Just to note i said there that mitochondial DNA did not change much from generation to generation this is not true( I was getting mixed up as usual) it actually has quite a high mutation rate but has still been used successfully to study the female line.
It is more often used in ancient DNA studies due to there being lots of them in the cell and also the small size of its chromosme is less likely to fragment in the way the cells much larger nuclear DNA does over time.
please excuse my error
love
carolinex