The Song of the Cell: An Exploration of Medicine and the New Human

by Siddhartha Mukherjee

Mitochondrial mutations are special because they can be inherited only from your mother, while most other mutations can come from either parent. Mitochondria don’t have an autonomous existence; they can live only inside cells. They divide when a cell divides and then are apportioned to the two daughter cells. When an egg cell forms in the mother, all its mitochondria are from her cells. Upon fertilization, the sperm cell injects its DNA into the egg—but not any mitochondria. Therefore, every mitochondrion that you are born with is maternal in origin. The mutation in the mtND4 gene that Jared inherited had to come from his mother. It is likely that it occurred by chance, during the creation of the egg, because his mother did not have the disease.