Another DNA oddity - genesis/23andMe/LivingDNA

Question

On genesis in the one-to-many list my Dad (CB5898100 23andMe) has a match with Roberta Estes (EG1550074 Living DNA) with total 26.4cM, longest 11.1 cM, for an expected 4.5 generations. However a one-to-one compare gives one segment at 7.4cM, for an expected 7.5 generations. There is another 6.4cM segment, but even with that the discrepancy between one-to-many and one-to-one seems rather large.

But when I check on gedmatch using Dad's Ancestry test A136143, there is no match with any of Roberta's kits - T524738, M149963, A736716.

So, is there something about the combination of genesis/23andMe/LivingDNA that says either this is a good result or a spurious one?

Comments

Do you have her permission to publish her name and kit numbers on an open forum such as G2G? If not, please anonymise the details in your post to protect privacy.

Answer 1

Every company tests a different set of SNP's, and there can be a fairly large divergence between the tests.  Plus, you don't get a successful read for every SNP in a test, meaning your result may often only contain some 680000 SNP's of the 700000 they may advertise.  So when you compare tests, especially from different companies and chipsets, they can only compare the SNP's common to both.  That's usually well over 600000 for tests from the same chipset and company, but often 400000 or less for other comparisons.  I do agree your results demonstrate a surprisingly large variability, a little larger than I would have expected.  I tried my own kits against hers and found similar variability, although not as large as yours.

On the question of permissions and privacy, Lynda, it seems to me that when one publishes their name and kit ID's, there is an implicit permission to use them.  If the person appeared to be new, with only one kit, then I might be concerned they may not be fully aware of the exposure.  But when someone has 3 or more kits, publicly listed, that would seem to qualify as someone who knows what they're doing, at least to me.  (At the same time, it's always nice to see people looking out for each other, concerned for others welfare and safety!)

Comments

In addition, something Edison has written about recently, the tested SNP's are a very tiny minority of the total SNP's possible, and are scattered somewhat randomly  across the chromosomes.  One company may be testing quite a few SNP's in a particular segment area, and the other may not, so there may not be a minimum number of SNP's common to both tests to qualify as a candidate for matching, within that segment area.  There are different algorithms, but they all need a minimum number, sometime as little as 200, but more often as many as 500 SNP's within a segment, no matter how long the segment is.