Genome exclusion in gametogenesis by an interspecific <i>Rana</i> hybrid: Evidence from electrophoresis of individual oocytes

Abstract

Abstract The diploid hybridogenetic frog Rana esculenta , an interspecific hybrid of R. ridibunda and R. lessonae , usually transmits its ridibunda genome to progeny: the lessonae genome is lost before gametogenesis is completed. Samples of ovary reveal only ridibunda alleles when examined electrophoretically. Cytological and genetic evidence suggests that the lessonae genome is excluded premeiotically. Since recombination between the parental genomes occurs at a low frequency, such recombination should be detectable by examination of the alleles expressed in individual enlarged oocytes. Examination of electrophoretic markers for four loci from 860 individual oocytes (100 each from eight females, ten each from six females) revealed no evidence of either heterozygosity or recombination, although the eight females for which 100 oocytes were examined were somatically heterozygous 29 times for these loci, so that there were 2,900 possibilities for detecting heterozygosity or recombination in the oocytes. These data abundantly confirm the inactivity of the lessonae genome during vitellogenesis in Rana esculenta . They are consistent with a premeiotic exclusion of the lessonae genome, but do not require it. The lessonae genome may be present although inactive, which may permit occasional crossing over between the lessonae and ridibunda genomes. The exclusion of the lessonae genome possibly is a consequence of its inactivity. Exclusion of the non‐ridibunda genome seems to be under control of loci located in the ridibunda genome. A regulatory endoduplication of the ridibunda genome may be necessary before an orderly meiosis can occur.