What Is Mitochondrial DNA?

A sperm and an egg unite to make a fertilised ovum, which eventually can turn into an embryo.  The sperm and the egg each bring equal amounts of DNA to the embryo.. or do they?  Actually, a small amount of extra DNA is in the egg, this is called mitrochondrial DNA (mtDNA).  Mitochondria are tiny mini-organs in the fluid-filled space between the cell nucleus and the cells' outer membrane. mtDNA is only passed down the female line.  Everyone has mtDNA, but you only inherited it from your mother, and she from her mother, and so on.  As such, it is a good way to track female inheritance.  

mtDNA has a few specialised and unique roles in cells.  These are especially to do with energy production. Things like athletic stamina may come more strongly from the female rather than male parent.  Certain disorders, especially of the lungs and respiratory system, may be treated, eventually, by targetting drugs that act in response to mtDNA.