Evolution of a Y Chromosome from an X Chromosome
84 Pages Posted: 11 Jul 2019 Publication Status: Review Complete
More...Abstract
Turnovers of sex chromosomes — where an ancestral sex-determining region is replaced by a new one, or moves to a new genomic location, often on a different chromosome — have rarely been studied within a phylogenetic context that allows the ancestral states to be inferred. Here we compare three closely related species of the fish genus Poecilia, P. reticulata (the guppy), P. picta and P. parae, which reveals that the guppy Y chromosome evolved from an ancestral X chromosome, the first documented case of an X chromosome evolving to become a new Y chromosome. We show that the sex determining locus in all three species is carried on the same chromosome, chromosome 12 in P. reticulata. However, whereas the guppy Y chromosome retains essentially all genes found on the X chromosome, P. picta’s Y chromosome has lost most of them, and is highly degenerated. The few X-linked genes that have retained detectable Y copies in P. picta are almost all homologues of guppy pseudo-autosomal genes. Microsatellite genotyping shows that P. parae also has a degenerated Y chromosome. The guppy Y chromosome must therefore have evolved from an ancestral X chromosome after the split from P. picta and P. parae. Another close relative, the platyfish, must also descend from the same ancestor with a highly degenerated Y chromosome, and its sex chromosome pair is an autosome in both the guppy and P. picta. This evidence for repeated and independent changes supports a role for genetic degeneration in sex chromosome turnovers.
Keywords: Genetic degeneration, sex chromosome turnover, Poecilia, Micropoecilia, heterochiasmy, high-throughput genotyping
Suggested Citation: Suggested Citation