Emergence of Genetic Sex Determination in an Environmentally Sex-Determined Animal

. This process has led to the emergence of a mixed-mating system, in which sex determination is jointly regulated by genetic and environmental factors, with ongoing divergence in chromosomal structure continuing to develop between the two haplotypes at the population level. These findings suggest that processes analogous to early sex-chromosome evolution are occurring in this ESD species, offering insights into the molecular mechanisms underlying the emergence of GSD.