Wednesday, July 15, 2009

A Very Basic Introduction to DNA Testing

Why has genetic genealogy become the hottest tool in the genealogist’s toolbag?

DNA testing does not substitute for traditional genealogy; it supplements it. The object of testing is to find matches that will help you further your own genealogy.

Y-DNA testing, which is available only to men (because only they have a Y-chromosome), allows you to trace a man’s paternal line -- father to his father to his father, etc. Usually that line comes down to you via the same surname, or a spelling variation thereof. If you find a solid match to a man who has the same surname, then there is a 99% chance that you share a common ancestor with that man, and you want to get in touch to share pedigrees and try to determine who that ancestor was. Hopefully, the other person has taken his genealogy back further than you have so that you can piggyback on his work.

If there is no match within the surname group, there can be several reasons:

1. No one with matching DNA has tested yet.
2. Your line has literally died out, meaning there are no male survivors.
3. One or more of you having the same surname has a lineage break, sometimes called a nonpaternal event. This can arise because of adoption, choice, marital infidelity, or a host of other reasons, including faulty genealogical research. The nonpaternal event could have occurred many generations ago or very recently.

Once you have found matches to your surname – say, three men match at 35 of 37 markers, you can begin to sort them into sublineages. For example, the three men in our example may each descend from a different brother who arrived in America many generations ago. This is where mutations come into play. When a mutation (a small change to the actual DNA) occurs in one person, it is carried by all that person’s descendants and so serves as a defining marker. It shows up as a different value in one person’s haplotype. You will want to test several distantly related cousins to establish each one’s lineage.

mtDNA testing is available to both men and women and traces the maternal line – mother to her mother to her mother, etc. The genealogical value of mtDNA testing is not as strong as Y-DNA because mtDNA mutates very slowly. Advanced mtDNA testing can be very useful, however.

For more information, please visit http://The Genetic Genealogist and download the extremely useful ebook, "I Have The Results of My Genetic Genealogy Test, Now What?"

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