The human cell contains a number of components known as organelles. Mitochondria are amongst these organelles and in these we find mitochondrial DNA. MtDNA is not the same as the DNA we usually talk about; normally when we talk about DNA we talk of nuclear DNA which is the DNA found in the cell nucleus. Mitochondrial DNA in humans is exclusively inherited from the mother and the DNA remains relatively unchanged as it is handed down from generation to generation.
Males too have mitochondrial DNA but this is destroyed in the very early stages between fertilisation and embryo development. In forensics, unidentified remains can be identified by comparison of their MtDNA with possible living female relatives. An MtDNA testing can be used to establish maternal lineage and show whether two individuals come from the same maternal line. Men possess MtDNA but do not pass it down to their children, only females pass it to their children. Thus an MtDNA test is very useful in ancestry testing and Relationship Testing. It can determine whether two or more people share the same maternal line, but will not establish how close or distant the relationship is.