Mitochondrial DNA is found in the cell organelles (organelles are components of cells) known as mitochondria. When we talk of DNA we commonly refer to the DNA found in the cell nucleus, or the ‘control-centre’ of the cell. In relationship testing, MtDNA is important because it can be used to track maternal lineage; this is because MtDNA is only inherited from the mother and is inherited by her children unchanged. Male MtDNA exists but it is destroyed sometime around conception. MtDNA remains relatively unchanged as it is passed on from mother to both male and female offspring.

As stated, females pass on their MtDNA to their children but males do not. The fact that it remains unchanged means it is a reliable means of determining whether two individuals share the same maternal lineage but not how close or distant the relationship is.  MtDNA was used to identify the remains of the Russian imperial family through use of MtDNA provided by Prince Philip, who decedents from the same maternal line as Queen Victoria. Thus, to genealogists and other people wishing to have a relationship DNA test or an ancestry test, MtDNA testing can be a valuable tool.