Figure 4.

Raw phototaxis data obtained following X-ray mutagenesis.

The X-rayed parent males were mated to virgin females of the attached-X stock. The F1 offspring of the above cross were tested by the “phototaxis box” (Fig. 3), and the F1 males remaining in the dark side tube (right side tube in Fig. 3) were single-male mated to virgin attached-X females. The results shown are those from the F2 offspring of this second cross, obtained on June 1 and 2, 1967. As may be seen, the phototaxis test fractionated the population of flies in each line according to their gender, almost all females going toward light and almost all males remaining in the dark. The results were consistent with the supposition that mutations induced on the X-chromosome caused the impairment of phototaxis in males. In a similar fashion, three other presumptive non-phototactic lines were isolated a week or two later.