Aberrant segregation of R-locus genes in male progeny from incompatible crosses in Mormoniella.

Crosses of females from Mormoniella stocks containing pe-333 type cross incompatibility with males from stocks lacking the incompatibility produced progeny that included 29 males with unexpected eye colors. Eight of these males gave rise to stocks that included some individuals with "speckled" eyes, containing sectors or spots of different colors. In these stocks there were unexpectedly low frequencies of transmission of the new phenotypes to progeny. Phenotypes, and results of crosses, are consistent with the hypothesis that the original males and the stocks that they sired contained extra bits of chromatin contributed by the sperm of the males used in the incompatible crosses. In these stocks, these pieces are transmitted with greater frequency by sperm than by eggs, and are occasionally lost in mitosis (producing "speckled" eyes). Data also indicate that the extra chromatin contains only the O and S factors, or the O factor alone, of the eye color locus R. Examination of spermatogonia shows an extra piece of chromatin in cells of males with phenotypes that suggest the presence of such a piece. The piece has not been found in spermatogonia of controls.