Frequencies of sex determination factors in Italian housefly populations

The housefly (Musca domestica L.) has a remarkable polymorphic sex determination system. It consists of various male and female determining genes with different alleles. Allelic frequencies of male and female determiners follow a latitudinal cline but can differ remarkably between populations. The male determining locus (M) can be present on the Y, X or any of the five autosomes. A dominant female determiner (WZ-system) is also found in some populations. In 2025, we resampled populations around Bologna (Italy) that were previously investigated in 1982 and 2006. Using back crosses and linkage analysis with strains carrying recessive visible mutations, we established hemizygosity and homozygosity of M factors, their chromosomal location and population frequencies. Presence of the dominant female determiner was determined by PCR. We compare the 2025 distribution of variants with the earlier samples to see whether population frequencies remained stable or shifted.