Centromeres may explain suppressed recombination in sex chromosome evolution

Recent genome sequences lend support to a long-debated idea in sex chromosome evolution: the extensive sex-linked regions seen in some species may not require any active recombination suppression process at all. Instead, according to a review by Deborah Charlesworth published in PLOS Genetics, the sex-determining locus may simply sit near a centromere, where the well-known “centromere effect” keeps recombination rates low.

Centromere-proximal regions of chromosomes recombine rarely as a general property of genomes. If a sex-determining gene lies in or near such a pericentromeric region, the surrounding stretch of DNA can become sex-linked without invoking any special evolutionary mechanism. On this view, debates about which types of selection might drive the spread of recombination suppression become unnecessary, because the low recombination is a pre-existing feature of the genome region itself.

The review outlines the properties of genome regions that recombine rarely, including pericentromeric regions, and examines sex-linked regions that overlap with them. Charlesworth notes that it is difficult to distinguish special features of such sex-linked regions that would indicate they have undergone an active recombination suppression process. One property most likely to be specific to completely sex-linked regions is major gene loss from Y- or W-linked regions of genes that are still present in their X- or Z-linked counterparts, an asymmetry observed in many species.

However, if pericentromeric regions are characterised by ephemeral gene content and low gene expression, asymmetry between the sex chromosomes in pericentromeric sex-linked regions might be less pronounced than in sex-linked regions elsewhere in the genome. The review reports that similar levels of Y and X degeneration are indeed documented in several species, consistent with this expectation. In addition, some sex-linked regions overlapping pericentromeres may not be completely sex-linked, which could explain findings of extensive sex-linked regions showing low Y-X or W-Z divergence. The work suggests that where a sex-determining locus lies near a centromere, genome geography alone may shape the evolution of sex chromosomes.

Subject of Research: The role of pericentromeric genome regions and the centromere effect in sex chromosome evolution

Article Title: The peculiar properties of pericentromeric regions of genomes and their influence on sex chromosome evolution

Article References: Charlesworth, D. (2026). The peculiar properties of pericentromeric regions of genomes and their influence on sex chromosome evolution. PLOS Genetics, 22(10), e1012333. https://doi.org/10.1371/journal.pgen.1012333

Image Credits: AI Generated

DOI: 10.1371/journal.pgen.1012333

Keywords: sex chromosomes, pericentromeric regions, centromere effect, recombination suppression, sex-linked regions, Y chromosome degeneration, genome evolution, PLOS Genetics, Deborah Charlesworth, Y-X divergence, peculiar, properties