Weird Animal Genomes and the Evolution of Vertebrate Sex and Sex Chromosomes

Humans, mice, and even kangaroos have an X female:XX male system of sex determination, in which the Y harbors a male-dominant sex-determining gene SRY. Birds have the opposite, ZZ males and ZW females, and may use a dosage-sensitive Z-borne gene. Other reptiles have genetic sex but no visible sex chromosomes, or determine sex by temperature of egg incubation. How can we make sense of so much variation? Flow do systems change in evolution? Studies of some unlikely animals-platypus and dragon lizards, frogs and fish-confirm that evolutionary transitions have occurred between TSD anti GSD systems, between XY and ZW systems, anti even between male and female heterogametic systems. Here I explore nonmodel systems that offer some new perspectives on some venerable questions of sex and sex chromosomes.