Fig. 1.

As paternal mtDNA (A) is distributed among blastomeres not all of them receive a copy (B). Later germline is parted from soma (C) and then the sex of the germline is set (D). After birth (dotted line), somatic and male germline cells exert selection in favor of the paternal mtDNA haplotype, so that somatic cells and spermatozoa end up as a paternal/maternal mtDNA mosaic. This explains somatic heteroplasmy (E) and quasi-Mendelian inheritance (F), respectively. In the female germline, there is no selection for the paternal haplotype (9), so oocytes keep low and variable proportions of paternal mtDNA (G) (SN7.3.2).