Sunday, September 29, 2013

DNA Test Types

We've seen how DNA inheritance works -- now what about the test types. What are they and why use one?

Here's a reminder of a man with his father's Y-DNA in blue Mizuhiki, his mother's mtDNA in purple Mizuhiki and his randomly inherited autosomal DNA in paper.

There are three main tests: autosomal, Y-DNA and mtDNA. I think the FGS2013 speaker sponsored by Ancestry explained the difference best. He told us that an autosomal test is designed to answer the question, "to whom am I related." The Y-DNA and mtDNA test are to answer the question, "am I related to you."

I've been reading a fascinating book of an adoptee's search for his father and how DNA was instrumental in his results. It's a wonderful story that tells how using two types of tests were needed to get the right answer to the mystery. He had to use both autosomal and Y-DNA tests. His book is Finding Family by Richard Hill.

The AncestryDNA test and the Family Tree DNA (FTDNA) Family Finder are both autosomal tests. A bunch of people take tests and the computers compare my DNA to that of everyone else. The best matches come to the top and it's up to me and my matches to figure out how we're related. The autosomal matching is most useful up to about 6 generations. After that, it quickly loses its usefulness. Autosomal tests seem to have settled at $99 right now.

Y-DNA and mtDNA are passed down fairly intact for many generations, though there are occasional  mutations. Both of these tests can be done at different levels of thoroughness and different prices. The more expensive the option, the more useful they are. However, they are very narrow in terms of what they tell us.

The Y-DNA test is used to compare DNA of men who share a surname to determine relationships and ancestry. Men who are adopted or in doubt of their parentage can use this test to look for the answers. One of the FGS2013 speakers who manages a surname project recommends the 67-marker level, currently priced at $268 at FTDNA.

The mtDNA test is fuzzier in my mind. I've recently upgraded my own from the basic test I took in 2005 to the "full sequence." When I see how it helps, I'll report back. The full sequence at FTDNA is currently $199.

I recently ordered for my father a kit from FTDNA. I paid for both an autosomal test and an mtDNA test. But I didn't order a Y-DNA test. Let me explain why I made the choices.

1. Autosomal. Because autosomal matching is only effective for a few generations, I can add one more generation of effectiveness for a fairly low price point. I will also be able to tell which of my own matches come from which side of my tree.

2. Y-DNA. My father's male line -- father-to-father -- is well documented back into Sweden. By the time we get back a few generations, the surname starts changing due to the use of patronymics. Our current surname is somewhat common in Sweden, but we are not related to many people who have the same name. Because Y-DNA is passed intact down the male line, it will be possible in the future to test my brother or nephews if we ever feel the need. So I chose to avoid this pricey test.

3. mtDNA. This choice is complicated to explain. I don't have a particular reason to test my father's mtDNA. We are fairly sure of his female ancestry, due to my own autosomal matches. However, recall that mtDNA is passed only mother to child and never father to child. My dad carries his mother's mtDNA. There are only four other living people with that same (known) mtDNA: two living uncles, a male cousin and one female cousin, who has no children. At the death of those five people, my paternal grandmother's mtDNA will be lost forever. So I paid for the test just to be sure I've captured it.

Another FGS2013 speaker asked the rhetorical question, why we do DNA testing. The answer that popped into my head (as well as hers) is "because we can."

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