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345 results for “Sex chromosome”
Data from: Sex-determining chromosomes and sexual dimorphism: insights from genetic mapping of sex expression in a natural hybrid Fragaria × ananassa subsp. cuneifolia
We studied the natural hybrid (Fragaria × ananassa subsp. cuneifolia) between two sexually dimorphic octoploid strawberry species (Fragaria virginiana and Fragaria chiloensis) to gain insight into the dynamics of sex chromosomes and the genesis of sexual dimorphism. Male sterility is dominant in both the parental species and thus will be inherited maternally, but the chromosome that houses the sex-determining region differs. Thus, we asked whether (1) the cytotypic composition of hybrid populations represents one or both maternal species, (2) the sex-determining chromosome of the hybrid reflects the location of male sterility within the maternal donor species and (3) crosses from the hybrid species show less sexual dimorphism than the parental species. We found that F. × ananassa subsp. cuneifolia populations consisted of both parental cytotypes but one predominated within each population. Genetic linkage mapping of two crosses showed dominance of male sterility similar to the parental species, however, the map location of male sterility reflected the maternal donor in one cross, but not the other. Moreover, female function mapped to a single region in the first cross, but to two regions in the second cross. Aside from components of female function (fruit set and seed set), other traits that have been found to be significantly sexually dimorphic in the pure species were either not dimorphic or were dimorphic in the opposite direction to the parental species. These results suggest that hybrids experience some disruption of dimorphism in secondary sexual traits, as well as novel location and number of quantitative trait locus (QTL) affecting sex function.
Fitness consequences of a non-recombining sex-ratio drive chromosome can explain its prevalence in the wild
<p>Understanding the pleiotropic consequences of gene drive systems on host fitness is essential to predict their spread through a host population. Here we study Sex-ratio (SR) X-chromosome drive in the fly Drosophila recens, where SR causes the death of Y-bearing sperm in male carriers. SR males only sire daughters, which all carry SR, thus giving the chromosome a transmission advantage. The prevalence of the SR chromosome appears stable, suggesting pleiotropic costs. It was previously shown that females homozygous for SR are sterile, and here we test for additional fitness costs of SR. We find that females heterozygous for SR have reduced fecundity and that male SR carriers have reduced fertility in conditions of sperm competition. We then use our fitness estimates to parameterize theoretical models of SR drive and show that the decrease in fecundity and sperm competition performance can account for the observed prevalence of SR in natural populations. In addition, we find that the expected equilibrium frequency of the SR chromosome is particularly sensitive to the degree of multiple mating and performance in sperm competition. Together our data suggest that the mating system of the organism should be carefully considered during the development of gene drive systems.</p>
Data from: Cryptic recombination in the ever-young sex chromosomes of Hylid frogs
Sex chromosomes are expected to evolve suppressed recombination, which leads to degeneration of the Y and heteromorphism between the X and Y. Some sex chromosomes remain homomorphic, however, and the factors that prevent degeneration of the Y in these cases are not understood. The homomorphic sex chromosomes of the European tree frogs (Hyla spp.) present an interesting paradox. Recombination in males has never been observed in crossing experiments, but molecular data are suggestive of occasional recombination between the X and Y. The hypothesis that these sex chromosomes recombine has not been tested statistically, however, nor has the XY recombination rate been estimated. Here we use Approximate Bayesian Computation coupled with coalescent simulations of sex chromosomes to quantify X-Y recombination rate from existent data. We find that microsatellite data from H. arborea, H. intermedia, and H. molleri support a recombination rate between X and Y that is significantly different from zero. We estimate that rate to be approximately 105 times smaller than that between X chromosomes. Our findings support the notion that very low recombination rate may be sufficient to maintain homomorphism in sex chromosomes.
Data from: Opposing patterns of intraspecific and interspecific differentiation in sex chromosomes and autosomes
Linking intraspecific and interspecific divergence is an important challenge in speciation research. X chromosomes are expected to evolve faster than autosomes and disproportionately contribute to reproductive barriers, and comparing genetic variation on X and autosomal markers within and between species can elucidate evolutionary processes that shape genome variation. We performed RADseq on a 16-population transect of two closely-related Australian cricket species, Teleogryllus commodus and T. oceanicus, covering allopatry and sympatry. This classic study system for sexual selection provides a rare exception to Haldane's rule, as hybrid females are sterile. We found no evidence of recent introgression, despite the fact that the species co-exist in overlapping habitats in the wild and interbreed in the laboratory. Putative X-linked loci showed greater differentiation between species compared to autosomal loci. However, population differentiation within species was unexpectedly lower on X-linked markers than autosomal markers, and relative X-to-autosomal genetic diversity was inflated above neutral expectations. Populations of both species showed genomic signatures of recent population expansions, but these were not strong enough to account for the inflated X/A diversity. Instead, most of the excess polymorphism on the X could better be explained by sex-biased processes that increase the relative effective population size of the X, such as interspecific variation in the strength of sexual selection among males. Taken together, the opposing patterns of diversity and differentiation at X versus autosomal loci implicate a greater role for sex-linked genes in maintaining species boundaries in this system.
Data from: Differential divergence in autosomes and sex chromosomes is associated with intra-island diversification at a very small spatial scale in a songbird lineage
<p>Recently diverged taxa showing marked phenotypic and ecological diversity are optimal systems to understand the genetic processes underlying speciation. We used genome-wide markers to investigate the diversification of the Reunion grey white eye (<i>Zosterops borbonicus</i>) on the small volcanic island of Reunion (Mascarene archipelago), where this species complex exhibits four geographic forms that are parapatrically distributed across the island and differ strikingly in plumage colour. One form restricted to the highlands is separated by a steep ecological gradient from three distinct lowland forms which meet at narrow hybrid zones that are not associated with environmental variables. Analyses of genomic variation based on SNP data from genotyping-by-sequencing and pooled RADseq approaches, reveal that signatures of selection associated with elevation can be found at multiple regions across the genome, whereas most loci associated with the lowland forms are located on the Z sex chromosome. We identified <i>TYRP1</i>, a Z-linked colour gene, as a likely candidate locus underlying colour variation among lowland forms. Tests of demographic models revealed that highland and lowland forms diverged in the presence of gene flow, and divergence has progressed as gene flow was restricted by selection at loci across the genome. This system is promising to investigate how natural selection and reproductive isolation shape the genomic landscape of divergence at multiple stages of the speciation process.</p>
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.
FIGURES 16–21. Endecous ubajarensis n in A new species of Endecous Saussure, 1878 (Orthoptera, Gryllidae) from northeast Brazil with the first X X 0 chromosomal sex system in Gryllidae
FIGURES 16–21. Endecous ubajarensis n. sp. female UBA02. 16—subgenital plate; 17—supranal plate; 18—ovipositor, ventral view; 19—ovipositor, lateral view; 20—ovipositor apex, dorsal view; 21—ovipositor apex, lateral view.
FIGURES 12–15. Endecous ubajarensis n in A new species of Endecous Saussure, 1878 (Orthoptera, Gryllidae) from northeast Brazil with the first X X 0 chromosomal sex system in Gryllidae
FIGURES 12–15. Endecous ubajarensis n. sp. phallic sclerites of the paratype UBA03. 12—dorsal view; 13—ventral view; 14—diagonal view; 15—posterior view. Conventions: Ps.Arm—pseudepiphallic arm; Ps.db—pseudepiphallic dorsal branch; Ps.vb—pseudepiphallic ventral branch; Ps.P—pseudepiphallic paramere; Ps.ib—Pseudepiphallic sclerite inner bars; Ps.mspseudepiphallic membranous shield; Ect.Arc—ectophallic arc; Ect.lb—ectophallic lateral bar; Ect.mp—ectophallic median projection; Ect.Ap—ectophallic apodeme; End.Sc.a—endophallic sclerite anterior portion; End.Sc.p—endophallic sclerite posterior portion.
FIGURES 3–11. Endecous ubajarensis n in A new species of Endecous Saussure, 1878 (Orthoptera, Gryllidae) from northeast Brazil with the first X X 0 chromosomal sex system in Gryllidae
FIGURES 3–11. Endecous ubajarensis n. sp. holotype morphology. 3–5—habitus in lateral, dorsal, and ventral views, respectively; 6—head, frontal view; 7—supranal-plate; 8—subgenital plate; 9a, b, c—tibia III outer apical spurs; arrow, distal subapical spur; 10d, e, f, g—inner apical spurs; 11—tibia and tarsus, lateral view; arrow, distal subapical spur.
FIGURE 5 in A new species of Synotaxus and the first chromosomal study on Synotaxidae, presenting a rare XY sex chromosome system in spiders (Araneae, Araneoidea)
FIGURE 5. Mitotic telocentric chromosomes of Synotaxus jaraguari n. sp. A, Spermatogonial metaphase 2n♂ = 22 + XY. B– C, Oogonial metaphases. B, 2n♀= 22 + XX. C. 2n♀ = 26. Scale bar, 5 µm.
FIGURE 4. Synotaxus jaraguari n in A new species of Synotaxus and the first chromosomal study on Synotaxidae, presenting a rare XY sex chromosome system in spiders (Araneae, Araneoidea)
FIGURE 4. Synotaxus jaraguari n. sp. A. Male palp, ventral view. B, Ditto, retrolateral view. C, Epigynum, ventral view. D, Female internal genitalia, dorsal view. Abbreviations: AB, Anterior border of epigynum; AS, Accessory sac; MA, Median apophysis; PA, Patellar apophysis; PC, Paracymbium; PP, Patellar projection, TTA, Theridioid tegular apophysis; FD, Fertilization ducts; SP, Spermathecae. Scale bar, 0.5 mm.
FIGURE 7 in A new species of Synotaxus and the first chromosomal study on Synotaxidae, presenting a rare XY sex chromosome system in spiders (Araneae, Araneoidea)
FIGURE 7. Scheme showing hypothetical origin of the karyotype 2n♂ = 22 + XY, found in Synotaxus jaraguari n. sp.
FIGURE 6 in A new species of Synotaxus and the first chromosomal study on Synotaxidae, presenting a rare XY sex chromosome system in spiders (Araneae, Araneoidea)
FIGURE 6. Chromosomes of Synotaxus jaraguari n. sp., male. A–C, Giemsa stained. D, Silver nitrate impregnation. A–B, Diplotenes, with 11 autosomal bivalents + XY, showing the achiasmatic association between X and Y (A, photo and inset) and its early segregation (B). C, Metaphase II with n = 12. D, Spermatogonial metaphase, with 2n♂ = 24, highlighting the Nucleolar Organizer Regions (arrows). Scale bar, 5 µm.
FIGURE 3. Synotaxus jaraguari n in A new species of Synotaxus and the first chromosomal study on Synotaxidae, presenting a rare XY sex chromosome system in spiders (Araneae, Araneoidea)
FIGURE 3. Synotaxus jaraguari n. sp., male palp. A, Theridioid tegular apophysis, lateral view. B–D, Paracymbium and patelar apophysis. B, Lateral view. C, Ventro-lateral view. D, Detail, ventral view. Abbreviations: C, Cymbium; PA, Patellar apophysis; PC, Paracymbium; PP, Patellar projection, TTA, Theridioid tegular apophysis.
FIGURE 2. Synotaxus jaraguari n in A new species of Synotaxus and the first chromosomal study on Synotaxidae, presenting a rare XY sex chromosome system in spiders (Araneae, Araneoidea)
FIGURE 2. Synotaxus jaraguari n. sp. A–D, Male. A, Carapace, frontal view. B, Lateral view. C, Horn, detail, frontal view. D, Lateral view. E–F, Palp. E, Ventral view. F, Theridioid tegular apophysis, detail. Abbreviations: E, embolus; TTA, Theridioid tegular apophysis.
FIGURES 13–22 in A novel multiple sex chromosome system in Orthoptera, found in the tree cricket Oecanthus rubromaculatus Zefa, 2022 (Grylloidea, Oecanthidae)
FIGURES 13–22. Schematic model showing the phases of karyotypic derivation since the ancestral karyotype of 2n = 21, X0♂/ XX♀ based com Oecanthus pictus, from to 2n = 12, X1X2X3Y1Y2Y3♂/X1X1X2X2X3X3♀ of the Oecanthus rubromaculatus. 13, Ancestral karyotype with 2n = 21, X0♂/XX♀; 14, Heterozygous karyotype with 2n = 18, X0♂ after Robertsonian translocation between pair 4/5, 6/7 and 8/9; 15–16, Homozygous karyotype with 2n = 15, X0♂ after reciprocal translocation between pair 4/5, 6/7 and 8/9 (chromosomes in the box are involved in tandem fusion to form the neo-XY sex-system); 17–18, Karyotype with 2n = 14, neo-XY♂ (chromosomes in the box are involved in Robertsonian translocation to form the neo-X1X2Y♂ sex-system); 19–20, Karyotype with 2n = 13, X1X2Y♂ (chromosomes in the box are involved in Robertsonian translocation to form the neo-X1X2Y1Y2♂ sex-system found in individuals from São Francisco de Paula); 21–22, Karyotype with 2n = 12, X1X2Y1Y2♂ (chromosomes in the box are involved in translocation to form the neo-X1X2X3Y1Y2Y3♂ sex-system found in individuals from Pelotas). Chromosome breakpoints for rearrangements were indicated with yellow lines; L = small centromeric chromosome lost in the process.
FIGURES 9–12 in A novel multiple sex chromosome system in Orthoptera, found in the tree cricket Oecanthus rubromaculatus Zefa, 2022 (Grylloidea, Oecanthidae)
FIGURES 9–12. Chromosomes of Oecanthus rubromaculatus from Pelotas. 9, Male karyotype with 2n = 12, X 1 X 2 X 3 Y 1 Y 2 Y 3. 10, Initial Diplotene stage highlighting the heteropycnotic X chromosome, distanced from the other sex chromosomes by a chromatin thread (arrow); 11, Diplotene stage with emphasis on the sex chromosome chain; 12, Sister Metaphases II.
FIGURES 1–8 in A novel multiple sex chromosome system in Orthoptera, found in the tree cricket Oecanthus rubromaculatus Zefa, 2022 (Grylloidea, Oecanthidae)
FIGURES 1–8. Chromosomes of Oecanthus rubromaculatus from São Francisco de Paula. 1, karyotype of the female with 2n = 12, X1X1X2X2 (Best mitotic Metaphase found, but missing one of the bivalents from pair 4); 2, complete female mitotic Metaphase; 3–5, Male's Diplotene stages highlighting the heteropycnotic X chromosome, distanced from the other sexchromosomes by a chromatin thread (arrow); 6, Metaphase I; 7, Anaphase I; 8, Sister Metaphases II.
Karyotype diversification and evolution in Silene (Caryophyllaceae) representatives with sex chromosomes: taxonomic and biogeographical implications
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Diversity of sex chromosomes in Sulawesian medaka fishes
<p><span>Recent genetic and genomic studies have revealed tremendous diversity in sex chromosomes across diverse taxa. Closely related species with different sex chromosomes provide us with excellent opportunities to investigate the driving forces and the consequences of sex chromosome turnover. In the present study, we investigated the diversity of sex chromosomes of 13 <em>Oryzias</em> species from Sulawesi, Indonesia, which diversified during the last 4.86 million years. Using pooled sequencing we found sex chromosomes in 9 species that all had XY systems, with a species being possibly modified by multiple loci. Seven species (<em>O. woworae</em>, <em>O</em>. <em>asinua</em>, <em>O</em>. <em>wolasi</em>, <em>O</em>. <em>matanensis</em>, <em>O</em>. <em>celebensis</em>, <em>O</em>. <em>hadiatyae</em>, and <em>O</em>. <em>dopingdopingensis</em>) share linkage group (LG) 24 as sex chromosomes; however, they differed in the length and magnitude of sequence divergence between the X and Y chromosomes. The sex chromosome of <em>O</em>. <em>eversi</em> was LG4, which has not been reported as a sex chromosome in any other medaka species. In <em>O</em>. <em>sarasinorum</em>, LG16 and LG22 are associated with sex. Although LG16 was found to be sex-linked in another medaka species previously examined, the sex-determining regions did not overlap. No significant signatures for sex chromosomes were identified in the other 4 species (<em>O</em>. <em>marmoratus</em>, <em>O</em>. <em>nigrimas</em>, <em>O</em>. <em>nebulosus</em>, and <em>O</em>. <em>orthognathus</em>). Frequent turnovers and the great diversity of the sex chromosomes will make Sulawesian medaka species a model system for investigating the driving forces and consequences of sex chromosome turnover.</span></p>
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