By back-crossing for twenty or more generations to males from an inbred line of Drosophila melanogaster we had produced sets of isogenic lines propagated with a short or a long generation interval respectively. The generation interval had been shown to have a profound influence on the effect on fecundity and chromosome loss in tested hybrids from these lines. By reverting the generation interval from long to short and vice versa we have shown that the sets of four sister lines reacted similarly but were influenced differently by the various sources of cytoplasm. Reverting the generation interval, starting from single females, showed that all lines successively reached the original level of reaction. These results suggest that successive changes may occur in the concentration (?) or activity of factors in the cytoplasm which had maintained their specificity for a great number of generations. Some consequences of cytoplasmic diversity are discussed.
展开▼
