Some Observations on the Structure of the Scute-8 Chromosome of Drosophila Melanogaster.

We have been interested in the structure of the X chromosome of the stock known as scute-8 apricot, found by SIDOROV (1931). This stock has been used extensively in our laboratory, and it early became a matter of importance to have exact information on the nature of this chromosome, It was of course known that it contained a long inversion, but its exact limits had not been fully worked out. The fact that the locus of bobbed was inverted was shown in 1932 (PATTERSON 193213, p. 154), and a diagram of the scute-8 apricot chromosome, based on all of the evidence then available, was &dished in 1933 (PATTERSON 1933, p. 34). In this diagram it was indicated that the inverted section extends from a point lying just to the right of the locus of scute (scute-8), to some point lying between the locus of bobbed and the fiber-bearing end of the chromosome. The genes in the inverted section appear in reverse order, with the locus of bobbed lying near to that of yellow, and followed by the loci of such genes as carnation, forked, garnet, and so on, to white, finally ending with the so-called gene for viability (PATTERSON 1932a). We now have evidence which shows that the left-hand break occurred between achaete and scute, so that the locus of scute-8 is also inverted. In a paper dealing with mosaic formation (PATTERSON 1933) experiments were described in which scute-8 apricot flies had been X-rayed and mated to untreated yellow white crossveinless miniature forked3 flies. Among the F1 flies were found 146 yellow apricot hypoploid females, the so-called aberrant females. These were interpreted as having resulted from the breaking off and elimination of the left end of the treated scute-8 chromosome, thus creating a deficiency at the locus of yellow. If the locus of bobbed is inverted and lies near to that of yellow, then a certain percentage of these yellow aberrant females should also be deficient a t the bobbed locus. In order to determine this point, 61 of these yellow females were tested to echinus forked bobbed males. The results show that eight of the 61 were also deficient for bobbed, as indicated by the appearance of bobbed females among their off spring. The conclusion to be drawn from this test is that the locus of bobbed lies near to that of yellow, and is therefore involved in the inversion. The fact that 53 of the 61 females tested to bobbed showed that the