Selective maintenance of recombination between the sex chromosomes

Abstract

A hallmark of many sex chromosomes is the dramatically reduced rate of recombination between them in the heterogametic sex (e.g. between the X and Y). Sexually antagonistic selection is thought to be the main selective driver of this reduced recombination, with tighter linkage strengthening the association between alleles favourable to females and the X, as well as alleles favourable to males and the Y. Nevertheless, many sex chromosomes retain substantial levels of recombination over millions of years, and some old sex chromosomes remain homomorphic with few signs of recombination suppression and the chromosomal degradation expected to follow. This paper explores the selective factors that can maintain recombination between the sex chromosomes. Specifically, by analysing the dynamics of genes that modify the rate of recombination, I present results demonstrating that certain forms of selection -all involving overdominance in males -can positively maintain recombination in the pseudo-autosomal region. To understand these cases, one has to revise our standard view of sexual antagonistic selection as involving two partners (males and females) to three partners (the X in females, the X in males and the Y).

Sex uncovered: the evolutionary biology of reproductive systems

“…However, within‐locus associations may also have important effects on selection for sex and recombination in diploid organisms (e.g. Otto, ; Roze & Lenormand, ; Agrawal, ; Roze & Michod, ), whereas the paper by Otto in the present volume shows that overdominant selection may alter classical predictions on the evolution of recombination on sex chromosomes. Conversely, Kamran‐Disfani & Agrawal () show that selection for recombination may maintain low rates of outcrossing within predominantly selfing populations.…”

Evolutionary dynamics of sex chromosomes of paleognathous birds

“…Classic views on the evolution of sex chromosomes argue that recombination suppression ultimately leads to the complete degeneration of the sex-limited chromosomes (Charlesworth et al 2005;Bachtrog 2006). However, recent theoretical work suggests suppression of recombination is not always favored, and may require strong sexually antagonistic selection or other conditions (Otto 2014). Thus, there may be conditions which would have driven tight linkage of the sex-determining locus and sex-specific beneficial loci via the suppression of recombination in neognaths (Gorelick et al 2016;Charlesworth 2017), but not in paleognaths, although the exact model that could produce this pattern remains unclear, given that it would require, for example, fewer sexually antagonistic mutations in paleognaths than in neognaths.…”

ZZ/ZW Sex Chromosomes in the Endemic Puerto Rican Leaf-Toed Gecko (<b><i>Phyllodactylus wirshingi</i></b>)

“…2011; Otto, 2014]. Furthermore, such data do not address which chromosomes in the genome are the sex chromosomes in a comparative framework.…”