Genealogy Today, by Betty Lou Malesky, CG
DNA Tests & Genealogy
DNA stands for DeoxyriboNucleic Acid. There are two types of DNA used in genealogical testing. Y-DNA comes from the Y chromosome and Mitochondrial DNA, or mtDNA, comes from the X chromosome. Men have both an X and a Y chromosome-Y-DNA and mtDNA. Women have two X chromosomes, however, so they only have mtDNA.
Y-DNA is used for tracing surname ancestry. MtDNA is used for tracing deep ancestry, ethnic background such as African, Asian, Middle East, European or Native American, but will not help find specific ancestry related to your surname.
Y-DNA is passed from father to son. Working backwards, a man's DNA is from his father, his father's father and so on. When tracing ancestors with the same surname it is sometimes difficult to determine if they have the same lineage. If a man's Y-DNA matches another man's Y-DNA and their surname is the same, it indicates they have a common ancestor and can also determine approximately how many generations back that common ancestor is.
The more markers that match another's test results, the closer the common ancestor will be. Family Tree DNA tests for 12, 37, or 67 markers. As the number of markers tested increases, the cost increases. If two men match on all 12 markers, there is 50% probability of a common ancestor back 7 generations and 95% probability back 29 generations. Fewer than 10 matches means the men are probably not related. A match on 37 markers indicates 50% probability of a common ancestor back only 2 generations, i.e., 50% probability of having the same grandfather, and 95% probability of a common ancestor back 7 generations. When 37 markers match for persons with the same surname, existing research documenting ancestry may help determine the exact relationship or help to pinpoint an area for additional research.
I am not an expert on DNA, but the detail above was contributed by Bob Vint, another Green Valley genealogist who has studied the subject. Bob had his DNA tested as did another man named Vint because they couldn't establish a relationship with their existing documentation. Both have Scottish ancestry and Vint is not a common surname, but they matched on only 9 of 12 markers. Extending the test to 37 markers verified the 12 marker result-either they are not related or there is an undocumented paternity event in their ancestry somewhere. Bob is hoping to find others with the Vint surname who will participate in the test project.
Family Tree DNA has processed over 500,000 DNA tests since its inception in 2000. At its Houston, Texas, headquarters it conducts research and development and currently offers over 200 types of advanced DNA tests for its customers. With the largest database in the world of DNA test results for matching purposes, the chance of finding long lost relatives is enhanced. Tests are also useful for any of over 3,000,000 adopted persons in the U.S., or their descendants hoping to find clues to their ancestry.
All of Family Tree DNA's tests are processed in the research labs at the University of Arizona Genomics Analysis and Technology Core. Using state-of-the-art methods, the center provides a wide range of molecular biology services to industry and government. To read more about how DNA was used to prove a relationship in the Eastman family see http://blog.eogn.com/eastmans _online_genealogy/2009/07/how-dna-proved-my-family-tree-connection.html.
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20 September 2009