Human Evolution

Why is mitochondrial DNA traced only through women?
Answered by Discovery Channel
  • Discovery Channel

    Discovery Channel

  1. Mitochondrial DNA (mtDNA) comes almost exclusively from women because egg cells have a lot of mtDNA while men's sperm cells have only a little bit. Mitochondria generate power for the cells, and because sperm cells use just a few mitochondria in their tails to swim to the egg to fertilize it, the mtDNA of the sperm usually disappear once fertilization occurs. On the other hand, the mtDNA of the egg pass on to all of a woman's children (male and female) but only women pass on their mtDNA from generation to generation. Because mtDNA is matrilineal and is not a combination of genetic material from two parents, tracking someone's lineage is easier.

    People who are closely related through their mother's side should have identical mtDNA because mtDNA passes down from mother to daughter practically intact. People whose ancestors were related centuries ago should have mtDNA that is almost identical. Mutations may have cropped up over time; otherwise the mtDNA would be an exact match. The fewer differences there are, the more recently the two people should be related.

    There are some disorders that may be associated with mtDNA. For example, limited evidence suggests there may be a link between mutations in mtDNA and and several forms of cancer, including the kidneys, liver, breast, stomach and colon. The mutated mtDNA may also play a role in leukemia and lymphoma. Leigh syndrome, a progressive brain condition with onset in early childhood or infancy, also might be linked to mutations in mtDNA. (Children who have it can develop slowly, experience muscle weakness and have difficulty moving or breathing.) Meanwhile, mutations in two mitochondrial genes are associated with a type of hearing loss known as non-syndromic, which is a type of hearing deficiency with no related symptoms or signs seen in other areas of the body [source: National Institutes of Health].

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