Strict paternal transmission of mitochondrial DNA of Chlamydomonas species is explained by selection against maternal nucleoids.

The non-Mendelian inheritance of organelle DNA is common in most plants and animals. Here we examined inheritance mechanisms involved in the transfer of mitochondrial DNA. We successively backcrossed (to F(5)) two interfertile strains of the unicellular isogamous haploid algae Chlamydomonas reinhardtii and Chlamydomonas smithii to match nuclear backgrounds and examine transmission patterns of mitochondrial DNA by PCR analysis of cob gene sequences. Mitochondrial DNA was strictly transmitted paternally. To investigate the behavior of parental mitochondrial DNA, we used F(5) progeny to form zygotes and isolated single zygotes. The results showed selective disappearance of maternal mitochondrial nucleoids occurred between 3 and 6 h after zygote formation.