Phenotypes Recognizable in the Progeny of Axolotl Parents Both Heterozygous for the Same Two Mutant Genes

Abstract

SYNOPSIS. A survey has been made of the types of progeny in fourteen groups of axolotl spawnings from parents both heterozygous for the same two mutant genes. For none of the parental types did the progeny homozygous for both mutant genes constitute a distinct phenotype as did the rrlxx larvae recently described by Humphrey and Chung (1977) from matings of parents both heterozygous for genes r and x. In four of the fourteen types of matings some few double homozygotes were recognizable by the fact that the gene pair dominating the development of their morphological type had failed to prevent theappearance of one particular feature resulting from the action of the second gene pair. In spawnings from parents with the other ten gene combinations no double homozygotes were recognized. In many of these, the excess number of mutants of one of the two expected types indicated that the double homozygotes had been identified as being of that type. It is concluded that in the majority of matings in which double homozygotes are expected, the mutant gene whose influence on development begins earliest determines the visible pattern of morphology and also the approximate life span of the double homozygote. The latter sometimes dies before the stage at which features determined by its second gene pair are due to appear. Only when the two pairs of mutant genes act more or less simultaneously and in a cumulative fashion is the double homozygote likely to appear as a phenotype distinctly different from the two usual mutant types included among its siblings.