Genetic Tests: When No Means Maybe (Part 1)

Genetic tests often don’t give as much information as you might think.In a previous blog I talked about getting my DNA tested with 23andMe.  Well, I got the email the other day saying that my results were ready.  So I logged on and up popped this screen pictured to the left.

All sorts of goodies to try out!  I feel like a kid at Christmas.

The first thing I thought I’d do is check out my ancestry.  My grandfather’s grandmother was supposedly Native American and so I wanted to find out if I could see that in my DNA.  (This relates to my supposed relationship with the outlaw Sam Starr but that is a different story.)

23andMe has this Native American testing app in their 23andMe Labs section.  I clicked on my data and up popped this result:

Recent Native American ancestry is unlikely

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Has it all been lies?  My great, great grandma wasn’t Native American?  Not so fast...

A “no” answer on a genetics test doesn’t necessarily tell you a lot.  (And sometimes, the “yes” answer isn’t so helpful either!)   Now as a geneticist, I know the drawbacks of ancestry tests like these.  What I wanted to see was if 23andMe did a good job of explaining them.

I first checked out my mitochondrial DNA (mtDNA) and my Y chromosome data.  These DNA don’t change a lot from generation to generation and so are really good at tracing ancestry many generations back.  Their downside for me is how they are passed down.

The Y chromosome passes from father to sons.  My great, great grandma didn’t have a Y to pass on so of course my Y chromosome data wouldn’t show that she was Native American.

mtDNA passes from mom to her children.  At first this sounds promising since we are talking about my great, great grandma until we realize that I am related to this woman through my grandfather.  His mtDNA died with him (except for his female relatives and their descendants) so that is lost to me as well.

Here is what 23andMe has written under interpretation of my mtDNA and Y chromosome results:

This mitochondrial DNA haplogroup is inconsistent with Native American ancestry along the maternal (mother's mother's mother's ...) line.


This Y chromosome haplogroup is inconsistent with Native American ancestry along the paternal (father's father's father's ...) line.

I suppose this says what I just said but I am not sure how many people would really appreciate the limitations of mtDNA and Y chromosome data from this explanation.  There wasn’t a link to a more explicit discussion of the limitations of this sort of testing and there wasn’t anything I could see from a quick glance at the ancestry part of the site either.  An explicit explanation would be good or maybe a figure like this one:

gene-tree

To me, this drives home the point that there is a whole lot of missing ancestry.  It might help if they had some sort of family tree app where you could indicate as much as you know about family relationships.  Once you’ve inputted the data, it would spit out what tests results would be useful to look at.

So the mtDNA and Y chromosome test results are of little use to me in this quest.  (And of little use to me in general as it confirms my pasty whiteness.)  Next blog I’ll deal with the rest of my DNA and what that can and can’t tell me about my great, great grandma.

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