Polymorphism and uniparental inheritance of mitochondrial DNA in Physarum polycephalum

Restriction endonuclease analysis was done on mitochondrial DNA (mtDNA) from 19 plasmodial strains of Physarum polycephalum. The extent of mtDNA variation among these strains was high in comparison with other organisms, and provides a useful source of cytoplasmic genetic markers. The strains were classified into seven groups according to their mtDNA types. Although plasmodia of P. polycephalum are diploid, formed by fusion of amoebal isogametes, each of the 19 plasmodia possessed mtDNA of only a single type. The transmission pattern of mtDNA during plasmodium formation was studied by mating pairs of amoebal strains that contained mtDNA of different types. Transmission was uniparental; the plasmodia that were formed carried mtDNA with the restriction pattern of only one of the two parental types. Since diploid zygotes develop into plasmodia by repeated mitotic cycles in the absence of cell division, it is clear that this uniparental transmission of mtDNA does not depend upon random partitioning either of mitochondria or of mtDNA molecules during cell division.