A REMARKABLE ACTION OF THE MUTANT “RUDIMENTARY” IN Drosophila Melanogaster

Abstract

Females homo-zygous for the rudimentary alleles rPxbl and r6, if fertile, produce large numbers of wild-type daughters, a few such sons, and a few rudimentary daughters and sons. The + daughters are genetically +/r. The explanation is that only those eggs of rr female develop that are derived from r/+ nuclei in the rr ovary. These originate from the polar copulation nucleus of the grandmother r/+ which exceptionally entered the germ track. If these r/+ eggs develop by psuedoparthenogenesis (autogamy)[long dash]a possibility known from the moth Solenobla[long dash]the offspring are female and wild type. If occasionally a few such nuclei undergo normal meiosis and fertilization, the possible classes of daughters as well as sons appear in small and equal numbers. A repetition with the alleles r9 and r30 gave only a few such cases in about 8000 females tested; r30 females are almost sterile, r9 females relatively fertile. All together, about 1 female in 20 was fertile. In many of these, the grandmaternal X chromosome was marked with Bar, but only once were Bar offspring obtained from non-Bar rr female by the activation of the grandmaternal polar copulation nucleus. A few more such cases occurred with complications by previous crossing over, all together in less than 2% of the fertile females.