Abstract
The validity of the use of the term "pseudo-alleles" to designate closely linked genes with similar effects is considered. The term "pseudo-allelism" was employed originally by Bridges to describe a positive test for allelism between neighboring but dissimilar mutant genes and several dominant vestigial mutations which proved to be deficiencies. In view of its prior use in this special sense the term pseudo-alleles is not an appropriate designation for those rapidly accumulating cases of genes whose close linkage and similar effects suggest their origin through duplication. For these the term "para-alleles" is suggested.