In anthropology, mitochondrial DNA is useful for the purpose of tracing ancestry. It is very useful for telling which people are related to which other people. This is because it is passed down through the mother and does not recombine.
It is also useful for telling how long ago people were related. So anthropologists have used it to construct "family trees" of the human species.
If you follow the link provided and scroll a little way down to the bold heading "Mitochondrial DNA" you will find a good description of the various ways in which this kind of DNA is better suited to this task than other kinds of DNA.
Mitochondrial DNA is the genetic material from mitochondria, which is the cellular organic cell, responsible for generating the necessary energy. It is similar to bacterial DNA,but the is a bicatenary circular molecule, closed, without extremities.
It's important feature is that mitochondrial DNA does not recombine. The only changes that can occur in mitochondrial DNA are summarized exclusively as mutations transmitted over generations, but also within a single generation.
When a sperm fertilises an egg,it falls off it's tail and all cellular material, except the nucleus that contains all the hereditary information (nuclear DNA). This means that dropping off the rest of the cellular material, it drops off the mitochondria,also. The only mitochondrial DNA which is occurring is the one from the egg content.Hence, we conclude that hereditary mitochondrial genetic information is transmitted to generations, only by maternal path.
Thus, it was developed the theory of primordial existence of a mitochondrial DNA, called mitochondrial Eve.