After reading Bryan Sykes' book, "The Seven Daughters of Eve", I came across a chapter which disucssed Mitochondrial DNA and how it is used to link back ancestory of organisms. I do understand this concept where the mitochondrial DNA is inherited from the mother and therefore is constant unless it undergoes mutions over the generations, but what I would like to understand is how Mitochondrial DNA can be used to determine relationships between organisms..

Thanks for the help!