A CASE OF POLYPLOIDY IN DIPTERA

Abstract

not a crossover was detected in a marked region including the q locus, and regardless of the direction of any such crossovers. For these reasons, and from a consideration of the relative frequency of niacin-independence in the various marker classes obtained , it was concluded that niacin-independence does not seem to be the result of crossing over in the usual sense. Nevertheless, increased crossing over in the marked region appeared to be associated with the occurrence of niacin-independence. The possibility has been discussed that various characteristics of the q mutants are occasioned by the insertion of chromosomal material at or near the region of the q locus. The repeated discovery of polyploidy in animals which show parthenogenesis, hermaphroditism, or vegetative reproduction and the rarity of its discovery in strictly bisexual forms have in a sense verified the prediction made by Muller' that the chromosome mechanism in many bisexual forms would tend to prevent the establishment of polyploid strains. Although apparent exceptions to this general prediction are known,2 still it seems clear that Muller's prediction holds to a large extent. In female-producing (thelytokous) parthenogenetic species no problem of 194 PROC. N. A. S.