Mitochondrial DNA: Meaning (information, definition, explanation, facts)

Mitochondrial DNA is DNA which is located not in the nucleus of the cell but in the mitochondria. It consists of 5-10 rings of DNA. It appears to carry 37 genes which are concerned with the production of proteins involved in respiration. However they all need sub units created by nuclear DNA in order to work. It has been widely believed that mitochondrial DNA is always passed on to offspring solely by the mother, although it has been reported that it can also occasionally be inherited from the father, e.g. in bananas. (Schwartz and Vissing, 2002).

Origin of Mitochondrial DNA

The existence of mitochondrial DNA also supports the endosymbiotic hypothesis, which suggests that eukaryotic cells first appeared when a prokaryotic cell was absorbed into another cell without being digested. These two cells then are thought to have entered into a symbiotic relationship, forming the first organelle. The existence of mitochondrial DNA suggests that, at one point, mitochondria were separate entities from their current host cells.

Mutations of mitochondrial DNA can lead to a number of illnesses including exercise intolerance and Kearn-Sayre syndrome (KSS).

See also Mitochondrial disease

It appears that the mitochondria in mammalian sperm are usually destroyed by the egg cell after fertilization. In 1999 it was reported that paternal sperm mitochondria (containing mt DNA) are marked with ubiquitin to select them for later destruction inside the embryo (Sutovsky et. al. 1999). Occasionally this process goes wrong, for example in inter-species hybrids.

Mitochondrial DNA has been studied to trace lineage far back in time. Svante Pääbo has published studies tracing the matrilineal descent of domestic dogs to 4 individuals. The concept of the mitochondrial Eve is based on the same type of analysis.

See also: single origin theory.

1. Marianne Schwartz and John Vissing, "Paternal Inheritance of Mitochondrial DNA", New England Journal of Medicine, Aug 22, 2002; 347:576-580. [1]
2. "Mitochondria can be inherited from both parents", New Scientist article on Schwartz and Vissing's report; [2]
3. Sutovsky, P., et. al. 1999. "Ubiquitin tag for sperm mitochondria." Nature 402(Nov. 25):371-372. Abstract available at [3] and discussed in [4].