Gametic selection affecting sex‐ratio in housefly(Musca domesticaL.)

An inheritable mechanism of sex‐ratio distortion, causing a conspicuous, variable and unpredictable excess of males, has been recently observed in a field population of Musca domestica. The cause of this sex‐ratio distortion, named Non‐Mendelian‐Sex‐Ratio (NMSR), is always strictly associated with a male determinant on autosome 3 (M III). NMRS causes a gametic selection, whereby the sperms carrying NMSR are advantaged during zygote formation. Therefore, the progeny consists mainly of males due to the association with M III. Moreover, absence of crossing‐over has been ascertained in females heterozygous for morphological markers of autosome 3 and carrying M III and NMSR. This lack of recombination among NMSR, M III and the markers of autosome 3 suggests that NMSR might be a true gene (NMSR), or the result of the pleiotropic gene action of a new M III (M III‐NMSR).