MODIFICATION OF ABNORMAL GAMETIC RATIOS INDROSOPHILA. III. PROBABLE TIME OF THE,A-TYPE EFFECT IN BAR-STONE TRANSLOCATION MALES

Abstract

Bar-Stone translocation males of Drosophila melanogaster possess, as one pair of homologues, a fourth chromosome attached to a large distal piece of the X chromosome (xD) and a normal fourth chromosome (IV), and as another pair, the proximal piece of the X chromosome (XP) and the Y chromosome (Y). When raised at a normal temperature, i. e., about 26[degree]C, the so-called A-type Bar-Stone males give highly distorted segregation ratios; the ratio XD: IV is about 0. 4 : 0. 6, and the ratio XP: Y is about 0. 67 : 0. 33. However, when A-type males are raised at 18[degree]C (and tested at 26[degree]C), normal (equal) ratios are found (Zimmering, 1960). This finding provided a means of determining the probable stage at which the A-effect takes place. The method employed consisted of raising, at 18[degree]C, A-type males which were in successively older developmental stages of their life cycle, and correlating the disappearance of distorted ratios with the types of germ cells present after the time of removal to the cooler temperature. The results suggest a meiotic phenomenon.