Paternal leakage of mitochondrial DNA in the great tit

The animal mitochondrial DNA is normally inherited clonally from mother to all her offspring. Mitochondrial heteroplasmy, the occurrence of more than one mitochondrial haplotype within an individual can be generated by relatively common somatic mutations within an individual, by heteroplasmy of the oocytes or by paternal leakage of mitochondria during the fertilization of an egg

Laura Kvist et al, Society for Molecular Biology and Evolution, 2003