Does DNA Testing Really Help in Genealogical Research?
People use DNA tests to find their ethnicity, learn their roots or locate relatives. Results are private, so you only receive the amount of information your matches wish to share. Shared results may help correct mistakes in your family tree or find long lost cousins, but results may also destroy family stories or create unanswered questions. Results will only show probable ancestors and cannot replace careful research to prove your line.
What to know about DNA Tests and Results
Paternal and Maternal DNA Tests
There are 3 different kinds of DNA tests used to help with genealogy. The most common testing is autosomal, but there are two other types of tests that are done only by the Family Tree DNA company. Those tests are the direct Male (y-DNA) test and the direct Female (mtDNA) tests. Those test are relatively expensive and limited in the type of information returned. They are most reliable in learning the longest continuous and most distant relationships - but only for one line. For example, males who carry a continuous male line of a certain surname can determine with the y-DNA test if they match or do not other males tested from that same surname. However, if you buy the 37 marker test and achieve a perfect match with another, you only have a guaranteed common ancestor within 480 to 720 years ago. If two persons are tested on more markers and match, the probability is that their common ancestor was more recent. The test can establish that you do not belong in a certain line. The mtDNA test is like the y-DNA test but traces the longest continuous female maternal line, but only one continuous female line. The male y-DNA test is used more often than the female.
The Autosomal DNA Tests
The third type of test, and the most commonly used, is the Autosomal DNA test. Several testing companies such as Ancestry, 23 and Me, My Heritage and Family Tree DNA offer the autosomal test and the results should be the same regardless of the testing company. The autosomal test will estimate the percent of your ethnicity that comes from different regions of the world. This test will also match you to others who have some degree of relationship on either your paternal or maternal side. In matching relationships to other people tested, the results are most reliable for about four generations. Because autosomal DNA tests use DNA received from both our parents, with each generation the results become more and more diluted. When one gets back more than 4 to 5 generations, expected relatives often do not match since we get differing amounts of DNA from each parent. You may or may not get the answers you expected.
Generational Sharing of Autosomal DNA
Although a child will always share roughly 50% of chromosomes from each parent, there are no guarantees beyond that. Although highly improbable, two full siblings might NOT share ANY matching DNA segments in their chromosomes. Chromosome strands in a grandchild, for example, can be a random mix of the strands from the four grandparents.
What to do with DNA Test Results
It's best to add your own family tree to the website of the company doing your testing, before the test, and also to make yourself the "home person". That way, you will be able to see how you match others on their family tree when your results come in and also as new results are posted from new matches. The testing companies will have already calculated your estimated relationship to others tested who match you in some way and provide that information in your results.
Ancestry has the largest database of tested people. Millions of people been tested through Ancestry, so there is an increased probability of finding a cousin match there.
Once you are tested by any company and receive your "raw results" as well as your matches, you can upload your raw results to other sites to compare the results with people who used different testing companies. GEDmatch is one organization that allows people to upload their "raw results" for comparison to others.
More Information about DNA Results
Remember DNA results are private. You will have an ability to look at the trees of your matches, if they have added them to the site and made them public. You will also get a means of contacting your matches via the site or Email. They may or may not respond. Some people are searching for biological parents or other ancestors, and wish to retain privacy.
Unless you share a match, you cannot tell from a published tree if the owner has had a DNA test or not. You will only get a list of those with whom you share some DNA (in that company's data base) and an estimated relationship such as 1st, 2nd, 3rd cousin, etc. - but you will not learn which side of the family or how you are related. That information has to come from their trees or if they are willing to share more information with you.
You will get some other data that suggests how much DNA you share, increasing the likelihood of how recently you share a common ancestor. For example, Ancestry also reports how many centimorgans (cM) you should share with your matches. They estimate your relationship based on those results as well as reporting how many shared segments you have. For example, they show my first cousin as being my 1st–2nd Cousin; Shared DNA 975 cM across 35 segments. Our fathers were brothers, so we share grandparents as a common ancestor. Each generation away from a shared ancestors decreases the numbers reported. For example another cousin and I share a great great grandfather and our match shows 4th–6th Cousin; Shared DNA 48 cM across 4 segments. So we are now 4 generations back and the DNA results reflect that.
Conclusions
DNA matches may help you find trees with information that is helpful. DNA matches may help you connect with others who can help complete your trees. Do not expect everyone to reply to your requests. Do not confuse the the three types of DNA testing. Do not believe in DNA miracles.
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