The Pseudoallelism of White and Apricot in Drosophila Melanogaster.

In summary it can be stated that in Bx' the sy)+, Bx+, fu+ loci as well as x, a locus to the right of fu+, are duplicated'. The classical example of multiple allelism is the series of eye-color mutants at the white (w) locus in Drosophila melanogaster. The altemative interpretation of this series, namely, that it is made up of "pseudoalleles," or closely linked genes with similar effects, has usually been considered ruled out by two kinds of evidence. In the first place early attempts to resolve the series by crossing over failed in spite of numerous tests involving most of the mutants available at the time.1-4 Secondly, a heterozy-gote for two different mutant genes of the series does not have the pheno type expected for non-allelic genes, namely, wild-type (or red) eye color, but instead has a mutant eye color which is usually intermediate between the colors of the two respective homozygotes. In recent years, however, several cases have been found in which non-allelic genes give a positive phenotypic test for allelism by virtue of a position effect.-'7 In such cases, which have been termed "position pseudoalleles,"7 mutant genes at the different loci (say, a and b) give a mutant phenotype in the a +/+ b heterozygote, but a wild-type, or more nearly wild-type, phenotype in the a b/+ + heterozygote. With the above considerations in mind and with the aid of more adequate techniques for studying crossing over than were available in the early studies, the white gene and its so-called "allele," apricot, have been rein-vestigated. This paper presenos the evidence that these two genes occupy separate loci and that they constitute another example of position pseudo-allelism. In what follows, the apricot gene, formerly symbolized as wa will be designated by a new symbol, namely, apr. In order to investigate the possibility of crossing over between w and apr, females with attached-X chromosomes were employed so that the two complementary products from any such crossing over 'would sometimes be recoverable simultaneously in a single individual. The first step was the