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This sort of biparental egg protection in insects is rare.

Mitochondrial DNA was thought to derive exclusively from maternal egg cells, with no paternal contribution, but Luo et al. challenge this dogma, identifying three families with mtDNA heteroplasmy caused by biparental mitochondrial inheritance.

Although biparental inheritance of mtDNA and heteroplasmy coincided with disease symptoms in some of the individuals studied by Luo et al., the authors’ data do not demonstrate a causal link with disease.

The authors went on to identify two additional and unrelated families that had biparental mitochondrial transmission.

Together, these reports provide evidence for biparental mitochondrial inheritance in humans.