Mapping and assembly of the Midas cichlid male-specific region supports molecular parallelism in the evolution of a master sex-determining role for amhr2

The evolution of sex chromosomes and their differentiation from autosomes is a major event during genome evolution that happened many times in several lineages. The repeated evolution and lability of sex-determination mechanisms in fishes makes this a well-suited system to test for general and predictable patterns in evolution. According to current theory, differentiation is triggered by the suppression of recombination following the evolution of a new master-sex determining gene. However, the molecular mechanisms that establish recombination suppression are known from few examples, owing to the intrinsic difficulties of assembling sex determining regions (SDRs). Forward-genetics data and the development of long-read sequencing have generated a wealth of data questioning central aspects of the current theory. Here, we demonstrate that sex in Midas cichlids is determined by an XY system, identify and assemble the SDR by combining forward-genetics, long-read sequencing and optical mapping...