[Expression of homologous genes in interspecies arctic fox x silver fox hybrids (Alopex lagopus X Vulpes vulpes). III. Mechanisms of expression of alleles of locus GPD, located on the X-chromosome].

The electrophoretic pattern of glucose-6-phosphate dehydrogenase (G-6-PD) was studied in 60 intergeneric fox hybrids (Alopex lagopus X Vulpes vulpes), 33 females and 27 males. It is shown that the structural gene for G-6-PD, designated as Gpd, is located on the X-chromosome in both Arctic and silver foxes. Analysis of G-6-PD in the erythrocytes of hybrid females demonstrated that the phenotypic expression of parental alleles at the locus Gpd varied considerably: from 1:1 to the hemizygous manisfestation of an allele of either the Arctic or silver fox. It is suggested that the variable quantitative expression of the alleles at the locus Gpd in hybrid females is related to the presence of two cell populations having in an active state either the X-chromosome of the Artic or silver fox. It is also assumed that the size of two cell populations is significantly influenced by the different relations in the group of initiator (stem) cells, which possess different X-chromosomes in an active state, which has been established in early embryogenesis. In the case of erythrocytes, it is found that the number of initiator (stem) cells for erythrocytes comprises 5-6.