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Test them all!

The one thing that is abundantly clear is that understanding DNA testing and the way it can be used in genealogy is tough stuff.

siblingsWe have to understand what kinds of DNA tests there are.

We have to understand what those tests can and can’t show.

And we have to understand who to test to get the most from what the tests offer.

Compared to that, understanding those tick marks on an early census record seems easy!

And it’s that complexity that’s tripping up reader Gail as she tries to figure out who to test right now — herself or her brother.

“I am still wondering,” she wrote, “if I want the most complete results -– would it be better to test my brother versus myself as a female? Although I am reading it makes no difference it did make a difference with National Geographic since we got the female line only with myself and had to test my brother which resulted in duplication of the female with the addition of the male. Also, since the male or female DNA results showed only the direct line, will that change for the DNA tests from the other sources?”

Clearly some confusion going on here, so let’s go back to the basics and review the three basic types of DNA tests.

First, we have YDNA — the kind of DNA found in the male gender-determinative Y chromosome that only men have.1 It gets passed from a man only to his sons and from his sons only to his grandsons and from his grandsons only to his great grandsons, with few changes down the generations.2

That’s the test Gail’s brother has already taken with National Geographic, and that gave him what she refers to as “male DNA” results. That tells her and her brother only about their direct paternal line: their father’s father’s father and so on (plus all of the sons and grandsons of those men) share the same YDNA.

What does that type of test tell us? It can help us answer a key question: am I descended from — or at least related to — that one man? So it’s an excellent test for genealogists, but for this test they have to have a male candidate to test.

Second, we have mitochondrial DNA, or mtDNA — the kind of DNA we all have that serves as the energy producer for the cells in our bodies.3 It gets passed from a mother to all of her children — male and female — but only her daughters can pass it on to her grandchildren.4

That’s the test that Gail and her brother have both taken with National Geographic that she’s referring to as the female line because it tells them about their direct maternal line: their mother’s mother’s mother and so on (plus all of the children of all of the women in a direct line of descent) share the same mtDNA.

What does that type of test tell us? It can help us answer a key question: am I descended from — or at least related to — that one woman? It’s a tougher test to figure out because of the inheritance pattern: you can test a son if you’re looking for information about his mother’s mother’s mother’s line, but you can’t test that son’s children since they have the mtDNA of their mother, not their father. So it’s an excellent test for genealogists, but only if they have the right candidates — male or female — to test.

Third, we have autosomal DNA — the kind of DNA we all inherit from both of our parents5 in a mix that changes, in a random pattern, from generation to generation in a process called recombination.6

That’s the test that Gail is really asking about right now, and wondering whether she or her brother would be better to test — and whether it makes any difference who gets tested.

What does that type of test tell us? It tells us about all of our ancestors back within four or five generations, to help us answer the question: am I descended from — or at least related to — that couple? So it’s really most useful for finding cousins who share some portion of DNA with us with whom we can then share research efforts.7

And because that recombination bit happens every single time a child is conceived both Gail and her brother should be tested. Recombination is purely random, so Gail could well have inherited some fairly substantial chunks of DNA that her brother did not inherit — and vice versa.

And to be sure of getting the most from autosomal testing, not only should Gail and her brother both test, but they also want to test everyone else in the family — parents or grandparents still living, other siblings, aunts, uncles, cousins — that they can convince to test.

Each family member will have cousin matches in the DNA testing databases that the others won’t have — and some of those individual matches may provide the keys to some enduring family history mysteries.

Bottom line: when it comes to autosomal testing, test everybody you can afford to test!


  1. ISOGG Wiki (, “Y chromosome,” rev. 18 Jan 2015.
  2. Ibid., “Y chromosome DNA tests,” rev. 27 Nov 2014.
  3. What is mitochondrial DNA?,” Genetics Home Reference Handbook, National Library of Medicine, US Department of Health ( : accessed 18 July 2015).
  4. ISOGG Wiki (, “Mitochondrial DNA tests,” rev. 15 May 2015.
  5. ISOGG Wiki (, “Autosomal DNA,” rev. 30 June 2015.
  6. ISOGG Wiki (, “Recombination,” rev. 14 June 2015.
  7. See Judy G. Russell, “Autosomal DNA testing,” National Genealogical Society Magazine, October-December 2011, 38-43.
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