Contributions to the Knowledge of Non-Disjunction of the Sex-Chromosomes in Drosophila virilis
I. General Problems
1932 年 3 巻 4 号 p. 340-349
詳細
1932 年 3 巻 4 号 p. 340-349
(1) The frequency of primary exceptions in D. virilis is about 1:1000; that is somewhat higher than that in D. melanogaster (1:2000). The frequency of primary exceptional females is much lower than that of the males, being 1:15 in my experiment.
(2) The secondary exceptions are very rare as previous workers have pointed out, the frequency being only 0.53 per cent in my experiment.
(3) The non-disjunction was verified on cytological ground also. There are 3 longer rod-shaped, 2 shorter rod-shaped and one dot-like pairs of chromosomes in the normal oogonial metaphase. The X-chro-mosomes are probably one of these two shorter pairs. No difference in length is found between X and Y.
(4) Crossing-over in XXY females is not different from that in XX females.
(5) XX to XXY ratio among regular daughters of XXY females has been found to be about 5:3, instead of 1:1. Such an abnormal ratio can be easily accounted for by assuming that one of the sex chromosomes (X or Y) lags on the spindle and does not enter the nucleus of either of the two newly formed cells at the first maturation division.
