Dictyate Oocytes of a Kangaroo (Macropus robustus) Show Paternal Inactivation at the X-linked Gpd Locus

Purified samples of large numbers of dictyate oocytes from 13 M. robustus pouch young heterozygous for glucose-6-phosphate dehydrogenase type and six homozygous controls were examined electrophoretically to determine activity states at the Gpd locus. Like somatic cortical and medullary cells, oocytes expressed only the maternal phenotype irrespective of the direction of the cross. No evidence was found of reactivation of the inactive (paternal) allele or inactivation of both maternal and paternal alleles. It was therefore concluded that unlike eutherian dictyate oocytes, only a single (maternal) allele is active in each dictyate oocyte in M. robustus. The stage of reactivation of the paternal allele remains to be determined.