September 2019 Cover Image

Picture of a female house fly, Musca domestica. House fly is a model species for studying polygenic sex determination. Male-determining genes have been found on all six house fly chromosomes, and a dominant female determining gene is also present in some populations. This means that any chromosome in the house fly genome can be a sex chromosome. This natural variation appears to be maintained by natural selection, despite the fact that the X and Y chromosome pairs have very similar DNA sequence content. Image courtesy of Peter Koomen. See Son et al. in GENETICS 213: 313–327.