A genetic study of the effects of the repair-deficient mei-9a mutation in Drosophila on spontaneous and X-ray-induced paternal sex chromosome loss.

The repair-deficient mutant, mei-9a in Drosophila melanogaster was investigated regarding its effect on spontaneous and X-ray-induced chromosome loss in male postmeiotic cells. From matings of males carrying a mei-9a or an ordinary ring-X and a doubly marked Y chromosome (BSYy+) with mei-9a or ordinary females, the spontaneous frequencies of complete loss, partial loss, and inferred ring-X loss (based on shifts in sex ratio female:male) were significantly higher with mei-9a than with non-mei-9a. When males were given 3000 rad X-irradiation, frequencies of induced partial loss, inferred ring-X loss and the reduction in the number of progeny per female were significantly greater with mei-9a than with non-mei-9a. The results provide evidence that the mei-9a is a potentiator of both spontaneous and X-ray-induced chromosome lesions in sperm of the Drosophila male. Evidence is presented which implicates the presence of mei-9a in the P1 female and not the male as (at least) largely responsible for the characteristic mei-9a effects.