Journal articles: 'Homomorphic sex chromosomes'

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Ogata, Mitsuaki, Kazuo Suzuki, Yoshiaki Yuasa, and Ikuo Miura. "Sex chromosome evolution from a heteromorphic to a homomorphic system by inter-population hybridization in a frog." Philosophical Transactions of the Royal Society B: Biological Sciences 376, no. 1833 (July 26, 2021): 20200105. http://dx.doi.org/10.1098/rstb.2020.0105.

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Sex chromosomes generally evolve from a homomorphic to heteromorphic state. Once a heteromorphic system is established, the sex chromosome system may remain stable for an extended period. Here, we show the opposite case of sex chromosome evolution from a heteromorphic to a homomorphic system in the Japanese frog Glandirana rugosa. One geographic group, Neo-ZW, has ZZ-ZW type heteromorphic sex chromosomes. We found that its western edge populations, which are geographically close to another West-Japan group with homomorphic sex chromosomes of XX-XY type, showed homozygous genotypes of sex-linked genes in both sexes. Karyologically, no heteromorphic sex chromosomes were identified. Sex-reversal experiments revealed that the males were heterogametic in sex determination. In addition, we identified another similar population around at the southwestern edge of the Neo-ZW group in the Kii Peninsula: the frogs had homomorphic sex chromosomes under male heterogamety, while shared mitochondrial haplotypes with the XY group, which is located in the east and bears heteromorphic sex chromosomes. In conclusion, our study revealed that the heteromorphic sex chromosome systems independently reversed back to or turned over to a homomorphic system around each of the western and southwestern edges of the Neo-ZW group through hybridization with the West-Japan group bearing homomorphic sex chromosomes. This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)’.

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Ma, Wen-Juan, and Paris Veltsos. "The Diversity and Evolution of Sex Chromosomes in Frogs." Genes 12, no. 4 (March 26, 2021): 483. http://dx.doi.org/10.3390/genes12040483.

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Frogs are ideal organisms for studying sex chromosome evolution because of their diversity in sex chromosome differentiation and sex-determination systems. We review 222 anuran frogs, spanning ~220 Myr of divergence, with characterized sex chromosomes, and discuss their evolution, phylogenetic distribution and transitions between homomorphic and heteromorphic states, as well as between sex-determination systems. Most (~75%) anurans have homomorphic sex chromosomes, with XY systems being three times more common than ZW systems. Most remaining anurans (~25%) have heteromorphic sex chromosomes, with XY and ZW systems almost equally represented. There are Y-autosome fusions in 11 species, and no W-/Z-/X-autosome fusions are known. The phylogeny represents at least 19 transitions between sex-determination systems and at least 16 cases of independent evolution of heteromorphic sex chromosomes from homomorphy, the likely ancestral state. Five lineages mostly have heteromorphic sex chromosomes, which might have evolved due to demographic and sexual selection attributes of those lineages. Males do not recombine over most of their genome, regardless of which is the heterogametic sex. Nevertheless, telomere-restricted recombination between ZW chromosomes has evolved at least once. More comparative genomic studies are needed to understand the evolutionary trajectories of sex chromosomes among frog lineages, especially in the ZW systems.

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Odierna, G., T. Caprigilone, L. A. Kupriyanova, and E. Olmo. "Further data on sex chromosomes of Lacertidae and a hypothesis on their evolutionary trend." Amphibia-Reptilia 14, no. 1 (1993): 1–11. http://dx.doi.org/10.1163/156853893x00147.

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AbstractSex chromosomes were studied in eight species of lacertid lizards using C-banding, G-banding and restriction enzyme treatment. All of the species showed female heterogamety. The W chromosome was a microchromosome in Lacerta graeca and Ophisops elegans. Two types of W were found in Lacerta vivipara; in specimens from The Netherlands it was metacentric, whereas in specimens from Russia it was acrocentric or subtelocentric. The W chromosome was homomorphic or nearly homomorphic but completely C-banded and heterochromatic in Lacerta agilis, Podarcis hispanica, Algyroides moreoticus and A. nigropunctatus. In was only possible to find sex chromosomes using the G-banding method in Podarcis sicula. The results obtained, together with data in the literature, suggest that sex chromosomes are likely to be present in all Lacertidae and that their differentiation took place repeatedly and independently in different taxa within the family. A model for sex chromosome evolution in the family, in which the starting point was the heterochromatization of the W chromosome, is proposed.

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Kuwana, Chiao, Hiroyuki Fujita, Masataka Tagami, Takanori Matsuo, and Ikuo Miura. "Evolution of Sex Chromosome Heteromorphy in Geographic Populations of the Japanese Tago’s Brown Frog Complex." Cytogenetic and Genome Research 161, no. 1-2 (2021): 23–31. http://dx.doi.org/10.1159/000512964.

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The sex chromosomes of most anuran amphibians are characterized by homomorphy in both sexes, and evolution to heteromorphy rarely occurs at the species or geographic population level. Here, we report sex chromosome heteromorphy in geographic populations of the Japanese Tago’s brown frog complex (2n = 26), comprising Rana sakuraii and R. tagoi. The sex chromosomes of R. sakuraii from the populations in western Japan were homomorphic in both sexes, whereas chromosome 7 from the populations in eastern Japan were heteromorphic in males. Chromosome 7 of R. tagoi, which is distributed close to R. sakuraii in eastern Japan, was highly similar in morphology to the Y chromosome of R. sakuraii. Based on this and on mitochondrial gene sequence analysis, we hypothesize that in the R. sakuraii populations from eastern Japan the XY heteromorphic sex chromosome system was established by the introduction of chromosome 7 from R. tagoi via interspecies hybridization. In contrast, chromosome 13 of R. tagoi from the 2 large islands in western Japan, Shikoku and Kyushu, showed a heteromorphic pattern of constitutive heterochromatin distribution in males, while this pattern was homomorphic in females. Our study reveals that sex chromosome heteromorphy evolved independently at the geographic lineage level in this species complex.

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Hime, Paul M., Jeffrey T. Briggler, Joshua S. Reece, and David W. Weisrock. "Genomic Data Reveal Conserved Female Heterogamety in Giant Salamanders with Gigantic Nuclear Genomes." G3: Genes|Genomes|Genetics 9, no. 10 (August 22, 2019): 3467–76. http://dx.doi.org/10.1534/g3.119.400556.

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Systems of genetic sex determination and the homology of sex chromosomes in different taxa vary greatly across vertebrates. Much progress remains to be made in understanding systems of genetic sex determination in non-model organisms, especially those with homomorphic sex chromosomes and/or large genomes. We used reduced representation genome sequencing to investigate genetic sex determination systems in the salamander family Cryptobranchidae (genera Cryptobranchus and Andrias), which typifies both of these inherent difficulties. We tested hypotheses of male- or female-heterogamety by sequencing hundreds of thousands of anonymous genomic regions in a panel of known-sex cryptobranchids and characterized patterns of presence/absence, inferred zygosity, and depth of coverage to identify sex-linked regions of these 56 gigabase genomes. Our results strongly support the hypothesis that all cryptobranchid species possess homologous systems of female heterogamety, despite maintenance of homomorphic sex chromosomes over nearly 60 million years. Additionally, we report a robust, non-invasive genetic assay for sex diagnosis in Cryptobranchus and Andrias which may have great utility for conservation efforts with these endangered salamanders. Co-amplification of these W-linked markers in both cryptobranchid genera provides evidence for long-term sex chromosome stasis in one of the most divergent salamander lineages. These findings inform hypotheses about the ancestral mode of sex determination in salamanders, but suggest that comparative data from other salamander families are needed. Our results further demonstrate that massive genomes are not necessarily a barrier to effective genome-wide sequencing and that the resulting data can be highly informative about sex determination systems in taxa with homomorphic sex chromosomes.

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Lisachov, Artem P., Vladimir A. Trifonov, Massimo Giovannotti, Malcolm A. Ferguson-Smith, and Pavel M. Borodin. "Heteromorphism of “Homomorphic” Sex Chromosomes in Two Anole Species (Squamata, Dactyloidae) Revealed by Synaptonemal Complex Analysis." Cytogenetic and Genome Research 151, no. 2 (2017): 89–95. http://dx.doi.org/10.1159/000460829.

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Iguanians (Pleurodonta) are one of the reptile lineages that, like birds and mammals, have sex chromosomes of ancient origin. In most iguanians these are microchromosomes, making a distinction between the X and Y as well as between homeologous sex chromosomes in other species difficult. Meiotic chromosome analysis may be used to elucidate their differentiation, because meiotic prophase chromosomes are longer and less condensed than metaphase chromosomes, and the homologues are paired with each other, revealing minor heteromorphisms. Using electron and fluorescent microscopy of surface spread synaptonemal complexes (SCs) and immunolocalization of the proteins of the SC (SYCP3), the centromere, and recombination nodules (MLH1), we examined sex chromosome synapsis and recombination in 2 species of anoles (Dactyloidae), Anolis carolinensis and Deiroptyx coelestinus, in which the sex chromosomes represent the ancestral condition of iguanians. We detected clear differences in size between the anole X and Y microchromosomes and found an interspecies difference in the localization of the pseudoautosomal region. Our results show that the apparent homomorphy of certain reptile sex chromosome systems can hide a cryptic differentiation, which potentially may influence the evolution of sexual dimorphism and speciation.

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Traut, W. "Sex determination in the fly Megaselia scalaris, a model system for primary steps of sex chromosome evolution." Genetics 136, no. 3 (March 1, 1994): 1097–104. http://dx.doi.org/10.1093/genetics/136.3.1097.

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Abstract The fly Megaselia scalaris Loew possesses three homomorphic chromosome pairs; 2 is the sex chromosome pair in two wild-type laboratory stocks of different geographic origin (designated "original" sex chromosome pair in this paper). The primary male-determining function moves at a very low rate to other chromosomes, thereby creating new Y chromosomes. Random amplified polymorphic DNA markers obtained by polymerase chain reaction with single decamer primers and a few available phenotypic markers were used in testcrosses to localize the sex-determining loci and to define the new sex chromosomes. Four cases are presented in which the primary male-determining function had been transferred from the original Y chromosome to a new locus either on one of the autosomes or on the original X chromosome, presumably by transposition. In these cases, the sex-determining function had moved to a different locus without an obvious cotransfer of other Y chromosome markers. Thus, with Megaselia we are afforded an experimental system to study the otherwise hypothetical primary stages of sex chromosome evolution. An initial molecular differentiation is apparent even in the new sex chromosomes. Molecular differences between the original X and Y chromosomes illustrate a slightly more advanced stage of sex chromosome evolution.

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Truţǎ, Elena, G. Cǎpraru, Ş. Surdu, M. M. Zamfirache, Z. Olteanu, C. M. Roşu, and L. Opricǎ. "Karyotypic Studies in Ecotypes of Hippophaë rhamnoides L. from Romania." Silvae Genetica 59, no. 1-6 (December 1, 2010): 175–82. http://dx.doi.org/10.1515/sg-2010-0021.

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Abstract Sea buckthorn is a dioecious Eurasian shrub or small tree with large morphological, biochemical and physiological variability, evidenced by the great number of studies. Cytogenetically, uncertainties exist on species basic number, ploidy level, and sex chromosomes. In this study, detailed cytogenetic measurements were carried out on six Romanian ecotypes belonging to Hippophaë rhamnoides L. ssp. carpatica Rousi, in order to establish the features and the symmetry degree of karyotypes, to evidence the sex chromosomes, and to construct the idiogram. The ecotypes have 2n = 24 metacentric and submetacentric chromosomes. An intraspecific variation exists concerning the proportion of these two morphotypes. The karyotypes have similar symmetry patterns (R = 2.57-2.89; TF%= 38.54-42.70; AsI%= 57.99-61.41; A1=0.27-0.35; A2 = 0.26-0.36) and belong to 1B and 2B classes, being relatively high symmetric. Based on obtained results, we presume that the male sex chromosomes are heteromorphic, while in female plants are homomorphic. The Y chromosome is larger than X chromosome.

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Sessions, Stanley K., Lilijana Bizjak Mali, David M. Green, Vladimir Trifonov, and Malcolm Ferguson-Smith. "Evidence for Sex Chromosome Turnover in Proteid Salamanders." Cytogenetic and Genome Research 148, no. 4 (2016): 305–13. http://dx.doi.org/10.1159/000446882.

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A major goal of genomic and reproductive biology is to understand the evolution of sex determination and sex chromosomes. Species of the 2 genera of the Salamander family Proteidae - Necturus of eastern North America, and Proteus of Southern Europe - have similar-looking karyotypes with the same chromosome number (2n = 38), which differentiates them from all other salamanders. However, Necturus possesses strongly heteromorphic X and Y sex chromosomes that Proteus lacks. Since the heteromorphic sex chromosomes of Necturus were detectable only with C-banding, we hypothesized that we could use C-banding to find sex chromosomes in Proteus. We examined mitotic material from colchicine-treated intestinal epithelium, and meiotic material from testes in specimens of Proteus, representing 3 genetically distinct populations in Slovenia. We compared these results with those from Necturus. We performed FISH to visualize telomeric sequences in meiotic bivalents. Our results provide evidence that Proteus represents an example of sex chromosome turnover in which a Necturus-like Y-chromosome has become permanently translocated to another chromosome converting heteromorphic sex chromosomes to homomorphic sex chromosomes. These results may be key to understanding some unusual aspects of demographics and reproductive biology of Proteus, and are discussed in the context of models of the evolution of sex chromosomes in amphibians.

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10

Filatov, Dmitry A. "Homomorphic plant sex chromosomes are coming of age." Molecular Ecology 24, no. 13 (June 26, 2015): 3217–19. http://dx.doi.org/10.1111/mec.13268.

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Chain, Frédéric J. J. "Sex-Biased Expression of Young Genes in Silurana (Xenopus) tropicalis." Cytogenetic and Genome Research 145, no. 3-4 (2015): 265–77. http://dx.doi.org/10.1159/000430942.

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Sex-biased gene expression can evolve from sex-specific selection and is often associated with sex-linked genes. Gene duplication is a particularly effective mechanism for the generation of sex-biased genes, in which a new copy can help resolve intralocus sexual conflicts. This study assesses sex-biased gene expression in an amphibian with homomorphic ZW sex chromosomes, the Western clawed frog Silurana (Xenopus)tropicalis. Previous work has shown that the sex chromosomes in this species are mainly undifferentiated and pseudoautosomal. Consistent with ongoing recombination between the sex chromosomes, this study detected little evidence for the general sexualization of sex-linked regions. A subset of genes closely linked to the sex determining locus displays a tendency for male-biased expression and elevated rates of evolution relative to genes in other genomic locations. This may be a symptom of an early stage of sex chromosome differentiation driven by, for example, chromosomal degeneration or natural selection on genes in this portion of the Z chromosome. Alternatively, it could reflect variation between the sexes in allelic copy number coupled with a lack of dosage compensation. Irrespective of the genomic location, lineage-specific genes and recently duplicated genes had significantly high levels of sex-biased expression, offering insights into the early transcriptional differentiation of young genes.

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Matveevsky, Sergey, Tsenka Chassovnikarova, Tatiana Grishaeva, Maret Atsaeva, Vasilii Malygin, Irina Bakloushinskaya, and Oxana Kolomiets. "Kinase CDK2 in Mammalian Meiotic Prophase I: Screening for Hetero- and Homomorphic Sex Chromosomes." International Journal of Molecular Sciences 22, no. 4 (February 17, 2021): 1969. http://dx.doi.org/10.3390/ijms22041969.

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Cyclin-dependent kinases (CDKs) are crucial regulators of the eukaryotic cell cycle. The critical role of CDK2 in the progression of meiosis was demonstrated in a single mammalian species, the mouse. We used immunocytochemistry to study the localization of CDK2 during meiosis in seven rodent species that possess hetero- and homomorphic male sex chromosomes. To compare the distribution of CDK2 in XY and XX male sex chromosomes, we performed multi-round immunostaining of a number of marker proteins in meiotic chromosomes of the rat and subterranean mole voles. Antibodies to the following proteins were used: RAD51, a member of the double-stranded DNA break repair machinery; MLH1, a component of the DNA mismatch repair system; and SUN1, which is involved in the connection between the meiotic telomeres and nuclear envelope, alongside the synaptic protein SYCP3 and kinetochore marker CREST. Using an enhanced protocol, we were able to assess the distribution of as many as four separate proteins in the same meiotic cell. We showed that during prophase I, CDK2 localizes to telomeric and interstitial regions of autosomes in all species investigated (rat, vole, hamster, subterranean mole voles, and mole rats). In sex bivalents following synaptic specificity, the CDK2 signals were distributed in three different modes. In the XY bivalent in the rat and mole rat, we detected numerous CDK2 signals in asynaptic regions and a single CDK2 focus on synaptic segments, similar to the mouse sex chromosomes. In the mole voles, which have unique XX sex chromosomes in males, CDK2 signals were nevertheless distributed similarly to the rat XY sex chromosomes. In the vole, sex chromosomes did not synapse, but demonstrated CDK2 signals of varying intensity, similar to the rat X and Y chromosomes. In female mole voles, the XX bivalent had CDK2 pattern similar to autosomes of all species. In the hamster, CDK2 signals were revealed in telomeric regions in the short synaptic segment of the sex bivalent. We found that CDK2 signals colocalize with SUN1 and MLH1 signals in meiotic chromosomes in rats and mole voles, similar to the mouse. The difference in CDK2 manifestation at the prophase I sex chromosomes can be considered an example of the rapid chromosome evolution in mammals.

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Hill, Peta, Foyez Shams, Christopher P. Burridge, Erik Wapstra, and Tariq Ezaz. "Differences in Homomorphic Sex Chromosomes Are Associated with Population Divergence in Sex Determination in Carinascincus ocellatus (Scincidae: Lygosominae)." Cells 10, no. 2 (February 1, 2021): 291. http://dx.doi.org/10.3390/cells10020291.

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Sex determination directs development as male or female in sexually reproducing organisms. Evolutionary transitions in sex determination have occurred frequently, suggesting simple mechanisms behind the transitions, yet their detail remains elusive. Here we explore the links between mechanisms of transitions in sex determination and sex chromosome evolution at both recent and deeper temporal scales (<1 Myr; ~79 Myr). We studied a rare example of a species with intraspecific variation in sex determination, Carinascincus ocellatus, and a relative, Liopholis whitii, using c-banding and mapping of repeat motifs and a custom Y chromosome probe set to identify the sex chromosomes. We identified both unique and conserved regions of the Y chromosome among C. ocellatus populations differing in sex determination. There was no evidence for homology of sex chromosomes between C. ocellatus and L. whitii, suggesting independent evolutionary origins. We discuss sex chromosome homology between members of the subfamily Lygosominae and propose links between sex chromosome evolution, sex determination transitions, and karyotype evolution.

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Roco, Álvaro S., Allen W. Olmstead, Sigmund J. Degitz, Tosikazu Amano, Lyle B. Zimmerman, and Mónica Bullejos. "Coexistence of Y, W, and Z sex chromosomes in Xenopus tropicalis." Proceedings of the National Academy of Sciences 112, no. 34 (July 27, 2015): E4752—E4761. http://dx.doi.org/10.1073/pnas.1505291112.

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Homomorphic sex chromosomes and rapid turnover of sex-determining genes can complicate establishing the sex chromosome system operating in a given species. This difficulty exists in Xenopus tropicalis, an anuran quickly becoming a relevant model for genetic, genomic, biochemical, and ecotoxicological research. Despite the recent interest attracted by this species, little is known about its sex chromosome system. Direct evidence that females are the heterogametic sex, as in the related species Xenopus laevis, has yet to be presented. Furthermore, X. laevis’ sex-determining gene, DM-W, does not exist in X. tropicalis, and the sex chromosomes in the two species are not homologous. Here we identify X. tropicalis’ sex chromosome system by integrating data from (i) breeding sex-reversed individuals, (ii) gynogenesis, (iii) triploids, and (iv) crosses among several strains. Our results indicate that at least three different types of sex chromosomes exist: Y, W, and Z, observed in YZ, YW, and ZZ males and in ZW and WW females. Because some combinations of parental sex chromosomes produce unisex offspring and other distorted sex ratios, understanding the sex-determination systems in X. tropicalis is critical for developing this flexible animal model for genetics and ecotoxicology.

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Waters, Paul D., and Jennifer A. Marshall Graves. "Monotreme sex chromosomes - implications for the evolution of amniote sex chromosomes." Reproduction, Fertility and Development 21, no. 8 (2009): 943. http://dx.doi.org/10.1071/rd09250.

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In vertebrates, a highly conserved pathway of genetic events controls male and female development, to the extent that many genes involved in human sex determination are also involved in fish sex determination. Surprisingly, the master switch to this pathway, which intuitively could be considered the most critical step, is inconsistent between vertebrate taxa. Interspersed in the vertebrate tree there are species that determine sex by environmental cues such as the temperature at which eggs are incubated, and then there are genetic sex-determination systems, with male heterogametic species (XY systems) and female heterogametic species (ZW systems), some of which have heteromorphic, and others homomorphic, sex chromosomes. This plasticity of sex-determining switches in vertebrates has made tracking the events of sex chromosome evolution in amniotes a daunting task, but comparative gene mapping is beginning to reveal some striking similarities across even distant taxa. In particular, the recent completion of the platypus genome sequence has completely changed our understanding of when the therian mammal X and Y chromosomes first arose (they are up to 150 million years younger than previously thought) and has also revealed the unexpected insight that sex determination of the amniote ancestor might have been controlled by a bird-like ZW system.

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Bista, Basanta, and Nicole Valenzuela. "Turtle Insights into the Evolution of the Reptilian Karyotype and the Genomic Architecture of Sex Determination." Genes 11, no. 4 (April 11, 2020): 416. http://dx.doi.org/10.3390/genes11040416.

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Sex chromosome evolution remains an evolutionary puzzle despite its importance in understanding sexual development and genome evolution. The seemingly random distribution of sex-determining systems in reptiles offers a unique opportunity to study sex chromosome evolution not afforded by mammals or birds. These reptilian systems derive from multiple transitions in sex determination, some independent, some convergent, that lead to the birth and death of sex chromosomes in various lineages. Here we focus on turtles, an emerging model group with growing genomic resources. We review karyotypic changes that accompanied the evolution of chromosomal systems of genotypic sex determination (GSD) in chelonians from systems under the control of environmental temperature (TSD). These transitions gave rise to 31 GSD species identified thus far (out of 101 turtles with known sex determination), 27 with a characterized sex chromosome system (13 of those karyotypically). These sex chromosomes are varied in terms of the ancestral autosome they co-opted and thus in their homology, as well as in their size (some are macro-, some are micro-chromosomes), heterogamety (some are XX/XY, some ZZ/ZW), dimorphism (some are virtually homomorphic, some heteromorphic with larger-X, larger W, or smaller-Y), age (the oldest system could be ~195 My old and the youngest < 25 My old). Combined, all data indicate that turtles follow some tenets of classic theoretical models of sex chromosome evolution while countering others. Finally, although the study of dosage compensation and molecular divergence of turtle sex chromosomes has lagged behind research on other aspects of their evolution, this gap is rapidly decreasing with the acceleration of ongoing research and growing genomic resources in this group.

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Darolti, Iulia, Alison E. Wright, Benjamin A. Sandkam, Jake Morris, Natasha I. Bloch, Marta Farré, Rebecca C. Fuller, et al. "Extreme heterogeneity in sex chromosome differentiation and dosage compensation in livebearers." Proceedings of the National Academy of Sciences 116, no. 38 (September 4, 2019): 19031–36. http://dx.doi.org/10.1073/pnas.1905298116.

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Once recombination is halted between the X and Y chromosomes, sex chromosomes begin to differentiate and transition to heteromorphism. While there is a remarkable variation across clades in the degree of sex chromosome divergence, far less is known about the variation in sex chromosome differentiation within clades. Here, we combined whole-genome and transcriptome sequencing data to characterize the structure and conservation of sex chromosome systems across Poeciliidae, the livebearing clade that includes guppies. We found that the Poecilia reticulata XY system is much older than previously thought, being shared not only with its sister species, Poecilia wingei, but also with Poecilia picta, which diverged roughly 20 million years ago. Despite the shared ancestry, we uncovered an extreme heterogeneity across these species in the proportion of the sex chromosome with suppressed recombination, and the degree of Y chromosome decay. The sex chromosomes in P. reticulata and P. wingei are largely homomorphic, with recombination in the former persisting over a substantial fraction. However, the sex chromosomes in P. picta are completely nonrecombining and strikingly heteromorphic. Remarkably, the profound degradation of the ancestral Y chromosome in P. picta is counterbalanced by the evolution of functional chromosome-wide dosage compensation in this species, which has not been previously observed in teleost fish. Our results offer important insight into the initial stages of sex chromosome evolution and dosage compensation.

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Marchi, A., and K. S. Rai. "Chromosome banding homologies in three species of Aedes (Stegomyia)." Canadian Journal of Genetics and Cytology 28, no. 2 (April 1, 1986): 198–202. http://dx.doi.org/10.1139/g86-027.

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The chromosome complements of the mosquitoes Aedes aegypti, Aedes mascarensis, and Aedes albopictus, belonging to the subgenus Stegomyia, gave a uniform response to the Q-, H-, and R-banding techniques. Of the three homomorphic chromosome pairs, only the shortest or sex pair (I) showed a consistent banding pattern. In the three species, a bright yellow intercalary band was present on one arm of both chromosomes of the sex pair after heat treatment and staining with acridine orange. The rest of the chromosome and the other two pairs fluoresced orange–red. The same intercalary region appeared completely dark with the fluorochromes quinacrine and Hoechst 33258, while the rest of the chromosomes fluoresced dull. The same banding pattern was present in males and females. Size variations of the Q- and H-negative and R-positive intercalary bands were observed within each species. The results are interpreted in terms of structural homology of the sex-determining chromosomes, which is retained within the subgenus.Key words: sex-determining chromosomes, banding (Q, H, R), Aedes, mosquitoes.

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Sember, Alexandr, Michaela Pappová, Martin Forman, Petr Nguyen, František Marec, Martina Dalíková, Klára Divišová, et al. "Patterns of Sex Chromosome Differentiation in Spiders: Insights from Comparative Genomic Hybridisation." Genes 11, no. 8 (July 24, 2020): 849. http://dx.doi.org/10.3390/genes11080849.

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Spiders are an intriguing model to analyse sex chromosome evolution because of their peculiar multiple X chromosome systems. Y chromosomes were considered rare in this group, arising after neo-sex chromosome formation by X chromosome-autosome rearrangements. However, recent findings suggest that Y chromosomes are more common in spiders than previously thought. Besides neo-sex chromosomes, they are also involved in the ancient X1X2Y system of haplogyne spiders, whose origin is unknown. Furthermore, spiders seem to exhibit obligatorily one or two pairs of cryptic homomorphic XY chromosomes (further cryptic sex chromosome pairs, CSCPs), which could represent the ancestral spider sex chromosomes. Here, we analyse the molecular differentiation of particular types of spider Y chromosomes in a representative set of ten species by comparative genomic hybridisation (CGH). We found a high Y chromosome differentiation in haplogyne species with X1X2Y system except for Loxosceles spp. CSCP chromosomes exhibited generally low differentiation. Possible mechanisms and factors behind the observed patterns are discussed. The presence of autosomal regions marked predominantly or exclusively with the male or female probe was also recorded. We attribute this pattern to intraspecific variability in the copy number and distribution of certain repetitive DNAs in spider genomes, pointing thus to the limits of CGH in this arachnid group. In addition, we confirmed nonrandom association of chromosomes belonging to particular CSCPs at spermatogonial mitosis and spermatocyte meiosis and their association with multiple Xs throughout meiosis. Taken together, our data suggest diverse evolutionary pathways of molecular differentiation in different types of spider Y chromosomes.

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Vicoso, B., V. B. Kaiser, and D. Bachtrog. "Sex-biased gene expression at homomorphic sex chromosomes in emus and its implication for sex chromosome evolution." Proceedings of the National Academy of Sciences 110, no. 16 (April 1, 2013): 6453–58. http://dx.doi.org/10.1073/pnas.1217027110.

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Mezzasalma, Marcello, Fabio M. Guarino, and Gaetano Odierna. "Lizards as Model Organisms of Sex Chromosome Evolution: What We Really Know from a Systematic Distribution of Available Data?" Genes 12, no. 9 (August 28, 2021): 1341. http://dx.doi.org/10.3390/genes12091341.

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Lizards represent unique model organisms in the study of sex determination and sex chromosome evolution. Among tetrapods, they are characterized by an unparalleled diversity of sex determination systems, including temperature-dependent sex determination (TSD) and genetic sex determination (GSD) under either male or female heterogamety. Sex chromosome systems are also extremely variable in lizards. They include simple (XY and ZW) and multiple (X1X2Y and Z1Z2W) sex chromosome systems and encompass all the different hypothesized stages of diversification of heterogametic chromosomes, from homomorphic to heteromorphic and completely heterochromatic sex chromosomes. The co-occurrence of TSD, GSD and different sex chromosome systems also characterizes different lizard taxa, which represent ideal models to study the emergence and the evolutionary drivers of sex reversal and sex chromosome turnover. In this review, we present a synthesis of general genome and karyotype features of non-snakes squamates and discuss the main theories and evidences on the evolution and diversification of their different sex determination and sex chromosome systems. We here provide a systematic assessment of the available data on lizard sex chromosome systems and an overview of the main cytogenetic and molecular methods used for their identification, using a qualitative and quantitative approach.

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Xu, Luohao, Simon Yung Wa Sin, Phil Grayson, Scott V. Edwards, and Timothy B. Sackton. "Evolutionary Dynamics of Sex Chromosomes of Paleognathous Birds." Genome Biology and Evolution 11, no. 8 (July 22, 2019): 2376–90. http://dx.doi.org/10.1093/gbe/evz154.

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Abstract Standard models of sex chromosome evolution propose that recombination suppression leads to the degeneration of the heterogametic chromosome, as is seen for the Y chromosome in mammals and the W chromosome in most birds. Unlike other birds, paleognaths (ratites and tinamous) possess large nondegenerate regions on their sex chromosomes (PARs or pseudoautosomal regions). It remains unclear why these large PARs are retained over >100 Myr, and how this retention impacts the evolution of sex chromosomes within this system. To address this puzzle, we analyzed Z chromosome evolution and gene expression across 12 paleognaths, several of whose genomes have recently been sequenced. We confirm at the genomic level that most paleognaths retain large PARs. As in other birds, we find that all paleognaths have incomplete dosage compensation on the regions of the Z chromosome homologous to degenerated portions of the W (differentiated regions), but we find no evidence for enrichments of male-biased genes in PARs. We find limited evidence for increased evolutionary rates (faster-Z) either across the chromosome or in differentiated regions for most paleognaths with large PARs, but do recover signals of faster-Z evolution in tinamou species with mostly degenerated W chromosomes, similar to the pattern seen in neognaths. Unexpectedly, in some species, PAR-linked genes evolve faster on average than genes on autosomes, suggested by diverse genomic features to be due to reduced efficacy of selection in paleognath PARs. Our analysis shows that paleognath Z chromosomes are atypical at the genomic level, but the evolutionary forces maintaining largely homomorphic sex chromosomes in these species remain elusive.

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Odierna, Gaetano, Augusto Gentilli, Marco Zuffi, and Gennaro Aprea. "The karyology of Vipera aspis, V. atra, V. hugyi, and Cerastes vipera." Amphibia-Reptilia 27, no. 1 (2006): 113–19. http://dx.doi.org/10.1163/156853806776052209.

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AbstractIn the current paper we show the results obtained using standard and banding staining methods (Ag-NOR-, CMA3-, C-banding and sequential colorations (or Alu I digestions) + CMA3 + DAPI) in specimens of Cerastes vipera, Vipera aspis, V. atra, and V. hugyi. Cerastes vipera presented chromosomal characters, primitive in snakes, as a karyotype of 2n = 36 chromosomes, with 16 biarmed macrochromosomes and 20 microchromosomes, NORs on one microchromosome pair and absence of cytologically evident sex chromosomes, at least with the methods used. The three taxa of Vipera studied showed chromosomal characters either derived, or primitive or at an initial stage of differentiation. All three species showed a karyotype (derived) of 2n = 42 chromosomes with 22 macro- and 20 micro-chromosomes; they all showed NORs on one micro-chromosome pair and presented Z and W chromosomes at an initial stage of differentiation. Sexchromosomes Z and W, were in fact homomorphic, but the former was near all euchromatic, while the W chromosome was almost completely heterochromatic. All the three taxa of Vipera resulted, however, karyologically diversified, mainly due to the number of macro-chromosomes pairs with a centromeric, CMA3 positive heterochromatin: almost all the pairs in V. aspis, two pairs in V. atra and absent in V. hugyi.

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Sousa, Aretuza, Jörg Fuchs, and Susanne S. Renner. "Cytogenetic comparison of heteromorphic and homomorphic sex chromosomes in Coccinia (Cucurbitaceae) points to sex chromosome turnover." Chromosome Research 25, no. 2 (March 25, 2017): 191–200. http://dx.doi.org/10.1007/s10577-017-9555-y.

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Kuhl, Heiner, Yann Guiguen, Christin Höhne, Eva Kreuz, Kang Du, Christophe Klopp, Céline Lopez-Roques, et al. "A 180 Myr-old female-specific genome region in sturgeon reveals the oldest known vertebrate sex determining system with undifferentiated sex chromosomes." Philosophical Transactions of the Royal Society B: Biological Sciences 376, no. 1832 (July 12, 2021): 20200089. http://dx.doi.org/10.1098/rstb.2020.0089.

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Several hypotheses explain the prevalence of undifferentiated sex chromosomes in poikilothermic vertebrates. Turnovers change the master sex determination gene, the sex chromosome or the sex determination system (e.g. XY to WZ). Jumping master genes stay main triggers but translocate to other chromosomes. Occasional recombination (e.g. in sex-reversed females) prevents sex chromosome degeneration. Recent research has uncovered conserved heteromorphic or even homomorphic sex chromosomes in several clades of non-avian and non-mammalian vertebrates. Sex determination in sturgeons (Acipenseridae) has been a long-standing basic biological question, linked to economical demands by the caviar-producing aquaculture. Here, we report the discovery of a sex-specific sequence from sterlet ( Acipenser ruthenus ). Using chromosome-scale assemblies and pool-sequencing, we first identified an approximately 16 kb female-specific region. We developed a PCR-genotyping test, yielding female-specific products in six species, spanning the entire phylogeny with the most divergent extant lineages ( A. sturio, A. oxyrinchus versus A. ruthenus, Huso huso ), stemming from an ancient tetraploidization. Similar results were obtained in two octoploid species ( A. gueldenstaedtii, A. baerii ). Conservation of a female-specific sequence for a long period, representing 180 Myr of sturgeon evolution, and across at least one polyploidization event, raises many interesting biological questions. We discuss a conserved undifferentiated sex chromosome system with a ZZ/ZW-mode of sex determination and potential alternatives. This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part I)’.

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Ogata, M., H. Ohtani, T. Igarashi, Y. Hasegawa, Y. Ichikawa, and I. Miura. "Change of the Heterogametic Sex From Male to Female in the Frog." Genetics 164, no. 2 (June 1, 2003): 613–20. http://dx.doi.org/10.1093/genetics/164.2.613.

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Abstract Two different types of sex chromosomes, XX/XY and ZZ/ZW, exist in the Japanese frog Rana rugosa. They are separated in two local forms that share a common origin in hybridization between the other two forms (West Japan and Kanto) with male heterogametic sex determination and homomorphic sex chromosomes. In this study, to find out how the different types of sex chromosomes differentiated, particularly the evolutionary reason for the heterogametic sex change from male to female, we performed artificial crossings between the West Japan and Kanto forms and mitochondrial 12S rRNA gene sequence analysis. The crossing results showed male bias using mother frogs with West Japan cytoplasm and female bias using those with Kanto cytoplasm. The mitochondrial genes of ZZ/ZW and XX/XY forms, respectively, were similar in sequence to those of the West Japan and Kanto forms. These results suggest that in the primary ZZ/ZW form, the West Japan strain was maternal and thus male bias was caused by the introgression of the Kanto strain while in the primary XX/XY form and vice versa. We therefore hypothesize that sex ratio bias according to the maternal origin of the hybrid population was a trigger for the sex chromosome differentiation and the change of heterogametic sex.

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Brelsford, Alan, Guillaume Lavanchy, Roberto Sermier, Anna Rausch, and Nicolas Perrin. "Identifying homomorphic sex chromosomes from wild-caught adults with limited genomic resources." Molecular Ecology Resources 17, no. 4 (November 18, 2016): 752–59. http://dx.doi.org/10.1111/1755-0998.12624.

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Volobouev, Vitaly, and Georges Pasteur. "Presumptive sex chromosomes of a unisexual homomorphic species of lizards, Lepidodactylus lugubris." Heredity 60, no. 3 (June 1, 1988): 463–67. http://dx.doi.org/10.1038/hdy.1988.65.

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Veltsos, Paris, Kate E. Ridout, Melissa A. Toups, Santiago C. González-Martínez, Aline Muyle, Olivier Emery, Pasi Rastas, et al. "Early Sex-Chromosome Evolution in the Diploid Dioecious Plant Mercurialis annua." Genetics 212, no. 3 (May 21, 2019): 815–35. http://dx.doi.org/10.1534/genetics.119.302045.

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Suppressed recombination allows divergence between homologous sex chromosomes and the functionality of their genes. Here, we reveal patterns of the earliest stages of sex-chromosome evolution in the diploid dioecious herb Mercurialis annua on the basis of cytological analysis, de novo genome assembly and annotation, genetic mapping, exome resequencing of natural populations, and transcriptome analysis. The genome assembly contained 34,105 expressed genes, of which 10,076 were assigned to linkage groups. Genetic mapping and exome resequencing of individuals across the species range both identified the largest linkage group, LG1, as the sex chromosome. Although the sex chromosomes of M. annua are karyotypically homomorphic, we estimate that about one-third of the Y chromosome, containing 568 transcripts and spanning 22.3 cM in the corresponding female map, has ceased recombining. Nevertheless, we found limited evidence for Y-chromosome degeneration in terms of gene loss and pseudogenization, and most X- and Y-linked genes appear to have diverged in the period subsequent to speciation between M. annua and its sister species M. huetii, which shares the same sex-determining region. Taken together, our results suggest that the M. annua Y chromosome has at least two evolutionary strata: a small old stratum shared with M. huetii, and a more recent larger stratum that is probably unique to M. annua and that stopped recombining ∼1 MYA. Patterns of gene expression within the nonrecombining region are consistent with the idea that sexually antagonistic selection may have played a role in favoring suppressed recombination.

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Fujito, Satoshi, Satoshi Takahata, Reimi Suzuki, Yoichiro Hoshino, Nobuko Ohmido, and Yasuyuki Onodera. "Evidence for a Common Origin of Homomorphic and Heteromorphic Sex Chromosomes in DistinctSpinaciaSpecies." G3: Genes|Genomes|Genetics 5, no. 8 (June 5, 2015): 1663–73. http://dx.doi.org/10.1534/g3.115.018671.

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Fontaine, Albin, Igor Filipović, Thanyalak Fansiri, Ary A. Hoffmann, Changde Cheng, Mark Kirkpatrick, Gordana Rašić, and Louis Lambrechts. "Extensive Genetic Differentiation between Homomorphic Sex Chromosomes in the Mosquito Vector, Aedes aegypti." Genome Biology and Evolution 9, no. 9 (September 1, 2017): 2322–35. http://dx.doi.org/10.1093/gbe/evx171.

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Dwarka, Arvin, Cynthia M. Ross Friedman, Mairi E. MacKay, and Don Nelson. "Polymerase chain reaction identification of a female-specific genetic marker in Arceuthobium americanum (lodgepole pine dwarf mistletoe) and its implications for Arceuthobium sex determination." Botany 89, no. 6 (June 2011): 369–77. http://dx.doi.org/10.1139/b11-025.

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In North America, the most widespread and speciose mistletoe is Arceuthobium M. Bieb. (dwarf mistletoes, Viscaceae), which is a dioecious parasite of conifers. Little is known about its sex determination system, and sex chromosomes have not been identified. A genetic marker for early gender discrimination in Arceuthobium would be useful in the study of sex ratios and sex determination. Here, random amplified polymorphic DNA analysis via the polymerase chain reaction (PCR) was used to investigate genetic differences between genders in Arceuthobium americanum Nutt. ex Engelm. collected near Kamloops, British Columbia and Bélair, Manitoba. A total of 196 10-mer primers were selected for analysis of DNA from isolated male and female A. americanum somatic tissue. A ∼900 bp female-specific DNA fragment was generated with primer OPB-18 (5′-CCACAGCAGT-3′). The fragment was cloned and sequenced. Using GenBank and the basic local alignment search tool alignment software, it was determined that the first ∼300 bp of this DNA sequence shared a high degree of similarity to transposable elements (76%) and a Y-chromosome (male) fragment (75%) in Silene latifolia Poir. Sequence-characterized amplified region primers were then designed. This study has generated an efficient molecular tool to differentiate male and female A. americanum while also providing evidence indicating that A. americanum may have homomorphic, possibly protoheteromorphic, sex chromosomes.

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Yazdi, Homa Papoli, and Hans Ellegren. "Old but Not (So) Degenerated—Slow Evolution of Largely Homomorphic Sex Chromosomes in Ratites." Molecular Biology and Evolution 31, no. 6 (March 10, 2014): 1444–53. http://dx.doi.org/10.1093/molbev/msu101.

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OYAMA, R. K., S. M. VOLZ, and S. S. RENNER. "A sex-linked SCAR marker in Bryonia dioica (Cucurbitaceae), a dioecious species with XY sex-determination and homomorphic sex chromosomes." Journal of Evolutionary Biology 22, no. 1 (January 2009): 214–24. http://dx.doi.org/10.1111/j.1420-9101.2008.01641.x.

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Traut, Walther, and Brigitte Wollert. "An X/Y DNA segment from an early stage of sex chromosome differentiation in the fly Megaselia scalaris." Genome 41, no. 2 (April 1, 1998): 289–94. http://dx.doi.org/10.1139/g98-015.

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The sex chromosomes of the Megaselia scalaris wild-type strain Wien are homomorphic. We studied a roughly 1.8 kb X/Y DNA segment of this strain. It includes, at one end, the first part of a coding sequence for a protein of the vespid antigen 5 family. Molecular differentiation between the X and Y chromosomes has commenced, but homology, even of short DNA stretches, is still assessable beyond doubt. The most conspicuous differences between the X and the homologous Y segment were insertions/deletions in the noncoding region: among them, deletions, a duplication, and an insertion of a mobile element. These structural changes grossly disrupted homology. In comparison, base substitutions, though more numerous, contributed little to the differentiation of the X/Y DNA segment.Key words: sex determination, molecular differentiation, mobile element, vespid antigen 5.

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Veltsos, Paris, Guillaume Cossard, Emmanuel Beaudoing, Genséric Beydon, Dessislava Savova Bianchi, Camille Roux, Santiago C. González-Martínez, and John R. Pannell. "Size and Content of the Sex-Determining Region of the Y Chromosome in Dioecious Mercurialis annua, a Plant with Homomorphic Sex Chromosomes." Genes 9, no. 6 (May 29, 2018): 277. http://dx.doi.org/10.3390/genes9060277.

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Roco, Álvaro S., Adrián Ruiz-García, and Mónica Bullejos. "Testis Development and Differentiation in Amphibians." Genes 12, no. 4 (April 16, 2021): 578. http://dx.doi.org/10.3390/genes12040578.

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Sex is determined genetically in amphibians; however, little is known about the sex chromosomes, testis-determining genes, and the genes involved in testis differentiation in this class. Certain inherent characteristics of the species of this group, like the homomorphic sex chromosomes, the high diversity of the sex-determining mechanisms, or the existence of polyploids, may hinder the design of experiments when studying how the gonads can differentiate. Even so, other features, like their external development or the possibility of inducing sex reversal by external treatments, can be helpful. This review summarizes the current knowledge on amphibian sex determination, gonadal development, and testis differentiation. The analysis of this information, compared with the information available for other vertebrate groups, allows us to identify the evolutionarily conserved and divergent pathways involved in testis differentiation. Overall, the data confirm the previous observations in other vertebrates—the morphology of the adult testis is similar across different groups; however, the male-determining signal and the genetic networks involved in testis differentiation are not evolutionarily conserved.

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de Oliveira Furo, Ivanete, Rafael Kretschmer, Michelly S. dos Santos, Carlos A. de Lima Carvalho, Ricardo J. Gunski, Patrícia C. M. O'Brien, Malcolm A. Ferguson-Smith, Marcelo B. Cioffi, and Edivaldo H. C. de Oliveira. "Chromosomal Mapping of Repetitive DNAs in Myiopsitta monachus and Amazona aestiva (Psittaciformes, Psittacidae) with Emphasis on the Sex Chromosomes." Cytogenetic and Genome Research 151, no. 3 (2017): 151–60. http://dx.doi.org/10.1159/000464458.

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Here, for the first time, we describe the karyotype of Myiopsitta monachus (Psittacidae, Arini). We found 2n = 48, corresponding to the lowest diploid number observed in Neotropical Psittaciformes so far, with an uncommonly large W chromosome homomorphic to the Z. In order to better understand the evolution of the sex chromosomes in this species, we applied several molecular cytogenetic approaches, including C-banding, FISH mapping of repetitive DNAs (several microsatellite repeats), and whole-chromosome painting on metaphases of M. monachus. For comparison, another species belonging to the same tribe but with a smaller W chromosome (A. aestiva) was also analyzed. The results show that the constitutive heterochromatin has a very diverse distribution pattern in these species revealing heterochromatic blocks in the centromeric region of all chromosomes and in most of the length of the W chromosome in A. aestiva, while in M. monachus they were found in interstitial and telomeric regions. Concerning the microsatellites, only the sequence (CG)n produced signals on the W chromosome of A. aestiva, in the distal region of both arms. However, in M. monachus, (CAA)n, (CAG)n, and (CG)n probes were accumulated on the W chromosome, and, in addition, the sequence (CAG)n also hybridized to heterochromatic regions in macrochromosomes, as well as in microchromosomes. Based on these results, we suggest that the increase in length of the W chromosome in M. monachus is due to the amplification of repetitive elements, which highlights their significant role in the evolutionary process of sex chromosome differentiation.

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Willhoeft, Ute, and Walther Traut. "Molecular differentiation of the homomorphic sex chromosomes inMegaselia scalaris (Diptera) detected by random DNA probes." Chromosoma 99, no. 4 (August 1990): 237–42. http://dx.doi.org/10.1007/bf01731698.

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Cornetti, Luca, and Dieter Ebert. "No evidence for genetic sex determination in Daphnia magna." Royal Society Open Science 8, no. 6 (June 2021): 202292. http://dx.doi.org/10.1098/rsos.202292.

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Mechanisms of sex determination (SD) differ widely across the tree of life. In genotypic sex determination (GSD), genetic elements determine whether individuals are male or female, while in environmental sex determination (ESD), external cues control the sex of the offspring. In cyclical parthenogens, females produce mostly asexual daughters, but environmental stimuli such as crowding, temperature or photoperiod may cause them to produce sons. In aphids, sons are induced by ESD, even though GSD is present, with females carrying two X chromosomes and males only one (X0 SD system). By contrast, although ESD exists in Daphnia , the two sexes were suggested to be genetically identical, based on a 1972 study on Daphnia magna (2n=20) that used three allozyme markers. This study cannot, however, rule out an X0 system, as all three markers may be located on autosomes. Motivated by the life cycle similarities of Daphnia and aphids, and the absence of karyotype information for Daphnia males, we tested for GSD (homomorphic sex chromosomes and X0) systems in D. magna using a whole-genome approach by comparing males and females of three genotypes. Our results confirm the absence of haploid chromosomes or haploid genomic regions in D. magna males as well as the absence of sex-linked genomic regions and sex-specific single-nucleotide polymorphisms. Within the limitations of the three studied populations here and the methods used, we suggest that our results make the possibility of genetic differences among sexes in the widely used Daphnia model system very unlikely.

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Suárez-Villota, Elkin Y., José C. Pansonato-Alves, Fausto Foresti, and Milton H. Gallardo. "Homomorphic Sex Chromosomes and the Intriguing Y Chromosome of Ctenomys Rodent Species (Rodentia, Ctenomyidae)." Cytogenetic and Genome Research 143, no. 4 (2014): 232–40. http://dx.doi.org/10.1159/000366173.

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Ruiz-García, Adrián, Álvaro S. Roco, and Mónica Bullejos. "Sex Differentiation in Amphibians: Effect of Temperature and Its Influence on Sex Reversal." Sexual Development 15, no. 1-3 (2021): 157–67. http://dx.doi.org/10.1159/000515220.

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The role of environmental factors in sexual differentiation in amphibians is not new. The effect of hormones or hormone-like compounds is widely demonstrated. However, the effect of temperature has traditionally been regarded as something anecdotal that occurs in extreme situations and not as a factor to be considered. The data currently available reveal a different situation. Sexual differentiation in some amphibian species can be altered even by small changes in temperature. On the other hand, although not proven, it is possible that temperature is related to the appearance of sex-reversed individuals in natural populations under conditions unrelated to environmental contaminants. According to this, temperature, through sex reversal (phenotypic sex opposed to genetic sex), could play an important role in the turnover of sex-determining genes and in the maintenance of homomorphic sex chromosomes in this group. Accordingly, and given the expected increase in global temperatures, growth and sexual differentiation in amphibians could easily be affected, altering the sex ratio in natural populations and posing major conservation challenges for a group in worldwide decline. It is therefore particularly urgent to understand the mechanism by which temperature affects sexual differentiation in amphibians.

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Ma, Wen-Juan, Paris Veltsos, Melissa Toups, Nicolas Rodrigues, Roberto Sermier, Daniel Jeffries, and Nicolas Perrin. "Tissue Specificity and Dynamics of Sex-Biased Gene Expression in a Common Frog Population with Differentiated, Yet Homomorphic, Sex Chromosomes." Genes 9, no. 6 (June 12, 2018): 294. http://dx.doi.org/10.3390/genes9060294.

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Tennessen, Jacob A., Rajanikanth Govindarajulu, Aaron Liston, and Tia‐Lynn Ashman. "Homomorphic ZW chromosomes in a wild strawberry show distinctive recombination heterogeneity but a small sex‐determining region." New Phytologist 211, no. 4 (April 22, 2016): 1412–23. http://dx.doi.org/10.1111/nph.13983.

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Ogawa, A., K. Murata, and S. Mizuno. "The location of Z- and W-linked marker genes and sequence on the homomorphic sex chromosomes of the ostrich and the emu." Proceedings of the National Academy of Sciences 95, no. 8 (April 14, 1998): 4415–18. http://dx.doi.org/10.1073/pnas.95.8.4415.

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Stöck, M., R. Savary, C. Betto-Colliard, S. Biollay, H. Jourdan-Pineau, and N. Perrin. "Low rates of X-Y recombination, not turnovers, account for homomorphic sex chromosomes in several diploid species of Palearctic green toads (Bufo viridis subgroup)." Journal of Evolutionary Biology 26, no. 3 (January 14, 2013): 674–82. http://dx.doi.org/10.1111/jeb.12086.

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Darolti, Iulia, Alison E. Wright, and Judith E. Mank. "Guppy Y Chromosome Integrity Maintained by Incomplete Recombination Suppression." Genome Biology and Evolution 12, no. 6 (May 19, 2020): 965–77. http://dx.doi.org/10.1093/gbe/evaa099.

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Abstract The loss of recombination triggers divergence between the sex chromosomes and promotes degeneration of the sex-limited chromosome. Several livebearers within the genus Poecilia share a male-heterogametic sex chromosome system that is roughly 20 Myr old, with extreme variation in the degree of Y chromosome divergence. In Poecilia picta, the Y is highly degenerate and associated with complete X chromosome dosage compensation. In contrast, although recombination is restricted across almost the entire length of the sex chromosomes in Poecilia reticulata and Poecilia wingei, divergence between the X chromosome and the Y chromosome is very low. This clade therefore offers a unique opportunity to study the forces that accelerate or hinder sex chromosome divergence. We used RNA-seq data from multiple families of both P. reticulata and P. wingei, the species with low levels of sex chromosome divergence, to differentiate X and Y coding sequences based on sex-limited SNP inheritance. Phylogenetic tree analyses reveal that occasional recombination has persisted between the sex chromosomes for much of their length, as X- and Y-linked sequences cluster by species instead of by gametolog. This incomplete recombination suppression maintains the extensive homomorphy observed in these systems. In addition, we see differences between the previously identified strata in the phylogenetic clustering of X–Y orthologs, with those that cluster by chromosome located in the older stratum, the region previously associated with the sex-determining locus. However, recombination arrest appears to have expanded throughout the sex chromosomes more gradually instead of through a stepwise process associated with inversions.

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Hartmann, Fanny E., and Wen‐Juan Ma. "Digest: Climate plays marginal role for homomorphic sex chromosome differentiation in common frogs†." Evolution 74, no. 3 (February 3, 2020): 690–93. http://dx.doi.org/10.1111/evo.13936.

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Furman, Benjamin L. S., and Ben J. Evans. "Divergent Evolutionary Trajectories of Two Young, Homomorphic, and Closely Related Sex Chromosome Systems." Genome Biology and Evolution 10, no. 3 (February 21, 2018): 742–55. http://dx.doi.org/10.1093/gbe/evy045.

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Arribas, Oscar, and Gaetano Odierna. "Karyological and osteological data supporting the specific status of Iberolacerta (cyreni) martinezricai (Arribas, 1996)." Amphibia-Reptilia 25, no. 4 (2004): 359–67. http://dx.doi.org/10.1163/1568538042788942.

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AbstractIberolacerta (cyreni) martinezricai has a karyotype of 2n = 36, all acrocentric macrochromosomes. Nucleolar Organizer Regions (NORs) are interstitially situated on a medium small (MS-type) chromosome, a derived character shared with I. cyreni, which differs in details of W-sex chromosome: W is heteromorphic and heterochromatic in I. cyreni, while it is homomorphic and euchromatic in I. (c.) martinezricai. Osteologically, it is characterized by the presence of a triangular-shaped expansion of the squamosal towards the supratemporal fenestra, and by the presence of seven (instead of six) posterior short ribbed presacral vertebrae. These odd characters probably became fixed in this relic taxon by imbreeding. Its differences and affinities are discussed, proposing a specific status for this taxon.

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Journal articles on the topic 'Homomorphic sex chromosomes'

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