Sex determination of the onion fly,Hylemya antiqua (Meigen)

In testes of many XXY₂ and XXY₂Y₂ males of Hylemya antiqua a numerical variation for Y₂, a consequence of mitotic nondisjunction, has been established. In 22 of 79 progenies of XXY₂ (including some unidentified XXY₂Y₂) males the ratio of females to males was significantly (p<0.05) different from 11, 9 with excess females and 13 with excess males. It could be concluded, firstly, that in progenies of XXY₂ males sex ratio distortion results from a numerical variation of Y₂ between the primordial germ cells of the male parent and secondly, that probably at least three primordial germ cells are involved in the formation of the male germ cells of the onion fly. Besides, the occurrence of some highly distorted sex ratios in male direction could be attributed to the presence of XXY₂Y₂ males. The frequency of M II cells with 2 Y₂ chromosomes established in XXY₂ males amounted to 2.9%. In XXY₂Y₂ males this percentage was higher and occasionally M IIs with 3 Y₂ were found. In the progeny of one cross a chromosome morphologically identical with Y₂ but lacking its holandric inheritance was found. From its inheritance, it could be concluded that it was a nonfunctional (mutated) Y₂ chromosome (Y_m). Interesting phenomena were the reduced transmission of Y_m through the female, and the observation of very high numbers of Y_m in some ovarian cells. A possible causal relationship between these two phenomena is discussed.