Divergent evolution of male-determining loci on proto-Y chromosomes of the housefly.

Houseflies provide a good experimental model to study the initial evolutionary stages of a primary sex-determining locus because they possess different recently evolved proto-Y chromosomes that contain male-determining loci (M) with the same male-determining gene, Mdmd. We investigate M-loci genomically and cytogenetically revealing distinct molecular architectures among M-loci. M on chromosome V (M) has two intact Mdmd copies in a palindrome.