Comments on: Ancestry at 23andMe: What Can You Learn?

By: Kate

Kate — Fri, 01 Oct 2010 00:15:23 +0000

I love your service and really appreciate all the information that has been outlined for us.Before testing I had only a minor understanding of my ancestry,now I’ve infered alot more than I even though would have been possible,information I could’nt find through traditional methods.Ancestry finder and Relative Finder has been the most illuminating tools but they are all helpful and useful.I had no idea when I signed up that I would end up with this amount of ongoing info on my ancestry.

By: Jim Owston

Jim Owston — Sat, 18 Sep 2010 00:56:47 +0000

Shirley:

Thanks so much. This is one of the things I like about the 23andMe family – you listen to your customer base. I’ve seen this time and time again. Keep up the great work.

Jim

By: Shwu

Shwu — Sat, 18 Sep 2010 00:55:50 +0000

Hi Harvey,

Interesting scenario, and one that is actually not uncommon. There are two things that could be happening here. One is that Ancestry Finder (which is where I’m guessing you’re seeing this information) isn’t updated in real time, so your results and your children’s results might be out of sync temporarily. Another explanation has to do with how segment boundaries are determined. When we are comparing segments between people, if one person has a “TT” at one SNP and the other person has a “CC”, we can definitively call that a mismatch and end the segment there. But if one person has a “TT” and the other has a “CT”, we don’t know if that’s an endpoint or not — the one ‘T’ that the second person has could continue the run. It could be several or many more SNPs later before a definitive mismatch occurs. So if you are the “CC” in the first scenario, you wouldn’t show up as sharing that segment with the other person, but if your children are “CT”, they might. Differences in segment sharing like your case are more likely to happen as the segments get shorter, so if the “Czech” segments your children have are all in the 5-8 cM range, that could be the explanation.

We might tackle this general situation in a future post, but if you’d like to discuss your question in more detail with one of our scientists, feel free to contact help@23andme.com with your question and as much clarifying information (screenshots, etc) as you can. Thanks!

By: Shwu

Shwu — Sat, 18 Sep 2010 00:47:06 +0000

@AB In general, our autosomal relatedness predictions are accurate only up to the 5th-10th cousin range, so the maximum time frame would be somewhere around 300 years (but probably less). If you know the predicted relationship (e.g. the match is listed in your Relative Finder) it might help narrow that time frame. If it’s below our Relative Finder threshold it would be very difficult to estimate. Ashkenazi ancestry does make things more challenging since there is more background sharing in this population. It might not necessarily increase or decrease the time frame, but it could certainly make determining the common ancestor more complicated.

If you’d like a more detailed explanation, please contact help@23andme.com and reference this post!

By: Shwu

Shwu — Sat, 18 Sep 2010 00:10:31 +0000

Brad, very good points. I’ve tweaked the post to reflect some of what you brought up. We certainly want to get across the fact that Y and mito aren’t everything, and in fact are only a tiny part of the overall picture.