TY - JOUR AB - Since the commercialization of brine shrimp (genus Artemia) in the 1950s, this lineage, and in particular the model species Artemia franciscana, has been the subject of extensive research. However, our understanding of the genetic mechanisms underlying various aspects of their reproductive biology, including sex determination, is still lacking. This is partly due to the scarcity of genomic resources for Artemia species and crustaceans in general. Here, we present a chromosome-level genome assembly of A. franciscana (Kellogg 1906), from the Great Salt Lake, United States. The genome is 1 GB, and the majority of the genome (81%) is scaffolded into 21 linkage groups using a previously published high-density linkage map. We performed coverage and FST analyses using male and female genomic and transcriptomic reads to quantify the extent of differentiation between the Z and W chromosomes. Additionally, we quantified the expression levels in male and female heads and gonads and found further evidence for dosage compensation in this species. AU - Bett, Vincent K AU - Macon, Ariana AU - Vicoso, Beatriz AU - Elkrewi, Marwan N ID - 15009 IS - 1 JF - Genome Biology and Evolution TI - Chromosome-level assembly of Artemia franciscana sheds light on sex chromosome differentiation VL - 16 ER - TY - JOUR AB - Differentiated X chromosomes are expected to have higher rates of adaptive divergence than autosomes, if new beneficial mutations are recessive (the “faster-X effect”), largely because these mutations are immediately exposed to selection in males. The evolution of X chromosomes after they stop recombining in males, but before they become hemizygous, has not been well explored theoretically. We use the diffusion approximation to infer substitution rates of beneficial and deleterious mutations under such a scenario. Our results show that selection is less efficient on diploid X loci than on autosomal and hemizygous X loci under a wide range of parameters. This “slower-X” effect is stronger for genes affecting primarily (or only) male fitness, and for sexually antagonistic genes. These unusual dynamics suggest that some of the peculiar features of X chromosomes, such as the differential accumulation of genes with sex-specific functions, may start arising earlier than previously appreciated. AU - Mrnjavac, Andrea AU - Khudiakova, Kseniia AU - Barton, Nicholas H AU - Vicoso, Beatriz ID - 12521 IS - 1 JF - Evolution Letters KW - Genetics KW - Ecology KW - Evolution KW - Behavior and Systematics SN - 2056-3744 TI - Slower-X: Reduced efficiency of selection in the early stages of X chromosome evolution VL - 7 ER - TY - JOUR AB - Sex chromosomes have evolved independently multiple times, but why some are conserved for more than 100 million years whereas others turnover rapidly remains an open question. Here, we examine the homology of sex chromosomes across nine orders of insects, plus the outgroup springtails. We find that the X chromosome is likely homologous across insects and springtails; the only exception is in the Lepidoptera, which has lost the X and now has a ZZ/ZW sex-chromosome system. These results suggest the ancestral insect X chromosome has persisted for more than 450 million years—the oldest known sex chromosome to date. Further, we propose that the shrinking of gene content the dipteran X chromosome has allowed for a burst of sex-chromosome turnover that is absent from other speciose insect orders. AU - Toups, Melissa A AU - Vicoso, Beatriz ID - 14604 IS - 11 JF - Evolution TI - The X chromosome of insects likely predates the origin of class Insecta VL - 77 ER - TY - GEN AB - Sex chromosomes have evolved independently multiple times, but why some are conserved for more than 100 million years whereas others turnover rapidly remains an open question. Here, we examine the homology of sex chromosomes across nine orders of insects, plus the outgroup springtails. We find that the X chromosome is likely homologous across insects and springtails; the only exception is in the Lepidoptera, which has lost the X and now has a ZZ/ZW sex chromosome system. These results suggest the ancestral insect X chromosome has persisted for more than 450 million years – the oldest known sex chromosome to date. Further, we propose that the shrinking of gene content of the Dipteran X chromosome has allowed for a burst of sex-chromosome turnover that is absent from other speciose insect orders. AU - Toups, Melissa A AU - Vicoso, Beatriz ID - 14616 TI - The X chromosome of insects likely predates the origin of Class Insecta ER - TY - GEN AB - Sex chromosomes have evolved independently multiple times, but why some are conserved for more than 100 million years whereas others turnover rapidly remains an open question. Here, we examine the homology of sex chromosomes across nine orders of insects, plus the outgroup springtails. We find that the X chromosome is likely homologous across insects and springtails; the only exception is in the Lepidoptera, which has lost the X and now has a ZZ/ZW sex chromosome system. These results suggest the ancestral insect X chromosome has persisted for more than 450 million years – the oldest known sex chromosome to date. Further, we propose that the shrinking of gene content of the Dipteran X chromosome has allowed for a burst of sex-chromosome turnover that is absent from other speciose insect orders. AU - Toups, Melissa A AU - Vicoso, Beatriz ID - 14617 TI - The X chromosome of insects likely predates the origin of Class Insecta ER - TY - JOUR AB - The regulatory architecture of gene expression is known to differ substantially between sexes in Drosophila, but most studies performed so far used whole-body data and only single crosses, which may have limited their scope to detect patterns that are robust across tissues and biological replicates. Here, we use allele-specific gene expression of parental and reciprocal hybrid crosses between 6 Drosophila melanogaster inbred lines to quantify cis- and trans-regulatory variation in heads and gonads of both sexes separately across 3 replicate crosses. Our results suggest that female and male heads, as well as ovaries, have a similar regulatory architecture. On the other hand, testes display more and substantially different cis-regulatory effects, suggesting that sex differences in the regulatory architecture that have been previously observed may largely derive from testis-specific effects. We also examine the difference in cis-regulatory variation of genes across different levels of sex bias in gonads and heads. Consistent with the idea that intersex correlations constrain expression and can lead to sexual antagonism, we find more cis variation in unbiased and moderately biased genes in heads. In ovaries, reduced cis variation is observed for male-biased genes, suggesting that cis variants acting on these genes in males do not lead to changes in ovary expression. Finally, we examine the dominance patterns of gene expression and find that sex- and tissue-specific patterns of inheritance as well as trans-regulatory variation are highly variable across biological crosses, although these were performed in highly controlled experimental conditions. This highlights the importance of using various genetic backgrounds to infer generalizable patterns. AU - Puixeu Sala, Gemma AU - Macon, Ariana AU - Vicoso, Beatriz ID - 14077 IS - 8 JF - G3: Genes, Genomes, Genetics KW - Genetics (clinical) KW - Genetics KW - Molecular Biology SN - 2160-1836 TI - Sex-specific estimation of cis and trans regulation of gene expression in heads and gonads of Drosophila melanogaster VL - 13 ER - TY - JOUR AB - Many insects carry an ancient X chromosome - the Drosophila Muller element F - that likely predates their origin. Interestingly, the X has undergone turnover in multiple fly species (Diptera) after being conserved for more than 450 MY. The long evolutionary distance between Diptera and other sequenced insect clades makes it difficult to infer what could have contributed to this sudden increase in rate of turnover. Here, we produce the first genome and transcriptome of a long overlooked sister-order to Diptera: Mecoptera. We compare the scorpionfly Panorpa cognata X-chromosome gene content, expression, and structure, to that of several dipteran species as well as more distantly-related insect orders (Orthoptera and Blattodea). We find high conservation of gene content between the mecopteran X and the dipteran Muller F element, as well as several shared biological features, such as the presence of dosage compensation and a low amount of genetic diversity, consistent with a low recombination rate. However, the two homologous X chromosomes differ strikingly in their size and number of genes they carry. Our results therefore support a common ancestry of the mecopteran and ancestral dipteran X chromosomes, and suggest that Muller element F shrank in size and gene content after the split of Diptera and Mecoptera, which may have contributed to its turnover in dipteran insects. AU - Lasne, Clementine AU - Elkrewi, Marwan N AU - Toups, Melissa A AU - Layana Franco, Lorena Alexandra AU - Macon, Ariana AU - Vicoso, Beatriz ID - 14613 IS - 12 JF - Molecular Biology and Evolution KW - Genetics KW - Molecular Biology KW - Ecology KW - Evolution KW - Behavior and Systematics SN - 0737-4038 TI - The scorpionfly (Panorpa cognata) genome highlights conserved and derived features of the peculiar dipteran X chromosome VL - 40 ER - TY - JOUR AB - The t-haplotype of mice is a classical model for autosomal transmission distortion. A largely non-recombining variant of the proximal region of chromosome 17, it is transmitted to more than 90% of the progeny of heterozygous males through the disabling of sperm carrying a standard chromosome. While extensive genetic and functional work has shed light on individual genes involved in drive, much less is known about the evolution and function of the rest of its hundreds of genes. Here, we characterize the sequence and expression of dozens of t-specific transcripts and of their chromosome 17 homologues. Many genes showed reduced expression of the t-allele, but an equal number of genes showed increased expression of their t-copy, consistent with increased activity or a newly evolved function. Genes on the t-haplotype had a significantly higher non-synonymous substitution rate than their homologues on the standard chromosome, with several genes harbouring dN/dS ratios above 1. Finally, the t-haplotype has acquired at least two genes from other chromosomes, which show high and tissue-specific expression. These results provide a first overview of the gene content of this selfish element, and support a more dynamic evolutionary scenario than expected of a large genomic region with almost no recombination. AU - Kelemen, Réka K AU - Elkrewi, Marwan N AU - Lindholm, Anna K. AU - Vicoso, Beatriz ID - 10767 IS - 1968 JF - Proceedings of the Royal Society B: Biological Sciences TI - Novel patterns of expression and recruitment of new genes on the t-haplotype, a mouse selfish chromosome VL - 289 ER - TY - JOUR AB - Polyploidization may precipitate dramatic changes to the genome, including chromosome rearrangements, gene loss, and changes in gene expression. In dioecious plants, the sex-determining mechanism may also be disrupted by polyploidization, with the potential evolution of hermaphroditism. However, while dioecy appears to have persisted through a ploidy transition in some species, it is unknown whether the newly formed polyploid maintained its sex-determining system uninterrupted, or whether dioecy re-evolved after a period of hermaphroditism. Here, we develop a bioinformatic pipeline using RNA-sequencing data from natural populations to demonstrate that the allopolyploid plant Mercurialis canariensis directly inherited its sex-determining region from one of its diploid progenitor species, M. annua, and likely remained dioecious through the transition. The sex-determining region of M. canariensis is smaller than that of its diploid progenitor, suggesting that the non-recombining region of M. annua expanded subsequent to the polyploid origin of M. canariensis. Homeologous pairs show partial sexual subfunctionalization. We discuss the possibility that gene duplicates created by polyploidization might contribute to resolving sexual antagonism. AU - Toups, Melissa A AU - Vicoso, Beatriz AU - Pannell, John R. ID - 11703 IS - 7 JF - PLoS Genetics TI - Dioecy and chromosomal sex determination are maintained through allopolyploid speciation in the plant genus Mercurialis VL - 18 ER - TY - JOUR AB - Eurasian brine shrimp (genus Artemia) have closely related sexual and asexual lineages of parthenogenetic females, which produce rare males at low frequencies. Although they are known to have ZW chromosomes, these are not well characterized, and it is unclear whether they are shared across the clade. Furthermore, the underlying genetic architecture of the transmission of asexuality, which can occur when rare males mate with closely related sexual females, is not well understood. We produced a chromosome-level assembly for the sexual Eurasian species Artemia sinica and characterized in detail the pair of sex chromosomes of this species. We combined this new assembly with short-read genomic data for the sexual species Artemia sp. Kazakhstan and several asexual lineages of Artemia parthenogenetica, allowing us to perform an in-depth characterization of sex-chromosome evolution across the genus. We identified a small differentiated region of the ZW pair that is shared by all sexual and asexual lineages, supporting the shared ancestry of the sex chromosomes. We also inferred that recombination suppression has spread to larger sections of the chromosome independently in the American and Eurasian lineages. Finally, we took advantage of a rare male, which we backcrossed to sexual females, to explore the genetic basis of asexuality. Our results suggest that parthenogenesis is likely partly controlled by a locus on the Z chromosome, highlighting the interplay between sex determination and asexuality. AU - Elkrewi, Marwan N AU - Khauratovich, Uladzislava AU - Toups, Melissa A AU - Bett, Vincent K AU - Mrnjavac, Andrea AU - Macon, Ariana AU - Fraisse, Christelle AU - Sax, Luca AU - Huylmans, Ann K AU - Hontoria, Francisco AU - Vicoso, Beatriz ID - 12248 IS - 2 JF - Genetics KW - Genetics SN - 1943-2631 TI - ZW sex-chromosome evolution and contagious parthenogenesis in Artemia brine shrimp VL - 222 ER - TY - JOUR AB - About eight million animal species are estimated to live on Earth, and all except those belonging to one subphylum are invertebrates. Invertebrates are incredibly diverse in their morphologies, life histories, and in the range of the ecological niches that they occupy. A great variety of modes of reproduction and sex determination systems is also observed among them, and their mosaic-distribution across the phylogeny shows that transitions between them occur frequently and rapidly. Genetic conflict in its various forms is a long-standing theory to explain what drives those evolutionary transitions. Here, we review (1) the different modes of reproduction among invertebrate species, highlighting sexual reproduction as the probable ancestral state; (2) the paradoxical diversity of sex determination systems; (3) the different types of genetic conflicts that could drive the evolution of such different systems. AU - Picard, Marion A L AU - Vicoso, Beatriz AU - Bertrand, Stéphanie AU - Escriva, Hector ID - 9908 IS - 8 JF - Genes TI - Diversity of modes of reproduction and sex determination systems in invertebrates, and the putative contribution of genetic conflict VL - 12 ER - TY - JOUR AB - Schistosomes, the human parasites responsible for snail fever, are female-heterogametic. Different parts of their ZW sex chromosomes have stopped recombining in distinct lineages, creating “evolutionary strata” of various ages. Although the Z-chromosome is well characterized at the genomic and molecular level, the W-chromosome has remained largely unstudied from an evolutionary perspective, as only a few W-linked genes have been detected outside of the model species Schistosoma mansoni. Here, we characterize the gene content and evolution of the W-chromosomes of S. mansoni and of the divergent species S. japonicum. We use a combined RNA/DNA k-mer based pipeline to assemble around 100 candidate W-specific transcripts in each of the species. About half of them map to known protein coding genes, the majority homologous to S. mansoni Z-linked genes. We perform an extended analysis of the evolutionary strata present in the two species (including characterizing a previously undetected young stratum in S. japonicum) to infer patterns of sequence and expression evolution of W-linked genes at different time points after recombination was lost. W-linked genes show evidence of degeneration, including high rates of protein evolution and reduced expression. Most are found in young lineage-specific strata, with only a few high expression ancestral W-genes remaining, consistent with the progressive erosion of nonrecombining regions. Among these, the splicing factor u2af2 stands out as a promising candidate for primary sex determination, opening new avenues for understanding the molecular basis of the reproductive biology of this group. AU - Elkrewi, Marwan N AU - Moldovan, Mikhail A. AU - Picard, Marion A L AU - Vicoso, Beatriz ID - 10167 JF - Molecular Biology and Evolution KW - sex chromosomes KW - evolutionary strata KW - W-linked gene KW - sex determining gene KW - schistosome parasites SN - 0737-4038 TI - Schistosome W-Linked genes inform temporal dynamics of sex chromosome evolution and suggest candidate for sex determination ER - TY - JOUR AB - While sexual reproduction is widespread among many taxa, asexual lineages have repeatedly evolved from sexual ancestors. Despite extensive research on the evolution of sex, it is still unclear whether this switch represents a major transition requiring major molecular reorganization, and how convergent the changes involved are. In this study, we investigated the phylogenetic relationship and patterns of gene expression of sexual and asexual lineages of Eurasian Artemia brine shrimp, to assess how gene expression patterns are affected by the transition to asexuality. We find only a few genes that are consistently associated with the evolution of asexuality, suggesting that this shift may not require an extensive overhauling of the meiotic machinery. While genes with sex-biased expression have high rates of expression divergence within Eurasian Artemia, neither female- nor male-biased genes appear to show unusual evolutionary patterns after sexuality is lost, contrary to theoretical expectations. AU - Huylmans, Ann K AU - Macon, Ariana AU - Hontoria, Francisco AU - Vicoso, Beatriz ID - 10166 IS - 1959 JF - Proceedings of the Royal Society B: Biological Sciences KW - asexual reproduction KW - parthenogenesis KW - sex-biased genes KW - sexual conflict KW - automixis KW - crustaceans SN - 0962-8452 TI - Transitions to asexuality and evolution of gene expression in Artemia brine shrimp VL - 288 ER - TY - DATA AU - Vicoso, Beatriz ID - 9949 TI - Data from Hyulmans et al 2021, "Transitions to asexuality and evolution of gene expression in Artemia brine shrimp" ER - TY - JOUR AB - Sewall Wright developed FST for describing population differentiation and it has since been extended to many novel applications, including the detection of homomorphic sex chromosomes. However, there has been confusion regarding the expected estimate of FST for a fixed difference between the X‐ and Y‐chromosome when comparing males and females. Here, we attempt to resolve this confusion by contrasting two common FST estimators and explain why they yield different estimates when applied to the case of sex chromosomes. We show that this difference is true for many allele frequencies, but the situation characterized by fixed differences between the X‐ and Y‐chromosome is among the most extreme. To avoid additional confusion, we recommend that all authors using FST clearly state which estimator of FST their work uses. AU - Gammerdinger, William J AU - Toups, Melissa A AU - Vicoso, Beatriz ID - 8099 IS - 6 JF - Molecular Ecology Resources SN - 1755-098X TI - Disagreement in FST estimators: A case study from sex chromosomes VL - 20 ER - TY - JOUR AB - Differentiated sex chromosomes are accompanied by a difference in gene dose between X/Z-specific and autosomal genes. At the transcriptomic level, these sex-linked genes can lead to expression imbalance, or gene dosage can be compensated by epigenetic mechanisms and results into expression level equalization. Schistosoma mansoni has been previously described as a ZW species (i.e., female heterogamety, in opposition to XY male heterogametic species) with a partial dosage compensation, but underlying mechanisms are still unexplored. Here, we combine transcriptomic (RNA-Seq) and epigenetic data (ChIP-Seq against H3K4me3, H3K27me3,andH4K20me1histonemarks) in free larval cercariae and intravertebrate parasitic stages. For the first time, we describe differences in dosage compensation status in ZW females, depending on the parasitic status: free cercariae display global dosage compensation, whereas intravertebrate stages show a partial dosage compensation. We also highlight regional differences of gene expression along the Z chromosome in cercariae, but not in the intravertebrate stages. Finally, we feature a consistent permissive chromatin landscape of the Z chromosome in both sexes and stages. We argue that dosage compensation in schistosomes is characterized by chromatin remodeling mechanisms in the Z-specific region. AU - Picard, Marion A L AU - Vicoso, Beatriz AU - Roquis, David AU - Bulla, Ingo AU - Augusto, Ronaldo C. AU - Arancibia, Nathalie AU - Grunau, Christoph AU - Boissier, Jérôme AU - Cosseau, Céline ID - 6755 IS - 7 JF - Genome biology and evolution TI - Dosage compensation throughout the Schistosoma mansoni lifecycle: Specific chromatin landscape of the Z chromosome VL - 11 ER - TY - JOUR AB - Prevailing models of sex-chromosome evolution were largely inspired by the stable and highly differentiated XY pairs of model organisms, such as those of mammals and flies. Recent work has uncovered an incredible diversity of sex-determining systems, bringing some of the assumptions of these traditional models into question. One particular question that has arisen is what drives some sex chromosomes to be maintained over millions of years and differentiate fully, while others are replaced by new sex-determining chromosomes before differentiation has occurred. Here, I review recent data on the variability of sex-determining genes and sex chromosomes in different non-model vertebrates and invertebrates, and discuss some theoretical models that have been put forward to account for this diversity. AU - Vicoso, Beatriz ID - 7146 IS - 12 JF - Nature Ecology & Evolution SN - 2397-334X TI - Molecular and evolutionary dynamics of animal sex-chromosome turnover VL - 3 ER - TY - JOUR AB - We read with great interest the recent work in PNAS by Bergero et al. (1) describing differences in male and female recombination patterns on the guppy (Poecilia reticulata) sex chromosome. We fully agree that recombination in males is largely confined to the ends of the sex chromosome. Bergero et al. interpret these results to suggest that our previous findings of population-level variation in the degree of sex chromosome differentiation in this species (2) are incorrect. However, we suggest that their results are entirely consistent with our previous report, and that their interpretation presents a false controversy. AU - Wright, Alison E. AU - Darolti, Iulia AU - Bloch, Natasha I. AU - Oostra, Vicencio AU - Sandkam, Benjamin A. AU - Buechel, Séverine D. AU - Kolm, Niclas AU - Breden, Felix AU - Vicoso, Beatriz AU - Mank, Judith E. ID - 6621 IS - 26 JF - Proceedings of the National Academy of Sciences of the United States of America TI - On the power to detect rare recombination events VL - 116 ER - TY - JOUR AB - Males and females of Artemia franciscana, a crustacean commonly used in the aquarium trade, are highly dimorphic. Sex is determined by a pair of ZW chromosomes, but the nature and extent of differentiation of these chromosomes is unknown. Here, we characterize the Z chromosome by detecting genomic regions that show lower genomic coverage in female than in male samples, and regions that harbor an excess of female-specific SNPs. We detect many Z-specific genes, which no longer have homologs on the W, but also Z-linked genes that appear to have diverged very recently from their existing W-linked homolog. We assess patterns of male and female expression in two tissues with extensive morphological dimorphism, gonads, and heads. In agreement with their morphology, sex-biased expression is common in both tissues. Interestingly, the Z chromosome is not enriched for sex-biased genes, and seems to in fact have a mechanism of dosage compensation that leads to equal expression in males and in females. Both of these patterns are contrary to most ZW systems studied so far, making A. franciscana an excellent model for investigating the interplay between the evolution of sexual dimorphism and dosage compensation, as well as Z chromosome evolution in general. AU - Huylmans, Ann K AU - Toups, Melissa A AU - Macon, Ariana AU - Gammerdinger, William J AU - Vicoso, Beatriz ID - 6418 IS - 4 JF - Genome biology and evolution TI - Sex-biased gene expression and dosage compensation on the Artemia franciscana Z-chromosome VL - 11 ER - TY - DATA AU - Vicoso, Beatriz ID - 6060 TI - Supplementary data for "Sex-biased gene expression and dosage compensation on the Artemia franciscana Z-chromosome" (Huylman, Toups et al., 2019). ER - TY - JOUR AB - Pleiotropy is the well-established idea that a single mutation affects multiple phenotypes. If a mutation has opposite effects on fitness when expressed in different contexts, then genetic conflict arises. Pleiotropic conflict is expected to reduce the efficacy of selection by limiting the fixation of beneficial mutations through adaptation, and the removal of deleterious mutations through purifying selection. Although this has been widely discussed, in particular in the context of a putative “gender load,” it has yet to be systematically quantified. In this work, we empirically estimate to which extent different pleiotropic regimes impede the efficacy of selection in Drosophila melanogaster. We use whole-genome polymorphism data from a single African population and divergence data from D. simulans to estimate the fraction of adaptive fixations (α), the rate of adaptation (ωA), and the direction of selection (DoS). After controlling for confounding covariates, we find that the different pleiotropic regimes have a relatively small, but significant, effect on selection efficacy. Specifically, our results suggest that pleiotropic sexual antagonism may restrict the efficacy of selection, but that this conflict can be resolved by limiting the expression of genes to the sex where they are beneficial. Intermediate levels of pleiotropy across tissues and life stages can also lead to maladaptation in D. melanogaster, due to inefficient purifying selection combined with low frequency of mutations that confer a selective advantage. Thus, our study highlights the need to consider the efficacy of selection in the context of antagonistic pleiotropy, and of genetic conflict in general. AU - Fraisse, Christelle AU - Puixeu Sala, Gemma AU - Vicoso, Beatriz ID - 6089 IS - 3 JF - Molecular biology and evolution SN - 0737-4038 TI - Pleiotropy modulates the efficacy of selection in drosophila melanogaster VL - 36 ER - TY - JOUR AB - XY systems usually show chromosome-wide compensation of X-linked genes, while in many ZW systems, compensation is restricted to a minority of dosage-sensitive genes. Why such differences arose is still unclear. Here, we combine comparative genomics, transcriptomics and proteomics to obtain a complete overview of the evolution of gene dosage on the Z-chromosome of Schistosoma parasites. We compare the Z-chromosome gene content of African (Schistosoma mansoni and S. haematobium) and Asian (S. japonicum) schistosomes and describe lineage-specific evolutionary strata. We use these to assess gene expression evolution following sex-linkage. The resulting patterns suggest a reduction in expression of Z-linked genes in females, combined with upregulation of the Z in both sexes, in line with the first step of Ohno’s classic model of dosage compensation evolution. Quantitative proteomics suggest that post-transcriptional mechanisms do not play a major role in balancing the expression of Z-linked genes. AU - Picard, Marion A AU - Cosseau, Celine AU - Ferré, Sabrina AU - Quack, Thomas AU - Grevelding, Christoph AU - Couté, Yohann AU - Vicoso, Beatriz ID - 131 JF - eLife TI - Evolution of gene dosage on the Z-chromosome of schistosome parasites VL - 7 ER - TY - DATA AB - Input files and scripts from "Evolution of gene dosage on the Z-chromosome of schistosome parasites" by Picard M.A.L., et al (2018). AU - Vicoso, Beatriz ID - 5586 KW - schistosoma KW - Z-chromosome KW - gene expression TI - Input files and scripts from "Evolution of gene dosage on the Z-chromosome of schistosome parasites" by Picard M.A.L., et al (2018) ER - TY - JOUR AB - The t-haplotype, a mouse meiotic driver found on chromosome 17, has been a model for autosomal segregation distortion for close to a century, but several questions remain regarding its biology and evolutionary history. A recently published set of population genomics resources for wild mice includes several individuals heterozygous for the t-haplotype, which we use to characterize this selfish element at the genomic and transcriptomic level. Our results show that large sections of the t-haplotype have been replaced by standard homologous sequences, possibly due to occasional events of recombination, and that this complicates the inference of its history. As expected for a long genomic segment of very low recombination, the t-haplotype carries an excess of fixed nonsynonymous mutations compared to the standard chromosome. This excess is stronger for regions that have not undergone recent recombination, suggesting that occasional gene flow between the t and the standard chromosome may provide a mechanism to regenerate coding sequences that have accumulated deleterious mutations. Finally, we find that t-complex genes with altered expression largely overlap with deleted or amplified regions, and that carrying a t-haplotype alters the testis expression of genes outside of the t-complex, providing new leads into the pathways involved in the biology of this segregation distorter. AU - Kelemen, Réka K AU - Vicoso, Beatriz ID - 542 IS - 1 JF - Genetics TI - Complex history and differentiation patterns of the t-haplotype, a mouse meiotic driver VL - 208 ER - TY - JOUR AB - Sex chromosomes evolve once recombination is halted between a homologous pair of chromosomes. The dominant model of sex chromosome evolution posits that recombination is suppressed between emerging X and Y chromosomes in order to resolve sexual conflict. Here we test this model using whole genome and transcriptome resequencing data in the guppy, a model for sexual selection with many Y-linked colour traits. We show that although the nascent Y chromosome encompasses nearly half of the linkage group, there has been no perceptible degradation of Y chromosome gene content or activity. Using replicate wild populations with differing levels of sexually antagonistic selection for colour, we also show that sexual selection leads to greater expansion of the non-recombining region and increased Y chromosome divergence. These results provide empirical support for longstanding models of sex chromosome catalysis, and suggest an important role for sexual selection and sexual conflict in genome evolution. AU - Wright, Alison AU - Darolti, Iulia AU - Bloch, Natasha AU - Oostra, Vicencio AU - Sandkam, Benjamin AU - Buechel, Séverine AU - Kolm, Niclas AU - Breden, Felix AU - Vicoso, Beatriz AU - Mank, Judith ID - 1085 JF - Nature Communications SN - 20411723 TI - Convergent recombination suppression suggests role of sexual selection in guppy sex chromosome formation VL - 8 ER - TY - JOUR AB - While chromosome-wide dosage compensation of the X chromosome has been found in many species, studies in ZW clades have indicated that compensation of the Z is more localized and/or incomplete. In the ZW Lepidoptera, some species show complete compensation of the Z chromosome, while others lack full equalization, but what drives these inconsistencies is unclear. Here, we compare patterns of male and female gene expression on the Z chromosome of two closely related butterfly species, Papilio xuthus and Papilio machaon, and in multiple tissues of two moths species, Plodia interpunctella and Bombyx mori, which were previously found to differ in the extent to which they equalize Z-linked gene expression between the sexes. We find that, while some species and tissues seem to have incomplete dosage compensation, this is in fact due to the accumulation of male-biased genes and the depletion of female-biased genes on the Z chromosome. Once this is accounted for, the Z chromosome is fully compensated in all four species, through the up-regulation of Z expression in females and in some cases additional down-regulation in males. We further find that both sex-biased genes and Z-linked genes have increased rates of expression divergence in this clade, and that this can lead to fast shifts in patterns of gene expression even between closely related species. Taken together, these results show that the uneven distribution of sex-biased genes on sex chromosomes can confound conclusions about dosage compensation and that Z chromosome-wide dosage compensation is not only possible but ubiquitous among Lepidoptera. AU - Huylmans, Ann K AU - Macon, Ariana AU - Vicoso, Beatriz ID - 945 IS - 10 JF - Molecular Biology and Evolution SN - 07374038 TI - Global dosage compensation is ubiquitous in Lepidoptera, but counteracted by the masculinization of the Z chromosome VL - 34 ER - TY - JOUR AB - Moths and butterflies (Lepidoptera) usually have a pair of differentiated WZ sex chromosomes. However, in most lineages outside of the division Ditrysia, as well as in the sister order Trichoptera, females lack a W chromosome. The W is therefore thought to have been acquired secondarily. Here we compare the genomes of three Lepidoptera species (one Dytrisia and two non-Dytrisia) to test three models accounting for the origin of the W: (1) a Z-autosome fusion; (2) a sex chromosome turnover; and (3) a non-canonical mechanism (e.g., through the recruitment of a B chromosome). We show that the gene content of the Z is highly conserved across Lepidoptera (rejecting a sex chromosome turnover) and that very few genes moved onto the Z in the common ancestor of the Ditrysia (arguing against a Z-autosome fusion). Our comparative genomics analysis therefore supports the secondary acquisition of the Lepidoptera W by a non-canonical mechanism, and it confirms the extreme stability of well-differentiated sex chromosomes. AU - Fraisse, Christelle AU - Picard, Marion A AU - Vicoso, Beatriz ID - 614 IS - 1 JF - Nature Communications SN - 20411723 TI - The deep conservation of the Lepidoptera Z chromosome suggests a non canonical origin of the W VL - 8 ER - TY - DATA AB - This folder contains all the data used in each of the main figures of "The genomic characterization of the t-haplotype, a mouse meiotic driver, highlights its complex history and specialized biology" (Kelemen, R., Vicoso, B.), as well as in the supplementary figures. AU - Vicoso, Beatriz ID - 5571 TI - Data for "The genomic characterization of the t-haplotype, a mouse meiotic driver, highlights its complex history and specialized biology" ER - TY - DATA AB - Code described in the Supplementary Methods of "The genomic characterization of the t-haplotype, a mouse meiotic driver, highlights its complex history and specialized biology" (Kelemen, R., Vicoso, B.) AU - Vicoso, Beatriz ID - 5572 TI - Code for "The genomic characterization of the t-haplotype, a mouse meiotic driver, highlights its complex history and specialized biology" ER - TY - JOUR AB - Insects of the order Hemiptera (true bugs) use a wide range of mechanisms of sex determination, including genetic sex determination, paternal genome elimination, and haplodiploidy. Genetic sex determination, the prevalent mode, is generally controlled by a pair of XY sex chromosomes or by an XX/X0 system, but different configurations that include additional sex chromosomes are also present. Although this diversity of sex determining systems has been extensively studied at the cytogenetic level, only the X chromosome of the model pea aphid Acyrthosiphon pisum has been analyzed at the genomic level, and little is known about X chromosome biology in the rest of the order. In this study, we take advantage of published DNA- and RNA-seq data from three additional Hemiptera species to perform a comparative analysis of the gene content and expression of the X chromosome throughout this clade. We find that, despite showing evidence of dosage compensation, the X chromosomes of these species show female-biased expression, and a deficit of male-biased genes, in direct contrast to the pea aphid X. We further detect an excess of shared gene content between these very distant species, suggesting that despite the diversity of sex determining systems, the same chromosomal element is used as the X throughout a large portion of the order. AU - Pal, Arka AU - Vicoso, Beatriz ID - 1513 IS - 12 JF - Genome Biology and Evolution TI - The X chromosome of hemipteran insects: Conservation, dosage compensation and sex-biased expression VL - 7 ER - TY - JOUR AB - Contrary to the pattern seen in mammalian sex chromosomes, where most Y-linked genes have X-linked homologs, the Drosophila X and Y chromosomes appear to be unrelated. Most of the Y-linked genes have autosomal paralogs, so autosome-to-Y transposition must be the main source of Drosophila Y-linked genes. Here we show how these genes were acquired. We found a previously unidentified gene (flagrante delicto Y, FDY) that originated from a recent duplication of the autosomal gene vig2 to the Y chromosome of Drosophila melanogaster. Four contiguous genes were duplicated along with vig2, but they became pseudogenes through the accumulation of deletions and transposable element insertions, whereas FDY remained functional, acquired testis-specific expression, and now accounts for ∼20% of the vig2-like mRNA in testis. FDY is absent in the closest relatives of D. melanogaster, and DNA sequence divergence indicates that the duplication to the Y chromosome occurred ∼2 million years ago. Thus, FDY provides a snapshot of the early stages of the establishment of a Y-linked gene and demonstrates how the Drosophila Y has been accumulating autosomal genes. AU - Carvalho, Antonio AU - Vicoso, Beatriz AU - Russo, Claudia AU - Swenor, Bonnielin AU - Clark, Andrew ID - 1577 IS - 40 JF - PNAS TI - Birth of a new gene on the Y chromosome of Drosophila melanogaster VL - 112 ER - TY - JOUR AB - Many species groups, including mammals and many insects, determine sex using heteromorphic sex chromosomes. Diptera flies, which include the model Drosophila melanogaster, generally have XY sex chromosomes and a conserved karyotype consisting of six chromosomal arms (five large rods and a small dot), but superficially similar karyotypes may conceal the true extent of sex chromosome variation. Here, we use whole-genome analysis in 37 fly species belonging to 22 different families of Diptera and uncover tremendous hidden diversity in sex chromosome karyotypes among flies. We identify over a dozen different sex chromosome configurations, and the small dot chromosome is repeatedly used as the sex chromosome, which presumably reflects the ancestral karyotype of higher Diptera. However, we identify species with undifferentiated sex chromosomes, others in which a different chromosome replaced the dot as a sex chromosome or in which up to three chromosomal elements became incorporated into the sex chromosomes, and others yet with female heterogamety (ZW sex chromosomes). Transcriptome analysis shows that dosage compensation has evolved multiple times in flies, consistently through up-regulation of the single X in males. However, X chromosomes generally show a deficiency of genes with male-biased expression, possibly reflecting sex-specific selective pressures. These species thus provide a rich resource to study sex chromosome biology in a comparative manner and show that similar selective forces have shaped the unique evolution of sex chromosomes in diverse fly taxa. AU - Vicoso, Beatriz AU - Bachtrog, Doris ID - 1684 IS - 4 JF - PLoS Biology TI - Numerous transitions of sex chromosomes in Diptera VL - 13 ER - TY - JOUR AB - Although transitions of sex-determination mechanisms are frequent in species with homomorphic sex chromosomes, heteromorphic sex chromosomes are thought to represent a terminal evolutionary stage owing to chromosome-specific adaptations such as dosage compensation or an accumulation of sex-specific mutations. Here we show that an autosome of Drosophila, the dot chromosome, was ancestrally a differentiated X chromosome. We analyse the whole genome of true fruitflies (Tephritidae), flesh flies (Sarcophagidae) and soldier flies (Stratiomyidae) to show that genes located on the dot chromosome of Drosophila are X-linked in outgroup species, whereas Drosophila X-linked genes are autosomal. We date this chromosomal transition to early drosophilid evolution by sequencing the genome of other Drosophilidae. Our results reveal several puzzling aspects of Drosophila dot chromosome biology to be possible remnants of its former life as a sex chromosome, such as its minor feminizing role in sex determination or its targeting by a chromosome-specific regulatory mechanism. We also show that patterns of biased gene expression of the dot chromosome during early embryogenesis, oogenesis and spermatogenesis resemble that of the current X chromosome. Thus, although sex chromosomes are not necessarily evolutionary end points and can revert back to an autosomal inheritance, the highly specialized genome architecture of this former X chromosome suggests that severe fitness costs must be overcome for such a turnover to occur. AU - Beatriz Vicoso AU - Bachtrog, Doris ID - 1991 IS - 7458 JF - Nature TI - Reversal of an ancient sex chromosome to an autosome in Drosophila VL - 499 ER - TY - JOUR AB - Sex chromosomes originate from autosomes. The accumulation of sexually antagonistic mutations on protosex chromosomes selects for a loss of recombination and sets in motion the evolutionary processes generating heteromorphic sex chromosomes. Recombination suppression and differentiation are generally viewed as the default path of sex chromosome evolution, and the occurrence of old, homomorphic sex chromosomes, such as those of ratite birds, has remained a mystery. Here, we analyze the genome and transcriptome of emu (Dromaius novaehollandiae) and confirm that most genes on the sex chromosome are shared between the Z and W. Surprisingly, however, levels of gene expression are generally sex-biased for all sex-linked genes relative to autosomes, including those in the pseudoautosomal region, and the male-bias increases after gonad formation. This expression bias suggests that the emu sex chromosomes have become masculinized, even in the absence of ZW differentiation. Thus, birds may have taken different evolutionary solutions to minimize the deleterious effects imposed by sexually antagonistic mutations: some lineages eliminate recombination along the protosex chromosomes to physically restrict sexually antagonistic alleles to one sex, whereas ratites evolved sex-biased expression to confine the product of a sexually antagonistic allele to the sex it benefits. This difference in conflict resolution may explain the preservation of recombining, homomorphic sex chromosomes in other lineages and illustrates the importance of sexually antagonistic mutations driving the evolution of sex chromosomes. AU - Beatriz Vicoso AU - Kaiser, Vera B AU - Bachtrog, Doris ID - 2074 IS - 16 JF - PNAS TI - Sex biased gene expression at homomorphic sex chromosomes in emus and its implication for sex chromosome evolution VL - 110 ER - TY - JOUR AB - Snakes exhibit genetic sex determination, with female heterogametic sex chromosomes (ZZ males, ZW females). Extensive cytogenetic work has suggested that the level of sex chromosome heteromorphism varies among species, with Boidae having entirely homomorphic sex chromosomes, Viperidae having completely heteromorphic sex chromosomes, and Colubridae showing partial differentiation. Here, we take a genomic approach to compare sex chromosome differentiation in these three snake families. We identify homomorphic sex chromosomes in boas (Boidae), but completely heteromorphic sex chromosomes in both garter snakes (Colubridae) and pygmy rattlesnake (Viperidae). Detection of W-linked gametologs enables us to establish the presence of evolutionary strata on garter and pygmy rattlesnake sex chromosomes where recombination was abolished at different time points. Sequence analysis shows that all strata are shared between pygmy rattlesnake and garter snake, i.e., recombination was abolished between the sex chromosomes before the two lineages diverged. The sex-biased transmission of the Z and its hemizygosity in females can impact patterns of molecular evolution, and we show that rates of evolution for Z-linked genes are increased relative to their pseudoautosomal homologs, both at synonymous and amino acid sites (even after controlling for mutational biases). This demonstrates that mutation rates are male-biased in snakes (male-driven evolution), but also supports faster-Z evolution due to differential selective effects on the Z. Finally, we perform a transcriptome analysis in boa and pygmy rattlesnake to establish baseline levels of sex-biased expression in homomorphic sex chromosomes, and show that heteromorphic ZW chromosomes in rattlesnakes lack chromosome-wide dosage compensation. Our study provides the first full scale overview of the evolution of snake sex chromosomes at the genomic level, thus greatly expanding our knowledge of reptilian and vertebrate sex chromosomes evolution. AU - Beatriz Vicoso AU - Emerson, Jr J. AU - Zektser, Yulia AU - Mahajan, Shivani AU - Bachtrog, Doris ID - 2076 IS - 8 JF - PLoS Biology TI - Comparative sex chromosome genomics in snakes: Differentiation evolutionary strata and lack of global dosage compensation VL - 11 ER - TY - JOUR AB - Background: Drosophila albomicans is a unique model organism for studying both sex chromosome and B chromosome evolution. A pair of its autosomes comprising roughly 40% of the whole genome has fused to the ancient X and Y chromosomes only about 0.12 million years ago, thereby creating the youngest and most gene-rich neo-sex system reported to date. This species also possesses recently derived B chromosomes that show non-Mendelian inheritance and significantly influence fertility.Methods: We sequenced male flies with B chromosomes at 124.5-fold genome coverage using next-generation sequencing. To characterize neo-Y specific changes and B chromosome sequences, we also sequenced inbred female flies derived from the same strain but without B's at 28.5-fold.Results: We assembled a female genome and placed 53% of the sequence and 85% of the annotated proteins into specific chromosomes, by comparison with the 12 Drosophila genomes. Despite its very recent origin, the non-recombining neo-Y chromosome shows various signs of degeneration, including a significant enrichment of non-functional genes compared to the neo-X, and an excess of tandem duplications relative to other chromosomes. We also characterized a B-chromosome linked scaffold that contains an actively transcribed unit and shows sequence similarity to the subcentromeric regions of both the ancient X and the neo-X chromosome.Conclusions: Our results provide novel insights into the very early stages of sex chromosome evolution and B chromosome origination, and suggest an unprecedented connection between the births of these two systems in D. albomicans. AU - Zhou, Qi AU - Zhu, Hongmei AU - Huang, Quanfei AU - Zhao, Li AU - Zhang, Guo J AU - Roy, Scott W AU - Beatriz Vicoso AU - Xuan, Zhaolin AU - Ruan, Jue AU - Zhang, Yue AU - Zhao, Ruoping AU - Ye, Chen AU - Zhang, Xiuqing AU - Wang, Jùn AU - Wang, Wen AU - Bachtrog, Doris ID - 2073 IS - 1 JF - BMC Genomics TI - Deciphering neo-sex and B chromosome evolution by the draft genome of Drosophila albomicans VL - 13 ER - TY - JOUR AB - Many species have morphologically and genetically differentiated sex chromosomes, such as the XY pair of mammals. Y chromosomes are often highly degenerated and carry few functional genes, so that XY males have only one copy of most Xlinked genes (whereas females have two). As a result, chromosome-wide mechanisms of dosage compensation, such as the mammalian X-inactivation, often evolve to reestablish expression balance. A similar phenomenon is expected in femaleheterogametic species, where ZW females should suffer from imbalances due to W-chromosome degeneration. However, no global dosage compensation mechanisms have been detected in the two independent ZW systems that have been studied systematically (birds and silkworm), leading to the suggestion that lack of global dosage compensation may be a general feature of female-heterogametic species. However, analyses of other independently evolved ZW systems are required to test if this is the case. In this study, we use published genomic and expression data to test for the presence of global dosage compensation in Schistosoma mansoni, a trematode parasite that causes schistosomiasis in humans. We find that Z-linked expression is reduced relative to autosomal expression in females but not males, consistent with incomplete or localized dosage compensation. This gives further support to the theory that female-heterogametic species may not require global mechanisms of dosage compensation. AU - Vicoso, Beatriz AU - Bachtrog, Doris ID - 2072 IS - 1 JF - Genome Biology and Evolution TI - Lack of global dosage compensation in Schistosoma mansoni, a female-heterogametic parasite VL - 3 ER - TY - JOUR AB - The X or Z chromosome has several characteristics that distinguish it from the autosomes, namely hemizygosity in the heterogametic sex, and a potentially different effective population size, both of which may influence the rate and nature of evolution. In particular, there may be an accelerated rate of adaptive change for X-linked compared to autosomal coding sequences, often referred to as the Faster-X effect. Empirical studies have indicated that the strength of Faster-X evolution varies among different species, and theoretical treatments have shown that demography and mating system can substantially affect the degree of Faster-X evolution. Here we integrate genomic data on Faster-X evolution from a variety of animals with the demographic factors, mating system, and sex chromosome regulatory characteristics that may influence it. Our results suggest that differences in effective population size and mechanisms of dosage compensation may influence the perceived extent of Faster-X evolution, and help to explain several clade-specific patterns that we observe. AU - Mank, Judith E AU - Beatriz Vicoso AU - Berlin, Sofia AU - Charlesworth, Brian ID - 2071 IS - 3 JF - Evolution TI - Effective population size and the Faster-X effect: Empirical results and their interpretation VL - 64 ER - TY - JOUR AU - Beatriz Vicoso AU - Charlesworth, Brian ID - 2067 IS - 4 JF - Genetics TI - Recombination rates may affect the ratio of X to autosomal noncoding polymorphism in African populations of Drosophila melanogaster VL - 181 ER - TY - JOUR AB - In Drosophila, there is a consistent deficit of male-biased genes on the X chromosome. It has been suggested that male-biased genes may evolve from initially unbiased genes as a result of increased expression levels in males. If transcription rates are limited, a large increase in expression in the testis may be harder to achieve for single-copy X-linked genes than for autosomal genes, because they are already hypertranscribed due to dosage compensation. This hypothesis predicts that the larger the increase in expression required to make a male-biased gene, the lower the chance of this being achievable if it is located on the X chromosome. Consequently, highly expressed male-biased genes should be located on the X chromosome less often than lowly expressed male-biased genes. This pattern is observed in our analysis of publicly available data, where microarray data or EST data are used to detect male-biased genes in D. melanogaster and to measure their expression levels. This is consistent with the idea that limitations in transcription rates may prevent male-biased genes from accumulating on the X chromosome. AU - Beatriz Vicoso AU - Charlesworth, Brian ID - 2068 IS - 5 JF - Journal of Molecular Evolution TI - The deficit of male-biased genes on the D. melanogaster X chromosome is expression-dependent: A consequence of dosage compensation? VL - 68 ER - TY - JOUR AB - Current models of X-linked and autosomal evolutionary rates often assume that the effective population size of the X chromosome (NeX) is equal to three-quarters of the autosomal population size (NeA). However, polymorphism studies of Drosophila melanogaster and D. simulans suggest that there are often significant deviations from this value. We have computed fixation rates of beneficial and deleterious mutations at X-linked and autosomal sites when this occurs. We find that NeX/NeA is a crucial parameter for the rates of evolution of X-linked sites compared to autosomal sites. Faster-X evolution due to the fixation of beneficial mutations can occur under a much wider range of levels of dominance when NeX/N eA > 3/4. We also examined various parameters that are known to influence the rates of evolution at X-linked and autosomal sites, such as different mutation rates in males and females and mutations that are sexually antagonistic, to determine which cases can lead to faster-X evolution. We show that, when the rate of nonsynonymous evolution is normalized by the rate of neutral evolution, a sex difference in mutation rate has no influence on the conditions for faster-X evolution. AU - Beatriz Vicoso AU - Charlesworth, Brian ID - 2069 IS - 9 JF - Evolution TI - Effective population size and the faster-X effect: An extended model VL - 63 ER - TY - JOUR AB - In many eukaryotic organisms, gender is determined by a pair of heteromorphic sex chromosomes. Degeneration of the non-recombining Y chromosome is a general facet of sex chromosome evolution. Selective pressure to restore expression levels of X-linked genes relative to autosomes accompanies Y-chromosome degeneration, thus driving the evolution of dosage compensation mechanisms. This review focuses on evolutionary aspects of dosage compensation, in light of recent advances in comparative and functional genomics that have substantially increased our understanding of the molecular mechanisms of dosage compensation and how it evolved. We review processes involved in sex chromosome evolution, and discuss the dynamic interaction between Y degeneration and the acquisition of dosage compensation. We compare mechanisms of dosage compensation and the origin of dosage compensation genes between different taxa and comment on sex chromosomes that apparently lack compensation mechanisms. Finally, we discuss how dosage compensation systems can also influence the evolution of well-established sex chromosomes. AU - Beatriz Vicoso AU - Bachtrog, Doris ID - 2070 IS - 5 JF - Chromosome Research TI - Progress and prospects toward our understanding of the evolution of dosage compensation VL - 17 ER - TY - JOUR AB - Population genetics models show that, under certain conditions, the X chromosome is expected to be under more efficient selection than the autosomes. This could lead to 'faster-X evolution', if a large proportion of mutations are fixed by positive selection, as suggested by recent studies in Drosophila. We used a multispecies approach to test this: Muller's element D, an autosomal arm, is fused to the ancestral X chromosome in Drosophila pseudoobscura and its sister species, Drosophila affinis. We tested whether the same set of genes had higher rates of non-synonymous evolution when they were X-linked (in the D. pseudoobscura/D. affinis comparison) than when they were autosomal (in Drosophila melanogaster/Drosophila yakuba). Although not significant, our results suggest this may be the case, but only for genes under particularly strong positive selection/weak purifying selection. They also suggest that genes that have become X-linked have higher levels of codon bias and slower synonymous site evolution, consistent with more effective selection on codon usage at X-linked sites. AU - Beatriz Vicoso AU - Haddrill, Penelope R AU - Charlesworth, Brian ID - 2065 IS - 5 JF - Genetical Research TI - A multispecies approach for comparing sequence evolution of X-linked and autosomal sites in Drosophila VL - 90 ER - TY - JOUR AB - Although the X chromosome is usually similar to the autosomes in size and cytogenetic appearance, theoretical models predict that its hemizygosity in males may cause unusual patterns of evolution. The sequencing of several genomes has indeed revealed differences between the X chromosome and the autosomes in the rates of gene divergence, patterns of gene expression and rates of gene movement between chromosomes. A better understanding of these patterns should provide valuable information on the evolution of genes located on the X chromosome. It could also suggest solutions to more general problems in molecular evolution, such as detecting selection and estimating mutational effects on fitness AU - Beatriz Vicoso AU - Charlesworth, Brian ID - 2066 IS - 8 JF - Nature Reviews Genetics TI - Evolution on the X chromosome: Unusual patterns and processes VL - 7 ER -