Discovering your GeoMother™ using mitochondrial DNA

Mitochondria are tiny structures found within the cytoplasm of certain types of cell. They contain the enzymes that are necessary for energy production, which is why they are often referred to the “powerhouse” of the cell. They are only passed along by the mother because at fertilisation there is no cytoplasm in the sperm and so no mitochondria are received from the father.

Mitochondrial DNA, abbreviated as mtDNA, has its own genome, which is very small – only 16,569 base pairs in length and less than 1/300,000th of the total length of DNA molecules found in the nucleus of a human cell. Nevertheless, mtDNA provides scientists with a very powerful tool for researching ancestral female lineages. This is because unlike with other forms of DNA, the major part of mtDNA does not get changed when it is passed down from mother to child.

Occasionally, however, as mtDNA is passed on from one generation to the next, its genetic code does undergo a very small alteration. The vast majority of these alterations are completely harmless and so are eventually passed on to succeeding generations. Over time, further small alterations occur. In this way, separate family lineages become increasingly different from each other.

Building a global family tree
By comparing two individuals’ mtDNA, it is possible to judge how closely they are related. If their genetic codes are very similar, we can say that they share a common female ancestor in the recent past. The more differences that have accumulated in their genetic codes, the more generations have passed since their last common ancestor.

Scientists have used this basic principle to compare the mtDNA from thousands of men and women living all across the planet. They have used their findings to construct a global family tree of female ancestors.