Causes and consequences of reciprocal translocations on sex chromosomes

Abstract

Under XY sex determination, the Y chromosome is only inherited via males, whereas the X chromosome is predominantly found in females. Thus, it is favourable when alleles with high male fitness become associated with the Y chromosome and when alleles with high female fitness become associated with the X chromosome. These favourable associations can be strengthened through linkage. Rearrangements, such as inversions and sex chromosome–autosome fusions, can increase linkage and thereby become favoured (Charlesworth, 2017). In a From the Cover article in this issue of Molecular Ecology, Toups, Rodrigues, Perrin, and Kirkpatrick (2019) present the first genomic analysis of a sex chromosome reciprocal translocation, a particularly dramatic chromosomal rearrangement that modifies linkage with the sex chromosome. As a result of reciprocal translocation, one studied population of the common frog (Rana temporaria, Figure 1) displays a remarkable sex‐determining system in which there are two physically unlinked sex chromosomes that are exclusively cotransmitted (Figure 2a).

Rapid turnover and evolution of sex-determining regions amongSebastesrockfishes

“…The fact that the sex association signal reaches one end of each chromosome supports that there is a chromosomal translocation that joins these regions. There are examples in nature of large-scale chromosomal rearrangements leading to novel sex chromosomes, including sex chromosome fusions in stickleback (Sardell et al, 2021) and a reciprocal translocation in common frogs, which resulted in two physically separate but coinherited sex chromosomes (Scott, 2019). A third explanation may be found in Chinook salmon, in whom the sex-determining locus is readily translocated between two chromosomes (McKinney et al, 2020).…”

Rapid turnover and evolution of sex‐determining regions in Sebastes rockfishes

“…The fact that the sex association signal reaches one end of each chromosome supports that there is a chromosomal translocation that joins these regions. There are examples in nature of large‐scale chromosomal rearrangements leading to novel sex chromosomes, including sex chromosome fusions in stickleback (Sardell et al, 2021) and a reciprocal translocation in common frogs, which resulted in two physically separate but coinherited sex chromosomes (Scott, 2019). Given the lack of a chromosome scale reference genome for this species, we cannot say if the translocation was involved in the formation of the sex chromosome or whether an ancestral translocation in this species was then co‐opted by a sex determining region but we consider the first to be more parsimonious.…”