Search

The stock of Nasonia vitripennis marked by the nuclear eye color mutation "tinged" (ti) shows nonreciprocal cytoplasmic incompatibility with wild-type (+) strains. Homogenates prepared from ti female pupae and injected into + female pupae caused 39% of the recipients to acquire the incompatibility characteristics of the ti donors. When eggs obtained from ti females were fragmented and injected into + female pupae, or when the ti egg cytoplasm was injected into chick eggs and yolk sac homogenates were subsequently injected into + female pupae, 28% of the recipients acquired ti-type incompatibility characteristics. Results from passage of the egg cytoplasm through 0.23-microns millipore filters showed successful transfer of the incompatibility and suggest that the incompatibility system in N. vitripennis has two components: a bacterium and a smaller agent.

Four stocks derived from aberrant segregation of R-locus genes in male progeny following incompatible crosses in Mormoniella have shown characteristics suggesting that genes found on added chromosomal fragments in these stocks have separated from each other. In most cases, this separation was associated with elevated temperatures at the time of and subsequent to fertilization. Data also suggest that the R-locus genes involved are adjacent to a centromere, with the O factor being proximal thereto.

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.