Preferential segregation of the fourth chromosomes in Drosophila melanogaster

The present study is concerned chiefly with the behavior of a duplicating chromosome derived from the undescribed scute allelomorph known as scute-10-2. This allelomorph, obtained by x-raying scute-10, is associated with a reciprocal 1-4 translocation. The X-chromosome is broken near its left end, between the loci of silver and broad, and the short terminal piece (loci from yellow to silver) is exchanged for a section of the fourth chromosome that includes all the known loci of that chromosome (with the possible exception of cubitus-interruptus, which is difficult to test, since this translocation shows the position effect recently described by Dubinin and Sidoroff(1)). The small chromosome, made up of the left end of X attached to the spindle-fibre region of 4, may be obtained in individuals (of either sex) that are otherwise normal diploids.(2) If the normal X's of such hyperploids carry the recessive gene for yellow, the flies are wild-type in appearance because of the presence of +y in the duplicating chromosome. This fact has been used, in the present experiments, to study the distribution of the fragment at meiosis.