The Science of Sustainability

Genetic Tests: When No Means Maybe (Part 1)

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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

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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Category: Biology, Health

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Dr. Barry Starr

About the Author ()

Dr. Barry Starr is a Geneticist-in-Residence at The Tech Museum of Innovation in San Jose, CA and runs their Stanford at The Tech program. The program is part of an ongoing collaboration between the Stanford Department of Genetics and The Tech Museum of Innovation. Together these two partners created the Genetics: Technology with a Twist exhibition. Read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.
  • http://wellescent.com/blog/siteblog.php?entry=so-doc-whats-my-genome-tell-ya Wellescent Health Forums

    The detailed technical description of your assessment that you mentioned is part of the reason that I am not quite sure the concept of consumer genetics is ready for the public. With the ambiguities of the gathered information and the required background for interpretation, there is still value to having the expert acting as intermediary to the raw information.

    The websites will need a lot more educational material before they truly bring meaning to their users.

  • http://www.thetech.org/genetics/index.php Barry Starr

    23andMe has done a pretty good job of including a lot of educational material on their site but I am not sure yet if it is useful for the general public. That is why I wanted to try it out for myself. I'll keep you updated in future posts.

    I bet having someone there to help explain the data would be more helpful than a lot of web based stuff but the tricky part would be keeping the test affordable. Web content is much cheaper than a real live person. Perhaps they could offer an add on service that lets people ask questions that are answered by real, live people. My guess is that would be an expensive service!

    I might also check out their main competitor, decodeMe, to see how they are doing but they are pretty expensive and as a genetics educator, I am definitely not a rich man!

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  • B. Hunt

    I really enjoyed your article, and the diagram made your point well — until I realized that your paternal grandmother and maternal grandfather appeared to be siblings . I hope you will have a chance to update the figure since it emphasizes what a small portion of our ancestors are represented by mtDNA or Y chromosome data.
    Thank you again for a helpful reminder of how to interpret such results,