Character Changes Caused by Mutation of an Entire Region of a Chromosome in Drosophila.

A female, just hatched, having wings serrated or notched at the end, was found in the purple stock bottle, October 7, 1918. In order to test whether this character was due to a new mutation the female was mated to males from an unrelated stock. The majority of her few F, daughters had typically “notch” wings quite like the females in the old stocks called notch (see MORGAN and BRIDGES 1916). Later crosses in which larger numbers were obtained always gave notch females, normal females, and normal males in equal numbers, but no notch males, showing that the mutant was a sex-linked dominant, acting in addition as a lethal in the male, precisely like the old notch. It was possible to ascertain that the purple stock had not been contaminated. The character was accordingly considered as due to a reappearance of the old notch gene. Notch was known to have reappeared six times since it first occurred. In order to find out whether the location of the new notch ( “notch,”) gene was identical with that of the earlier ones, two cultures were raised in which a red-eyed notch, female was crossed to males carrying the sex-linked recessive genes eosin (eye color) and crimson (eye color). These genes are located fairly near to the left and to the right respectively of the old notch gene. When the F, flies hatched, a paradoxical result was obtained: All the notch, daughters, instead of being red-eyed as expected, had a yellowish eosin-like eye color. Since the normal-winged daughters did not show this exceptional eye color, the latter could not be due to a duplication of the eosin gene in the X chromosome received from the eosin crimson fathers, and it was at once regarded as probable that the appearance of F, eosin notch females was due to a “deficiency” (BRIDGES 1917) in the 1 From the Zoological Laboratory of COLUMBIA UNIVERSITY.