Semi-Allelic Genes

Abstract

The semiallelic genes are a group of genes with similar phenotypic effect, located on the chromosome in direct sequence. Crossing over, if any, occurs between them with very low frequency. They may be distinguished from the true allelic genes by the mosaic appearance of the characters and the covering effect in the heterozygote. They differ from the ordinary linked genes in the similarity of their phenotypes and in the complete or nearly complete absence of recombination. Semiallelic genes are rather common, and are widely distr. in various animals and man. Many examples are presented from among mutant genes in Drosophila, other insects, vertebrate animals, and man. It is possible that A-B, M-N-S, and Rh[degree]-Rh''-Rh" blood-type genes also belong to the semiallelic group.