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19 results for “sex-chromosome”
Data from: Rewinding the ratchet: Rare recombination locally rescues neo-W degeneration and generates plateaus of sex-chromosome divergence
<p>Natural selection is less efficient in the absence of recombination. As a result, non-recombining sequences, such as sex chromosomes, tend to degenerate over time. Although the outcomes of recombination arrest are typically observed after many millions of generations, recent neo-sex chromosomes can give insight into the early stages of this process. Here we investigate the evolution of neo-sex chromosomes in the Spanish marbled white butterfly, <em>Melanargia ines</em>, where a Z-autosome fusion has turned the homologous autosome into a non-recombining neo-W chromosome. We show that these neo-sex chromosomes are likely limited to the Iberian population of <em>M. ines</em>, and that they arose around the time when this population split from North-African populations, around 1.5 million years ago. Recombination arrest of the neo-W chromosome has led to an excess of premature stop codons and frameshift mutations, and reduced gene expression compared to the neo-Z chromosome. Surprisingly, we identified two regions of 1 Mb at one end of the neo-W that are both less diverged from the neo-Z and less degraded than the rest of the chromosome, suggesting a history of rare but repeated genetic exchange between the two neo-sex chromosomes. These plateaus of neo-sex chromosome divergence suggest that neo-W degradation can be locally reversed by rare recombination between neo-W and neo-Z chromosomes.</p>
Data from: Rewinding the ratchet: Rare recombination locally rescues neo-W degeneration and generates plateaus of sex-chromosome divergence
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Data from: Evolution of multiple sex-chromosomes associated with dynamic genome reshuffling in Leptidea wood-white butterflies
<p>Sex chromosome systems tend to be highly conserved and knowledge about their evolution typically comes from macroevolutionary inferences. Rapidly evolving complex sex chromosome systems represent a rare opportunity to study the mechanisms of sex chromosome evolution at unprecedented resolution. Three cryptic species of wood white butterflies – <i><span>Leptidea juvernica</span></i>, <i><span>L. sinapis</span></i>, and <i><span>L. reali</span></i> – have each a unique set of multiple sex chromosomes with 3–4 W and 3–4 Z chromosomes. Using a transcriptome-based microarray for comparative genomic hybridization (array-CGH) and a library of bacterial artificial chromosome (BAC) clones, both developed in <i><span>L. juvernica</span></i>, we identified Z-linked <i><span>Leptidea</span></i> orthologs of <i><span>Bombyx mori</span></i> genes and mapped them by fluorescence <i><span>in situ</span></i> hybridization (FISH) with BAC probes on multiple Z chromosomes. In all three species, we determined synteny blocks of autosomal origin and reconstructed the evolution of multiple sex chromosomes. In addition, we identified W-homologs of Z-linked orthologs and characterized their molecular differentiation. Our results suggest that the multiple sex chromosome system evolved in a common ancestor of these three <i><span>Leptidea</span></i> species as a result of dynamic genome reshuffling through repeated rearrangements between the sex chromosomes and autosomes, including translocations and fissions. Thus, the sex chromosome turnover could not play a role in reproductive isolation between the <i><span>Leptidea </span></i>species studied. However, we suggest that subsequent species-specific rearrangements of multiple sex chromosomes, along with different rates of neo-W chromosome degeneration and significantly increased number of Z-linked genes could accelerate the accumulation of genetic incompatibilities between populations and promote their divergence resulting in speciation.</p>
Data from: Sex-chromosome recombination in common frogs brings water to the fountain-of-youth
According to the canonical model of sex-chromosome evolution, the degeneration of Y or W chromosomes (as observed in mammals and birds respectively) results from an arrest of recombination in the heterogametic sex, driven by the fixation of sexually antagonistic mutations. However, sex chromosomes have remained homomorphic in many lineages of fishes, amphibians, and non-avian reptiles. According to the 'fountain-of-youth' model, this homomorphy results from occasional events of sex reversal. If recombination arrest in males is controlled by maleness per se (and not by genotype), then Y chromosomes are expected to recombine in XY females, preventing their long-term degeneration. Here we provide field support for the fountain-of-youth, by showing that sex-chromosome recombination in Rana temporaria only depends on phenotypic sex: naturally-occurring XX males show the same restriction of recombination as XY males (average map length ~2 cM), while XY females recombine as much as XX females (average map length ~150 cM). Our results challenge several common assumptions regarding the evolution of sex chromosomes, including the role of sexually antagonistic genes as drivers of recombination arrest, and that of chromosomal inversions as underlying mechanisms.
Data from: Dmrt1 polymorphism and sex-chromosome differentiation in Rana temporaria
Sex-determination mechanisms vary both within and among populations of common frogs, opening opportunities to investigate the molecular pathways and ultimate causes shaping their evolution. We investigated the association between sex-chromosome differentiation (as assayed from microsatellites) and polymorphism at the candidate sex-determining gene Dmrt1 in two Alpine populations. Both populations harboured a diversity of X-linked and Y-linked Dmrt1 haplotypes. Some males had fixed male-specific alleles at all markers ("differentiated" Y chromosomes), others only at Dmrt1 ("proto-" Y chromosomes), while still others were genetically indistinguishable from females (undifferentiated X chromosomes). Besides these XX males, we also found rare XY females. The several Dmrt1 Y haplotypes differed in the probability of association with a differentiated Y chromosome, which we interpret as a result of differences in the masculinizing effects of alleles at the sex-determining locus. From our results, the polymorphism in sex-chromosome differentiation and its association with Dmrt1, previously inferred from Swedish populations, are not just idiosyncratic features of peripheral populations, but also characterize highly diverged populations in the central range. This implies that an apparently unstable pattern has been maintained over long evolutionary times.
Data from: Sex-chromosome differentiation and 'sex races' in the common frog (Rana temporaria)
Sex-chromosome differentiation was recently shown to vary among common frog populations in Fennoscandia, suggesting a trend of increased differentiation with latitude. By rearing families from two contrasted populations (respectively, from northern and southern Sweden), we show this disparity to stem from differences in sex-determination mechanisms rather than in XY-recombination patterns. Offspring from the northern population display equal sex ratios at metamorphosis, with phenotypic sexes that correlate strongly with paternal LG2 haplotypes (the sex chromosome); accordingly, Y haplotypes are markedly differentiated, with male-specific alleles and depressed diversity testifying to their smaller effective population size. In the southern population, by contrast, a majority of juveniles present ovaries at metamorphosis; only later in development do sex ratios return to equilibrium. Even at these later stages, phenotypic sexes correlate only mildly with paternal LG2 haplotypes; accordingly, there are no recognizable Y haplotypes. These distinct patterns of gonadal development fit the concept of 'sex races' proposed in the 1930s, with our two populations assigned to the 'differentiated' and 'semi-differentiated' races, respectively. Our results support the suggestion that 'sex races' differ in the genetic versus epigenetic components of sex determination. Analysing populations from the 'undifferentiated race' with high-density genetic maps should help to further test this hypothesis.
Data from: Sex-chromosome differentiation parallels post-glacial range expansion in European tree frogs (Hyla arborea).
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Data from: Sex-chromosome differentiation and ‘sex races’ in the common frog (Rana temporaria)
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Data from: Sex-chromosome recombination in common frogs brings water to the fountain-of-youth
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Phylogeography, more than elevation, accounts for sex-chromosome differentiation in Swiss populations of the common frog (Rana temporaria)
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Data from: Evolution of multiple sex-chromosomes associated with dynamic genome reshuffling in Leptidea wood-white butterflies
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Data from: Geographic variation in sex-chromosome differentiation in the common frog (Rana temporaria)
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Data from: Dmrt1 polymorphism and sex-chromosome differentiation in Rana temporaria
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Data from: Sex-chromosome turnovers induced by deleterious mutation load
In sharp contrast with mammals and birds, many cold-blooded vertebrates present homomorphic sex chromosomes. Empirical evidence supports a role for frequent turnovers, which replace non-recombining sex chromosomes before they have time to decay. Three main mechanisms have been proposed for such turnovers, relying either on neutral processes, sex-ratio selection, or intrinsic benefits of the new sex-determining genes (due e.g. to linkage with sexually antagonistic mutations). Here we suggest an additional mechanism, arising from the load of deleterious mutations that accumulate on non-recombining sex chromosomes. In the absence of dosage compensation, this load should progressively lower survival rate in the heterogametic sex. Turnovers should occur when this cost outweighs the benefits gained from any sexually antagonistic genes carried by the non-recombining sex chromosome. We use individual-based simulations of a Muller's ratchet process to test this prediction, and investigate how the relevant parameters (effective population size, strength and dominance of deleterious mutations, size of non-recombining segment, and strength of sexually antagonistic selection) are expected to affect the rate of turnovers.
Data from: Sex-chromosome turnovers induced by deleterious mutation load
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Data from: Dobzhansky-Muller incompatibilities, dominance drive, and sex-chromosome introgression at secondary contact zones: a simulation study
Dobzhansky-Muller (DM) incompatibilities involving sex chromosomes have been proposed to account for Haldane's rule (lowered fitness among hybrid offspring of the heterogametic sex) as well as Darwin's corollary (asymmetric fitness costs with respect to the direction of the cross). We performed simulation studies of a hybrid zone to investigate the effects of different types of DM incompatibilities on cline widths and positions of sex-linked markers. From our simulations, X-Y incompatibilities generate steep clines for both X-linked and Y-linked markers; random effects may produce strong noise in cline center positions when migration is high relative to fitness costs, but X- and Y-centers always coincide strictly. X-autosome and Y-autosome incompatibilities also generate steep clines, but systematic shifts in cline centers occur when migration is high relative to selection, as a result of a dominance drive linked to Darwin's corollary. Interestingly, sex-linked genes always show farther introgression than the associated autosomal genes. We discuss ways of disentangling the potentially confounding effects of sex biases in migration, we compare our results to those of a few documented contact zones, and we stress the need to study independent replicates of the same contact zone.
Clinical and Genetic Aspects of Fetuses With Sex-chromosome Disorders
ClinicalTrials.gov study NCT07304193. IPD Sharing: Not stated. Countries: 1. Publications: 0.
Data from: Dobzhansky-Muller incompatibilities, dominance drive, and sex-chromosome introgression at secondary contact zones: a simulation study
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HSF1 regulates transcription of sex-chromosomal multicopy genes during post-meiotic repression
GEO Series GSE22492. Mus musculus. 3 samples. Type: Genome binding/occupancy profiling by genome tiling array.
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Allen Brain Atlas
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International Brain Laboratory public data
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OpenNeuro
OpenNeuro is a free, open platform for sharing neuroimaging datasets, with public search, dataset pages, and download paths for web, S3, DataLad, and the OpenNeuro CLI.