Some Aspects of Position Pseudoallelism

The phenomenon of pseudoallelism promises to contribute much to our understanding of the gene—how it functions, how it mutates, how it evolves. The functional aspect will be the central theme of this paper. Attention will be focused chiefly on examples of “position pseudoallelism”; namely, those cases in which there is a position effect or phenotypic difference between the “cis-type” (a b/++) and “trans-type” (a+/+b ) of double mutant heterozygote. In most of these examples a close functional relationship between the adjoining loci is indicated.