What is mitochondrial inheritance?
The normal 46 chromosomes are inside the center of our cells, called the nucleus. Mitochondria are structures of the cell located outside of the nucleus in the cytoplasm, containing genes separate from the ones inside the nucleus.
Unlike nuclear genes, which are inherited from both parents, mitochondrial genes are inherited only from the mother. If there is a mutation of a mitochondrial gene, it is passed from a mother to all of her children.
Sons of an affected mother will not pass it on, but daughters will pass it on to all of their children, and so on. The first human disease that was associated with a mutation in mitochondrial DNA is called Leber's hereditary optic neuropathy.
Leber's hereditary optic neuropathy causes a painless loss of central vision between 12 and 30 years of age. Both eyes are affected at the same time. Males will not pass the gene to any of their children, but females with the mutation will pass it to all of their children, regardless of whether they are sons or daughters.