Great information! thanks Michael. One comment I would like to insert here. A mother passes her maternal dna (mtDNA) to all her children, both her sons and daughters. A father passes his paternal dna (Y-DNA) only to his sons. Therefore, their sons have both mtDNA and Y-DNA, while their daughters have only mtDNA. Their sons cannot pass their mtDNA to their children, so their mother's mtDNA stops here for them. (If one of the sons marries, his children will have the mtDNA of THEIR mother.) Their daughters however continue to pass the mtDNA to their children. In this way, mtDNA very seldom mutates or changes, but Y-DNA changes after so many generations. So ... The male can test both his mtDNA (from his mother) to determine his mother's origins, and his Y-DNA (from his father) to determine paternal ancestry. Men get to do both! while a female can only find out about her mother's line. Not fair! It's true that Y-DNA is "diluted" after so many generations. But depending on the number of markers tested and compared, it is still a pretty good predictor of possible paternal ancestry. It can't "name" a person as a male's paternal ancestor, it only shows who, in his lineage, could have been a common ancestor to another person with the same results as his. In other words, if the markers of both James HAGARTY and Charles HAGARTY match, then they do share a common ancestor. The more markers that match between them determine the closeness of the common ancestor within so many generations; for example, do they share a grandfather, or a great-grandfather, or even a paternal ancestor ten generations away? If they are exactly the same, they are most likely brothers, sharing the same father. The female can only have her mtDNA tested. But since mtDNA rarely changes over time, it is a pretty good indicator of where her maternal gr-gr-gr-gr-(etc) grandmother came from --- a tribe or group in a certain geographic location. But if one person compares his/her mtDNA results with another, the tests cannot determine who an ancestor is, or the common ancestor shared, except in the most general sense of both descending from the same tribe. I have a female friend (African-American) who has learned that she and a male friend both descend from the same tribe in Niger, Africa. But through mtDNA, she has learned where her slave ancestress came from and so she now has a sense of her origins. DNA test results are actually a mathematical percentage of being related or sharing a common ancestor and don't mean anything unless you have someone else to compare your test results with. So the higher the number of markers tested and compared, the higher the percentage of actually sharing the same common ancestor, and the closer you come to saying you've found a cousin! It's all so interesting. I can't wait to have my mtDNA tested. Maybe ... I'll find the Asian in the Irish woodpile after all. Cheers! Phyllis >The blood type analysis and the DNA analysis are two >different things. The people doing the DNA analysis >are geneticists. They have found different genetic >patterns from identifyable genetic markers from which >they have classified populations throughout the world >into groups called haplogroups based on their genetic >similarity. This is based on the changes occurring in >the genetic structure over time, which is very, very >slow in the case of mtDNA. However, it only works by >tracing back on the male line using the Y-chromosome >DNA from father to grandfather to great-grandfather >etc., or conversely by using the mtDNA from mother to >grandmother to great-grandmother, etc.. Essentially, >we are talking about variations on the same theme >because if you go back far enough, you arrive at a >particular woman with a particular genetic makeup who >becomes the mother of everyone. This can be proven by >science because we know from archeology the time frame >in which homo sapiens first appear, and we know the >approximate rate of variation in mtDNA. Assuming the >hypothesis that there was one original mother, >scientists can calculate when she lived based on the >known approximate rate of variation and the observable >extent of genetic variation throughout the world. >Then, they can compare that with the known time frame >for homo sapiens living on planet earth. If we assume >more than one original mother with different genetic >makeup, we would have to have much more genetic >variation today than what scientists actually observe >in order for it to fit within the time frame. If we >assume more than one mother with the same genetic >makeup, i.e. identical twins, then we also have to >admit that both had the same biological mother which >gets us to the same result of one original mother. > > > > >Michael O'Hearn >