The vast majority of our DNA is found in the nucleus of the cells that make up our body - this is the DNA that is tested in a usual paternity or relationship test. However, in addition to the nuclear DNA, a small amount of DNA is also found in other parts of the cell - organelles called mitochondria.

Sometimes described as "cellular power plants", mitochondria are involved in converting food molecules to energy and are present in most cells in large numbers.

The DNA in mitochondria is particularly interesting as it only inherited from the mother and can therefore be used to trace the "maternal line" back through multiple generations. Mitochondrial sequencing is a lengthy and complicated type of DNA analysis which is occasionally used for forensic and relationship testing.

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