Abstract
Second chromosomes have been found in natural populations of Drosophiln nzelanognster that contain an abnormal centromere region which conditions a highly aberrant segregation ratio in heterozygous males (Sandler, Hiraizumi, and Sandler, 1959). In particular, when a chromosome carrying this abnornlal region (symbolized SD for Segregation-distorter) is made heterozygous with a normal second chronlosome (routinely a standard tester chronlosome inarlted by the recessives cyz and bw) in males, and bacltcrossed to homozygous C17 bw females, 90 per cent or more of the F1 receive the SD-bearing second chromosome. These abnormal segregation ratios are not accompanied by egg mortality. It has now ,been found that as heterozygous SD males are aged, the segregation ratios become less abnormal. When, moreover, young sons of awed ? fathers are examined, it is found that they too exhibit less extreme segregation ratios. Indeed, changes in the segregation ratio induced by aging may persist in selected ,males for at least five generations and possibly indefinitely. T h e evidence demonstrating a heritable aging effect and a consideration of certain other questions relevant to the aging phenonlenon are presented below.
Published Version
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