Mitochondrial DNA (mtDNA) hardly changes, if at all, from generation to generation. This type of DNA is passed exclusively from mother to her children. Fathers cannot pass on their mitochondrial DNA
Brett Iley, a biologist at the University of South Carolina, offers this explanation:
Mitochondrial DNA (mtDNA) hardly changes, if at all, from generation to generation. This type of DNA is passed exclusively from mother to her children. Fathers cannot pass on their mitochondrial DNA.
Mutations (changes) do sometimes occur in mtDNA, but not often - less than once per 100 offspring. Therefore, it is likely that a particular person's mtDNA is identical to that of their mothers for 12 generations back. This shared genetic load allows different people to be linked over long periods of time. For example, if a certain type of mtDNA is mostly common in Africa, we can conclude that people from other parts of the world, who have the same type of mtDNA, are descended from African mothers.
Unlike most DNA molecules, mitochondrial DNA is not found in our chromosomes or even in the cell nucleus (the enclosed area in the center of the cell that contains all the chromosomes). Mitochondria are small structures, wrapped in a membrane, found in all cells in plants and animals, responsible for producing most of the energy needed for cell activity. Each mitochondrion contains its own DNA and its own mechanisms for protein synthesis.
Before humans began to travel around the world, the rare changes that occurred in mtDNA created unique types of mtDNA on each continent. Scientists can therefore associate a person's modern mitochondrial DNA with their continent of origin based on a section of mtDNA, known as HvrI, where mutations are most likely. Scientists can analyze the HvrI to find a record of all the mutations that occurred in the past as the mtDNA was passed from mother to daughter and generation to generation. These cumulative mutations are the basis of the unique mitochondrial DNA of each continent.
Within the continents themselves, there are differences in mtDNA between regions as well. Since a woman's offspring usually settle near her, the mutations originating in her mtDNA will be restricted to her area of residence. Of course, whenever people migrate from place to place they carry their mtDNA with them. For example, over the years there has been extensive migration of people in sub-Saharan Africa. A recent study showed that about half of all African mtDNA is therefore shared by people from different countries on the continent.
