Synchronous activation of both parental alleles at the 6-PGD locus of Japanese quail embryos

The gene locus for the enzyme 6-phosphogluconate dehydrogenase belongs to that part of the genome which is activated at the beginning of embryonic development. The present experiment, utilizing three alleles at this autosomally inherited locus of the Japanese quail, was designed to show whether exhaustion of maternally stored 6-PGD is followed by maternally hemizygous de novo synthesis of the same enzyme. 6-PGD phenotypes of early embryos resulting from the mating between a male homozygous for one allele and a female heterozygous for two other alleles were examined by starch gel electrophoresis. The result showed that the maternally stored 6-PGD is exhausted before the twenty-fourth hour of incubation. This is followed by synchronous activation of both parental alleles. Previous studies on the development of various interspecific crosses have revealed that, at all loci studied, the activation of the maternally derived allele preceded that of the paternally derived allele. The present experiment reveals that preferential activation of maternally derived alleles need not be a rule of development.This work was supported in part by a grant (CA-05138) from the National Cancer Institute, U.S. Public Health Service, and in part by a research fund established in honor of General James H. Doolittle. Contribution No. 6-68, Department of Biology, City of Hope Medical Center.