The relationship between first and second chromosome segregation ratios from Drosophila melanogaster males bearing Segregation Distorter

Summary Drosophila melanogaster males heterozygous for the second chromosome locus Segregation Distorter preferentially transmit this chromosome to their progeny due to a dysfunctioning of SD ⁺-bearing sperm. SD males with a normal sex chromosome constitution produce more females than males among SD ⁺ progeny. This report shows that this unequal recovery of sexes is enhanced from XY/Y; SD/SD ⁺ males and enhanced still further from XY/O; SD/SD ⁺ males. It is argued that the probability that a SD ⁺-bearing sperm will dysfunction is related to its sex chromsome complement, with the relative probabilities of dysfunction ranked O> Y> X> XY. It is shown that a modified probit analysis accounts for the relationship between sex ratio and second chromosome segregation frequency for all paternal genotypes. Finally, SD/SD ⁺ males show no increase in sex chromosome nondisjunction with respect to a control.R. E. Denell was supported by U.S.P.H.S. Training Grant No. GM00337 and by a U.S.P.H.S. Postdoctoral Fellowship; George L. Gabor Miklos was supported by A.E.C. Contract No. AT (04-3)-34 PA150.