Tuesday, March 26, 2019

DNA From Which Parent?

Some of the DNA companies will tell you which side a match is from if one or both of your parents have tested with that same platform.  I'd tested with 23AndMe back in 2013, but both of my parents only just tested.  My mother's results came in today, but we're still waiting for my father's.

But since only my mother is in the system at this point, 23AndMe is looking at all of my matches and trying to predict through which parent we are connected.  Well, this might work really well if you're not from an endogamous population, but if you are, it isn't so helpful.
My closest matches on 23AndMe.  Check out the prediction between each relationship--all on the mother's side!

Look at the predictions for each match--all of them are "Mother's side."

Since both of my parents are Jewish, pretty much everyone who is also Jewish who has tested with 23AndMe matches both of them.  Take a look at this view--even though my two closest matches on 23AndMe are known close relatives on my father's side--a first and a second cousin--23AndMe tells me that they are related on my mother's side.

This can send people off in the completely wrong direction when trying to track down a match, particularly if they've only been able to test one parent.  (As an aside, this makes looking at shared matches similarly difficult, when dealing with endogamy.)

So this short post is for those with endogamous ancestry and a warning to be very careful of both shared matches as well as using these "which parent is connected to the match" sort of hints--not just on 23AndMe, but on all of the testing platforms.

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  1. We, the mischlingers, don't have this kind of problems! :-)

  2. Not surprising and good to know! (I am skeptical of most anything the testing companies say---from ethnicity breakdowns to relationship distances.)

    1. They don't account for endogamy well in any manner!

  3. So I have a question. How reliable would you say Gedmatch is in their estimates that your parents were not related. Mind you asking that I am aware I do not have blue eyes as they suggested I do though one of my daughters did get similar blue eyes to the ones the offered as my probable eye color.

    I ask because it says my parents are not, but it's become very apparent that my maternal grandmother was from same vicinity as my father's mother's family and if not related think there may have been some marrying between relatives of my Grandmothers.

    1. GedMatch saying they aren't related doesn't mean they were. They are looking for segments on your chromosomes where you got the same values from both parents.

      Let's say your parents were related and had a shared segment on chromosome 1 in common. You got 50% of each parents' genes, so perhaps you got that segment from your mom but for that segment from your dad, you got his other copy of that chromosome 1 segment. Then there's no way for GedMatch to know that both of your parents had shared that segment, so they'd find no relationship.

      Make sense?