Gene Duplication and the Genome Distribution of Sex-Biased Genes

Abstract

In species that have two sexes, a single genome encodes two morphs, as each sex can be thought of as a distinct morph. This means that the same set of genes are differentially expressed in the different sexes. Many questions emanate from this statement. What proportion of genes contributes to sexual dimorphism? How do they contribute to sexual dimorphism? How is sex-biased expression achieved? Which sex and what tissues contribute the most to sex-biased expression? Do sex-biased genes have the same evolutionary patterns as nonbiased genes? We review the current data on sex-biased expression in species with heteromorphic sex chromosomes and comment on the most important hypotheses suggested to explain the origin, evolution, and distribution patterns of sex-biased genes. In this perspective we emphasize how gene duplication serves as an important molecular mechanism to resolve genomic clashes and genetic conflicts by generating sex-biased genes, often sex-specific genes, and contributes greatly to the underlying genetic basis of sexual dimorphism.

Sequential Turnovers of Sex Chromosomes in African Clawed Frogs (Xenopus) Suggest Some Genomic Regions Are Good at Sex Determination

“…More information about the nature of the master trigger for sex determination in X. borealis , on sex-linked genes, and on sex-biased expression of genes elsewhere in the genome may cast additional light on the drivers of sex chromosome turnover in these frogs. The drivers could include the role of alternative mechanisms that could resolve sexual conflict, such as gene duplication (Gallach et al 2011; Wyman et al 2012), which is a potentially important factor in these tetraploid species.…”

Male Sexual Development and the Androgenic Gland: Novel Insights through the de novo Assembled Transcriptome of the Eastern Spiny Lobster,<b><i> Sagmariasus verreauxi</i></b>

“…As is seen with S. verreauxi , this male bias is often most pronounced in the testis [Meiklejohn et al, 2003;Ellegren and Parsch, 2007;Ingleby et al, 2014], with tissues such as the brain showing minimal sex bias [Ingleby et al, 2014]. It has been suggested that the phenomenon of male-biased expression is due to the rapid divergence and subsequent evolution of male genes in respect to both sequence and expression, ultimately owing to the fact that male genes are under less selective constraint [Ellegren and Parsch, 2007;Gallach et al, 2011;Parsch and Ellegren, 2013;Stuglik et al, 2014]. In Medaka (Oryzias latipes) the inhibitory action of the male sex determinant Dmrt1bY (DMY) supports the classical view that in at least XX/XY mechanisms, female sex determination appears to be the default pathway [Saito et al, 2007].…”

Male-Biased Genes in Catfish as Revealed by RNA-Seq Analysis of the Testis Transcriptome

“…In such cases, male and female genomes carry identical or almost identical DNA. It is possible that the subtle differences of a very small portion of genes located on sex-specific chromosomes or sex-determining region are responsible for the sex determination [20]–[22], and discovery of the Y-specific sequences may be difficult. In the extreme situation under this case like in the case of Fugu, there are no Y-specific sequences or Y-specific transcripts.…”