Index >> Multiple Alleles >> Example of Pseudoallelism

All of these genes are located at about 1.5 on the X chromosome map. However, in crosses that originally produced only apricot and white progeny, about 1 in 10,000 individuals had wild type red eyes. By using certain techniques of chromosome mapping, i.e., by using the “marker gene" y for yellow body colour at locus 1.0 and spl (split bristles) at locus 3.0, it was possible to show that gene for apricot and white occupied separate, but extremely close, loci with a crossover frequency of approximately 0.01.

Surprisingly, the two possible kinds of heterozygous females turn out to have different phenotypes. Thus, ww⁺/w⁺ w^ap is pale apricot, and w⁺w⁺/ww^ap is wild type. If the wild type alleles (w⁺w⁺) are in the cis position (i.e., w⁺w⁺/w w^ap), red eyes occur, if they are in the trans configuration (i.e., w⁺w⁺/w^ap w⁺), the phenotype is pale apricot (mutant).