a model system to study early stages of sex chromosome evolution. Here, we examined alleles of 207 genes located on the N. tetrasperma mat a and mat A chromosomes to test for signs of genomic alterations at the protein level in the young region of recombination suppression. We report that the N. tetrasperma mat a and mat A chromosomes have each independently accumulated allele-specific non-synonymous codon substitutions in a time-dependent, and gene-specific manner in the recombinationally suppressed region. In addition, examination of the ratio (ω) of non-synonymous substitutions (dN) to synonymous substitutions (dS) using maximum likelihood analyses, indicates that such changes are associated with relaxed purifying selection, a finding consistent with genomic degeneration. We also reveal that sex specific biases in mutation rates or selection pressures are not necessary for genomic alterations in sex chromosomes, and that recombination suppression in itself is sufficient to explain these results. The present findings extend our current understanding of genomic events associated within the young region of recombination suppression in these fungal sex-regulating chromosomes.
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16
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Wu GC, Joron M, Jiggins CD. Signatures of selection in loci governing major colour patterns in Heliconius butterflies and related species. BMC Evol Biol 2010; 10:368. [PMID: 21114846 PMCID: PMC3001726 DOI: 10.1186/1471-2148-10-368] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2010] [Accepted: 11/29/2010] [Indexed: 11/18/2022] Open
Abstract
Background Protein-coding change is one possible genetic mechanism underlying the evolution of adaptive wing colour pattern variation in Heliconius butterflies. Here we determine whether 38 putative genes within two major Heliconius patterning loci, HmYb and HmB, show evidence of positive selection. Ratios of nonsynonymous to synonymous nucleotide changes (ω) were used to test for selection, as a means of identifying candidate genes within each locus that control wing pattern. Results Preliminary analyses using 454 transcriptome and Bacterial Artificial Chromosome (BAC) sequences from three Heliconius species highlighted a cluster of genes within each region showing relatively higher rates of sequence evolution. Other genes within the region appear to be highly constrained, and no ω estimates exceeded one. Three genes from each locus with the highest average pairwise ω values were amplified from additional Heliconius species and races. Two selected genes, fizzy-like (HmYb) and DALR (HmB), were too divergent for amplification across species and were excluded from further analysis. Amongst the remaining genes, HM00021 and Kinesin possessed the highest background ω values within the HmYb and HmB loci, respectively. After accounting for recombination, these two genes both showed evidence of having codons with a signature of selection, although statistical support for this signal was not strong in any case. Conclusions Tests of selection reveal a cluster of candidate genes in each locus, suggesting that weak directional selection may be occurring within a small region of each locus, but coding changes alone are unlikely to explain the full range of wing pattern diversity. These analyses pinpoint many of the same genes believed to be involved in the control of colour patterning in Heliconius that have been identified through other studies implementing different research methods.
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Affiliation(s)
- Grace C Wu
- Department of Zoology, University of Cambridge, UK
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17
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Park C, Carrel L, Makova KD. Strong purifying selection at genes escaping X chromosome inactivation. Mol Biol Evol 2010; 27:2446-50. [PMID: 20534706 DOI: 10.1093/molbev/msq143] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
To achieve dosage balance of X-linked genes between mammalian males and females, one female X chromosome becomes inactivated. However, approximately 15% of genes on this inactivated chromosome escape X chromosome inactivation (XCI). Here, using a chromosome-wide analysis of primate X-linked orthologs, we test a hypothesis that such genes evolve under a unique selective pressure. We find that escape genes are subject to stronger purifying selection than inactivated genes and that positive selection does not significantly affect the evolution of these genes. The strength of selection does not differ between escape genes with similar versus different expression levels in males versus females. Intriguingly, escape genes possessing Y homologs evolve under the strongest purifying selection. We also found evidence of stronger conservation in gene expression levels in escape than inactivated genes. We hypothesize that divergence in function and expression between X and Y gametologs is driving such strong purifying selection for escape genes.
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Affiliation(s)
- Chungoo Park
- Center for Medical Genomics, Pennsylvania State University, University Park, USA
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18
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Hughes AL, Irausquin S, Friedman R. The evolutionary biology of poxviruses. INFECTION GENETICS AND EVOLUTION 2009; 10:50-9. [PMID: 19833230 DOI: 10.1016/j.meegid.2009.10.001] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2009] [Revised: 10/01/2009] [Accepted: 10/02/2009] [Indexed: 11/29/2022]
Abstract
The poxviruses (family Poxviridae) are a family of double-stranded viruses including several species that infect humans and their domestic animals, most notably Variola virus (VARV), the causative agent of smallpox. The evolutionary biology of these viruses poses numerous questions, for which we have only partial answers at present. Here we review evidence regarding the origin of poxviruses, the frequency of host transfer in poxvirus history, horizontal transfer of host genes to poxviruses, and the population processes accounting for patterns of nucleotide sequence polymorphism.
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Affiliation(s)
- Austin L Hughes
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA.
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Wilson MA, Makova KD. Evolution and survival on eutherian sex chromosomes. PLoS Genet 2009; 5:e1000568. [PMID: 19609352 PMCID: PMC2704370 DOI: 10.1371/journal.pgen.1000568] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Accepted: 06/18/2009] [Indexed: 11/19/2022] Open
Abstract
Since the two eutherian sex chromosomes diverged from an ancestral autosomal pair, the X has remained relatively gene-rich, while the Y has lost most of its genes through the accumulation of deleterious mutations in nonrecombining regions. Presently, it is unclear what is distinctive about genes that remain on the Y chromosome, when the sex chromosomes acquired their unique evolutionary rates, and whether X-Y gene divergence paralleled that of paralogs located on autosomes. To tackle these questions, here we juxtaposed the evolution of X and Y homologous genes (gametologs) in eutherian mammals with their autosomal orthologs in marsupial and monotreme mammals. We discovered that genes on the X and Y acquired distinct evolutionary rates immediately following the suppression of recombination between the two sex chromosomes. The Y-linked genes evolved at higher rates, while the X-linked genes maintained the lower evolutionary rates of the ancestral autosomal genes. These distinct rates have been maintained throughout the evolution of X and Y. Specifically, in humans, most X gametologs and, curiously, also most Y gametologs evolved under stronger purifying selection than similarly aged autosomal paralogs. Finally, after evaluating the current experimental data from the literature, we concluded that unique mRNA/protein expression patterns and functions acquired by Y (versus X) gametologs likely contributed to their retention. Our results also suggest that either the boundary between sex chromosome strata 3 and 4 should be shifted or that stratum 3 should be divided into two strata. Using recently available marsupial and monotreme genomes, we investigated nascent sex chromosome evolution in mammals. We show that, in eutherian mammals, X and Y genes acquired distinct evolutionary rates and functional constraints immediately after recombination suppression; X-linked genes maintained lower, ancestral (autosomal), rates, whereas the evolutionary rates of Y-linked genes increased. Most X and, unexpectedly, Y genes evolved under stronger purifying selection than similarly aged autosomal paralogs. However, we also observed that the divergence of gametologs and paralogs shared similar features. In addition, many Y-linked copies evolved unique functions and expression patterns compared to their counterparts on the X chromosome. Therefore, our results suggest that to be retained on the Y chromosome, genes need to acquire separately valuable expression and/or functions to be safeguarded by purifying selection.
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Affiliation(s)
- Melissa A. Wilson
- Department of Biology, Pennsylvania State University, University Park, Pennsylvania, United States of America
- Center for Comparative Genomics and Bioinformatics, Pennsylvania State University, University Park, Pennsylvania, United States of America
- The Integrative Biosciences Program, Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Kateryna D. Makova
- Department of Biology, Pennsylvania State University, University Park, Pennsylvania, United States of America
- Center for Comparative Genomics and Bioinformatics, Pennsylvania State University, University Park, Pennsylvania, United States of America
- The Integrative Biosciences Program, Pennsylvania State University, University Park, Pennsylvania, United States of America
- * E-mail:
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Hughes AL, Friedman R. More radical amino acid replacements in primates than in rodents: support for the evolutionary role of effective population size. Gene 2009; 440:50-6. [PMID: 19332110 DOI: 10.1016/j.gene.2009.03.012] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2009] [Revised: 03/16/2009] [Accepted: 03/19/2009] [Indexed: 02/04/2023]
Abstract
We examined the pattern of nucleotide substitution in 4933 conserved single-copy orthologous protein-coding genes of human, rhesus, mouse, and rat. Consistent with previous studies, the median ratio of the number of nonsynonymous substitutions per nonsynonymous site (d(N)) to the number of synonymous substitutions per synonymous site (d(S)) was significantly higher in the comparison between the two primates than in the comparison between the two rodents. This pattern was particularly strong in the case of genes expressed in the immune system, but also occurred in other genes, including a set of highly conserved genes involved in the regulation of transcription. Both synonymous and nonsynonymous differences occurred independently in the same codons in the primates and in the rodents to a greater extent than expected by chance, but the extent of the deviation from random expectation was much greater in the case of nonsynonymous differences. Parallel amino acid replacements occurred at the same sites in the primates and rodents far more frequently than expected by chance, but tended to involve very conservative amino acid changes. Divergent amino acid changes involved more chemically different amino acids than parallel changes, and divergent amino acid replacements between the primates were significantly more radical than those between the rodents. These results are most easily explained on the hypothesis that the evolution of these genes has been shaped largely by purifying selection, which has been less effective in primates than in rodents, presumably as a consequence of lower long-term effective population sizes in the former.
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Affiliation(s)
- Austin L Hughes
- Department of Biological Sciences, Coker Life Sciences Building, 715 Sumter St., University of South Carolina, Columbia SC 29208, USA.
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Hughes AL. Near neutrality: leading edge of the neutral theory of molecular evolution. Ann N Y Acad Sci 2008; 1133:162-79. [PMID: 18559820 DOI: 10.1196/annals.1438.001] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The nearly neutral theory represents a development of Kimura's neutral theory of molecular evolution that makes testable predictions that go beyond a mere null model. Recent evidence has strongly supported several of these predictions, including the prediction that slightly deleterious variants will accumulate in a species that has undergone a severe bottleneck or in cases where recombination is reduced or absent. Because bottlenecks often occur in speciation and slightly deleterious mutations in coding regions will usually be nonsynonymous, we should expect that the ratio of nonsynonymous to synonymous fixed differences between species should often exceed the ratio of nonsynonymous to synonymous polymorphisms within species. Many data support this prediction, although they have often been wrongly interpreted as evidence for positive Darwinian selection. The use of conceptually flawed tests for positive selection has become widespread in recent years, seriously harming the quest for an understanding of genome evolution. When properly analyzed, many (probably most) claimed cases of positive selection will turn out to involve the fixation of slightly deleterious mutations by genetic drift in bottlenecked populations. Slightly deleterious variants are a transient feature of evolution in the long term, but they have substantially affected contemporary species, including our own.
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Affiliation(s)
- Austin L Hughes
- Department of Biological Sciences, University of South Carolina, Coker Life Sciences Bldg., 700 Sumter St., Columbia, South Carolina 29208, USA.
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Hughes AL, Hughes MAK. More effective purifying selection on RNA viruses than in DNA viruses. Gene 2007; 404:117-25. [PMID: 17928171 DOI: 10.1016/j.gene.2007.09.013] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2007] [Revised: 09/11/2007] [Accepted: 09/13/2007] [Indexed: 01/11/2023]
Abstract
Analysis of the pattern of nucleotide diversity in 222 independent viral sequence datasets showed the prevalence of purifying selection. In spite of the higher mutation rate of RNA viruses, our analyses revealed stronger evidence of the action of purifying selection in RNA viruses than in DNA viruses. The ratio of nonsynonymous to synonymous nucleotide diversity was significantly lower in RNA viruses than in DNA viruses, indicating that nonsynonymous mutations have been removed at a greater rate (relative to the mutation rate) in the former than in the latter. Moreover, statistics that measure the occurrence of rare polymorphisms revealed significantly a greater excess of rare nonsynonymous polymorphisms in RNA viruses than in DNA viruses but no difference with respect to synonymous polymorphisms. Since rare nonsynonymous polymorphisms are likely to be undergoing the effects of purifying selection acting to eliminate them, this result implies a stronger signature of ongoing purifying selection in RNA viruses than in DNA viruses. Across datasets from both DNA viruses and RNA viruses, we found a negatively allometric relationship between nonsynonymous and synonymous nucleotide diversity; in other words, nonsynonymous nucleotide diversity increased with synonymous nucleotide diversity at a less than linear rate. These findings are most easily explained by the occurrence of slightly deleterious mutations. The fact that the negative allometry was more pronounced in RNA viruses than in DNA viruses provided additional evidence that purifying selection is more effective in the former than in the latter.
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Affiliation(s)
- Austin L Hughes
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29205, USA.
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Putze M, Nürnberg S, Fickel J. Y-chromosomal markers for the European brown hare (Lepus europaeus, Pallas 1778). EUR J WILDLIFE RES 2007. [DOI: 10.1007/s10344-007-0093-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Sandstedt SA, Tucker PK. Inefficient purifying selection: the mammalian Y chromosome in the rodent genus Mus. Mamm Genome 2006; 17:14-21. [PMID: 16416087 DOI: 10.1007/s00335-005-0050-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2005] [Accepted: 09/08/2005] [Indexed: 10/25/2022]
Abstract
Two related genes with potentially similar functions, one on the Y chromosome and one on the X chromosome, were examined to determine if they evolved differently because of their chromosomal positions. Six hundred fifty-seven base pairs of coding sequence of Jarid1d (Smcy) on the Y chromosome and Jarid1c (Smcx) on the X chromosome were sequenced in 13 rodent taxa. An analysis of replacement and silent substitutions, using a counting method designed for samples with small evolutionary distances, showed a significant difference between the two genes. The different patterns of replacement and silent substitutions within Jarid1d and Jarid1c may be a result of evolutionary mechanisms that are particularly strong on the Y chromosome because of its unique properties. These findings are similar to results of previous studies of Y chromosomal genes in these and other mammalian taxa, suggesting that genes on the mammalian Y evolve in a chromosome-specific manner.
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Affiliation(s)
- Sara A Sandstedt
- Department of Ecology and Evolutionary Biology, and Museum of Zoology, University of Michigan, Ann Arbor, Michigan 48109, USA.
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Berlin S, Ellegren H. Fast accumulation of nonsynonymous mutations on the female-specific W chromosome in birds. J Mol Evol 2005; 62:66-72. [PMID: 16320115 DOI: 10.1007/s00239-005-0067-6] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2005] [Accepted: 07/31/2005] [Indexed: 11/26/2022]
Abstract
Following cessation of recombination during sex chromosome evolution, the nonrecombining sex chromosome is affected by a number of degenerative forces, possibly resulting in the fixation of deleterious mutations. This might take place because of weak selection against recessive or partly recessive deleterious mutations due to permanent heterozygosity of nonrecombining chromosomes. Furthermore, population genetic processes, such as selective sweeps, background selection, and Muller's ratchet, result in a reduction in Ne, which increase the likelihood of fixation of deleterious mutations. Theory thus predicts that nonrecombining genes should show increased levels of nonsynonymous (dN) to synonymous substitutions (dS). We tested this in an avian system by estimating the ratio between dN and dS in six gametologous gene pairs located on the Z chromosome and the nonrecombining, female-specific W chromosome. In comparisons, we found a significantly higher dN/dS ratio for the W-linked than the Z-linked copy in three of the investigated genes. In a concatenated alignment of all six genes, the dN/dS ratio was six times higher for W-linked than Z-linked genes. By using human and mouse as outgroup in maximum likelihood analyses, W-linked genes were found to evolve differently compared with their Z-linked gametologues and outgroup sequences. This seems not to be a consequence of functional diversification because d(N)/d(S) ratios between gametologous gene copies were consistently low. We conclude that deleterious mutations are accumulating at a high rate on the avian W chromosome, probably as a result of the lack of recombination in this female-specific chromosome.
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Affiliation(s)
- Sofia Berlin
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvagen 18 D, 752 36, Uppsala, Sweden.
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Bachtrog D. Sex chromosome evolution: molecular aspects of Y-chromosome degeneration in Drosophila. Genome Res 2005; 15:1393-401. [PMID: 16169921 PMCID: PMC1240082 DOI: 10.1101/gr.3543605] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Ancient Y-chromosomes of various organisms contain few active genes and an abundance of repetitive DNA. The neo-Y chromosome of Drosophila miranda is in transition from an ordinary autosome to a genetically inert Y-chromosome, while its homolog, the neo-X chromosome, is evolving partial dosage compensation. Here, I compare four large genomic regions located on the neo-sex chromosomes that contain a total of 12 homologous genes. In addition, I investigate the partial coding sequence for 56 more homologous gene pairs from the neo-sex chromosomes. Little modification has occurred on the neo-X chromosome, and genes are highly constrained at the protein level. In contrast, a diverse array of molecular changes is contributing to the observed degeneration of the neo-Y chromosome. In particular, the four large regions surveyed on the neo-Y chromosome harbor several transposable element insertions, large deletions, and a large structural rearrangement. About one-third of all neo-Y-linked genes are nonfunctional, containing either premature stop codons and/or frameshift mutations. Intact genes on the neo-Y are accumulating amino acid and unpreferred codon changes. In addition, both 5'- and 3'-flanking regions of genes and intron sequences are less constrained on the neo-Y relative to the neo-X. Despite heterogeneity in levels of dosage compensation along the neo-X chromosome of D. miranda, the neo-Y chromosome shows surprisingly uniform signs of degeneration.
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Affiliation(s)
- Doris Bachtrog
- Department of Ecology, Behavior and Evolution, University of California, San Diego, La Jolla, California 92093, USA.
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Abstract
Y chromosomes are genetically degenerate in most organisms studied. The loss of genes from Y chromosomes is thought to be due to the inefficiency of purifying selection in nonrecombining regions, which leads to the accumulation of deleterious mutations via the processes of hitchhiking, background selection, and Muller's ratchet. As the severity of these processes depends on the number of functional genes linked together on the nonrecombining Y, it is not clear whether these processes are still at work on the old, gene-poor mammalian Y chromosomes. If purifying selection is indeed less efficient in the Y-linked, compared to the X-linked genes, deleterious nonsynonymous substitutions are expected to accumulate faster on the Y chromosome. However, positive selection on Y-linked genes could also increase the rate of amino acid-changing substitutions. Thus, the previous reports of an elevated nonsynonymous substitution rate in Y-linked genes are still open to interpretation. Here, we report evidence for positive selection in two out of three studied mammalian Y-linked genes, suggesting that adaptive Darwinian evolution may be common on mammalian Y chromosomes. Taking positive selection into account, we demonstrate that purifying selection is less efficient in mammalian Y-linked genes compared to their X-linked homologues, suggesting that these genes continue to degenerate.
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Affiliation(s)
- Dave T Gerrard
- School of Biosciences, The University of Birmingham, Edgbaston, Birmingham, United Kingdom
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Abstract
The human Y chromosome is running out of time. In the last 300 million years, it has lost 1393 of its original 1438 genes, and at this rate it will lose the last 45 in a mere 10 million years. But there has been a proposal that perhaps rescue is at hand in the form of recently discovered gene conversion within palindromes. However, I argue here that although conversion will increase the frequency of variation of the Y (particularly amplification) between Y chromosomes in a population, it will not lead to a drive towards a more functional Y. The forces of evolution have made the Y a genetically isolated, non-recombining entity, vulnerable to genetic drift and selection for favourable new variants sharing the Y with damaging mutations. Perhaps it will even speed up the decline of the Y chromosome and the onset of a new round of sex-chromosome differentiation. The struggle to preserve males may perhaps lead to hominid speciation.
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