A Comparison Between the Position Effects of Normal and Mutant Alleles

Abstract

In Drosophila melanogaster heterozygotes between the mutant gene ci (cubitus interruptus) and a normal allele +2 or +c are mostly normal in phenotype. If a rearrangement has taken place near to the ci locus the heterozygotes show varying degrees of vein interruptions. This position effect is of different strength according to whether the rearrangement involves the chromosome with a normal allele, R( + ), or its homologue with the mutant allele, R(ci). While different position alleles of either type lead to different mean values for degree of expression, the distribution of means for 26 types of R(ci)/+ flies is significantly less extreme than for 19 types of R(+)/ci flies. The significance of these results on interpretations of position effects is indicated.