Genetics of inbred Drosophila melanogaster : XVII. Changes in the cytoplasm related to the length of the generation interval

L üning , K.G. 1987. Genetics of inbred Drosophila melanogaster . XVII. Changes in the cytoplasm related to the length of the generation interval. ‐ Hereditas 106: 107–113. Lund, Sweden. ISSN 0018–0661. Received May 2, 1986 A common genome “Karsnäs”, code “K”, was by back‐crossing introduced into cytoplasm from seven different iso‐female lines. Two or four sister‐lines were started from each. They were propagated with 14‐day generation intervals. After more than 20 generations of back‐crossing, sublines were branched off and were propagated at 2May generation intervals by sampling offspring from the 15–17th day of egg‐laying. Five of the seven sets of sublines had a changed norm of reaction as regards the frequency of X0 males in the two or four sister‐lines. In one cytoplasm only had one of the two sublines changed after 14 generations and in another cytoplasm none had changed after nine generations. We have shown here that it was the change in the generation interval that caused the change of norm of reaction. By repeating the tests at the 27th and 22nd generation, respectively, we found that all sublines had changed more or less. From one suhline which had changed less we established 17 suh‐suhlines from single females. These fell into two (possibly three) groups as regards the frequencies of X0 males. One group showed the original norm of reaction typical of a short generation interval. This result indicates that the change of reaction is discontinuous rather than gradual. Some consequences are discussed.