De novo mutation-like events observed at the 6PGD locus of the Japanese quail, and the principle of polymorphism breeding more polymorphism.

Abstract

In our stock of Japanese quail, four alleles which specify electrophoretic variants A, B, C, and D of an enzyme, 6PGD, are maintained. Analysis of the progeny from a mating which should have produced only known types of heterozygotes enabled us to detect a great variety of mutation-like events which affected the germ cells of the parents. A total of 1011 progeny from 26 such matings were typed for their 6PGD phenotype. Eleven showed unexpected phenotypes, some of which were apparent products of deletions or duplications. Thus, it appeared that the spontaneous rate of occurrence of all the mutation-like events per 6PGD locus per generation approaches 1×10−2 in Japanese quail. All 11 mutation-like events occurred in the heterozygous parents. Furthermore, 8 of the 11 parents were A/D heterozygotes. A and D show the greatest difference in their electrophoretic mobility, which suggests that two variant subunits differ by several amino acid substitutions rather than by a single amino acid substitution. Of the 11 unexpected progeny, three received new, hitherto nonexistent electrophoretic variants from one of the parents. Perhaps there is a principle that mutation-like events are more likely to occur in germ cells of the parent which is heterozygous for extremely different alleles. This would imply that the new electrophoretic variants presently observed were produced by intracistronic recombination.