Sex-chromosome segregation in inbred Drosophila melanogaster XXY females. I. Influence of closely related Y chromosome derivatives.

In tests of XXYder hybrids from two inbred lines of Drosophila melanogaster, a non-random distribution of various Yder chromosomes was found at regular X disjunction. This non-random Yder distribution was dependent on differences within the proximal X chromosome region (forked--centromere) of these particular lines, with a limited influence of the Yder,s. The Yder,s (originating from BsYy+ chromosome) showed a large influence on both level and brood pattern of secondary non-disjunction. There was no correlation between secondary non-disjunction and non-random Yder distribution, indicating different mechanisms. Cytological examination of the five Yder chromosomes disclosed no relation between the composition or configuration of the Yder,s and the observed distribution effects. Various parts of the present results show inconsistencies with either of the two existing segregation models (Grell, Novitski), suggesting that the mechanistic understanding of the meiotic process requires additional assumptions and/or alternatives.