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http://hdl.handle.net/11375/25163
Title: | The genomic architecture of sex-biased gene expression in Xenopus borealis |
Authors: | Song, Xue-Ying |
Advisor: | Evans, Ben |
Department: | Biology |
Keywords: | transcriptomic;RNAseq;evolution;frog;xenopus borealis;sex chromosome |
Publication Date: | 2019 |
Abstract: | Most vertebrates have separate sexes, and sex-specific traits that are regulated by genes with sex-biased expression patterns. In many species with genetic sex determination system, genetic recombination is suppressed in genomic regions linked to the master regulator of sex determination – the gene or set of linked loci that orchestrate sexual differentiation. Natural selection may favour alleles with sex-specific effects - including those with sexually antagonistic (SA) fitness effects (e.g., beneficial to females but harmful to males) – to become fixed in or be translocated to these non-recombining regions of sex chromosomes, because sex-specific or sex-biased modes of inheritance can resolve genomic conflict associated with SA. Sexually antagonism may also be resolve by sex-biased gene expression, and in theory these two mechanism (sex-linkage and sex-biased gene expression) could operate synergistically. However, there are relatively few empirical studies that test whether genes with sex biased expression patterns are indeed more abundant on sex chromosomes – and especially on newly evolved sex chromosomes. We explored this question with an African frog species Xenopus borealis, whose sex chromosome evolved within the last 25 million years (my) and have a large (~50Mbp) region of suppressed recombination, making it a young sex chromosome system compared to many other intensively studied systems, such as the sex chromosomes of mammals. We tested the possibility that a higher proportion of genes with sex-biased expression would be located on the sex-linked region of the sex chromosome of this species. By examining gene expression in adult liver and gonad and also tadpole gonad/mesenephros at two developmental stages, we found that the sex-linked region of these sex chromosome do have a higher proportion of sex biased genes compared to the non-sex-linked region of the same sex chromosomes, compared to (i) a homeologous genomic region in the tetraploid genome of X. borealis, and also (ii) the autosomes of this species. We did not observe the same pattern in a closely related frog species, Xenopus laevis, which has sex chromosome that are not homologous to those of X. borealis and, unlike X. borealis, lacks a large region of suppressed recombination on its sex chromosome. Using Brownian Motion model, we found as well that expression divergence evolution of genes in the sex-linked region of X. borealis is faster compared to its non-sex-linked homeologs (within X. borealis), and also compared to orthologous regions that are also non-sex-linked. One possible explanation for these observations is that natural selection favoured an expansion of recombination suppression (via unknown mechanisms) on chromosome such that polymorphic regulatory regions became linked (or unlinked) to the sex determining locus in such a way to resolve SA. Alternatively, it is possible that these sex-biased expression pattern evolved rapidly after recombination suppression. |
URI: | http://hdl.handle.net/11375/25163 |
Appears in Collections: | Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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Song_XueYing_Dec2019_MSC.pdf | 26.21 MB | Adobe PDF | View/Open |
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