Heteroplasmy suggests limited biparental inheritance of Mytilus mitochondrial DNA.

Strict maternal inheritance of mitochondrial DNA is commonly observed in animals. There is usually only one mitochondrial DNA population (homoplasmy) within an individual. Mussels of the Mytilus edulis species group appear to be exceptions in both respects. Of 150 Mytilus individuals examined, 85 were heteroplasmic. Mitochondrial DNA types within heteroplasmic individuals differed greatly; in one comparison, the inferred sequence difference was 20 +/- 5 percent. Homoplasmic individuals with mitochondrial DNA similar to the heteroplasmic mitochondrial DNA types were found. These observations are best explained by the hypothesis that biparental inheritance of mitochondrial DNA can occur in Mytilus.