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That and $2.29 = coffee

It’s another one of those things that comes up all the time in genetic genealogy.

Someone, somewhere, will tell you that you don’t really need to do YDNA testing — the kind of DNA test that looks only at the male gender-linked chromosome and defines the genetic characteristics of our father’s father’s father’s line1 — or mitochondrial DNA (mtDNA) testing — the kind of test that looks at the type of DNA we all inherit from our mothers and that defines the genetic characteristics of our mother’s mother’s mother’s line.2

HapJAnd, that person will often insist, you can get “the same” information from doing an autosomal test with 23andMe — that’s the kind of DNA test that works across gender lines and helps identify cousins who share bits and pieces of DNA you both inherited from common ancestors3 — since, after all, you will get your haplogroup if you do.

A haplogroup, in case you were wondering, is “a genetic population group of people who share a common ancestor on the patrilineal or matrilineal line. Haplogroups are assigned letters of the alphabet, and refinements consist of additional number and letter combinations.”4 In plain English, it’s the general branch, sometimes even the twig, on the human family tree where you and your ancestors — male or female — can be found roosting.

So, if you know your haplogroup from testing with 23andMe, you don’t really need to shell out for the specialized YDNA or mtDNA tests, right?

Um… wrong.

For two reasons.

First and foremost, the haplogroup is just the general location on the overall human family tree where your ancestral line can be found. By itself, it’s not enough information to help you compare your results to another person’s results in anything more than the most general way that will be even remotely meaningful in genealogy.

I don’t want to understate the haplogroup. It’s absolutely true that if you are, say, mtDNA haplogroup U5, then you do not descend from the same common female ancestor as someone else whose mtDNA haplogroup is K. You may surely be cousins, but not along your direct female line: you’d need to look somewhere else in your ancestry for the common ancestor you both share.

The same is true for the YDNA haplogroup. My Robertson ancestors were haplogroup J. That means we don’t share a direct male ancestral line with all those other Robertsons who’ve tested and turn out to be haplogroup I or R.

But when you turn it around — say, we found another Robertson who was J — that by itself just isn’t enough information to say he’s kin to our Robertsons. Right now, in the Clan Donnachaidh DNA project, there are three separate — and totally unrelated — groups of Robertsons, each of which is haplogroup J, but whose DNA is so different from the other groups that there’s no realistic chance we descend from the same man.

To be able to quickly and easily compare one set of haplogroup J Robertsons to another set of haplogroup J Robertsons, we need some information about DNA markers called short tandem repeats, or STRs, that are patterns in the DNA.5 And to get the STR markers, you need to do dedicated YDNA testing.

Don’t misunderstand, please: it’s a really good thing that 23andMe gives people their haplogroup predictions when they do autosomal testing with 23andMe. I sure don’t want 23andMe to stop providing those haplogroup estimates. It’s just not the same thing, and not as genealogically useful for direct line male research, as having the STR data you get from YDNA tests.

The same problem exists with the mtDNA haplogroup predictions from 23andMe: they’re nice to have, but not as complete and not as useful as you can get from dedicated mtDNA testing. My mtDNA haplogroup prediction from 23andMe, for example, is H3: a fairly large branch on the female haplogroup family tree. Dedicated mtDNA testing can break it down further, to a smaller sub-branch of H3g.

And since mtDNA haplogroups change so very slowly over so many hundreds, even thousands, of years, even that smaller sub-branch is too broad to be really helpful. In reality, especially for women like me in haplogroup H, only the very highest level of mtDNA testing is really useful for comparing my mtDNA to that of another individual.

Telling me I’m H3 tells me I’m very much like a huge percentage of women of European descent. Telling me I’m H3g is better, but still not enough. But telling me exactly what my results are, for me individually, with a careful look at every location within my mtDNA, is the kind of detail I can actually use in genealogy.

So what good is it to have a haplogroup, by itself, without more?

Except in the most general way, not very much.

It’s good enough to buy you a cup of coffee… at least if you’ll chip in $2.29 in cash.


SOURCES

Image: Haplogroup J (Y-DNA) by Rafy, Wikimedia Commons, CC BY 3.0

  1. See ISOGG Wiki (http://www.isogg.org/wiki), “Y chromosome DNA tests,” rev. 5 March 2014.
  2. See ISOGG Wiki (http://www.isogg.org/wiki), “Mitochondrial DNA tests,” rev. 9 July 2014.
  3. See ISOGG Wiki (http://www.isogg.org/wiki), “Autosomal DNA,” rev. 26 July 2014. See also Judy G. Russell, “Autosomal DNA testing,” National Genealogical Society Magazine, October-December 2011, 38-43.
  4. See ISOGG Wiki (http://www.isogg.org/wiki), “Haplogroup,” rev. 26 July 2014.
  5. See ISOGG Wiki (http://www.isogg.org/wiki), “Short tandem repeat,” rev. 20 July 2013.
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