Tuesday, January 27, 2015

Disappointment with Ancestry Admixture or Composition Results

Since many members of my groups on facebook research possible Native American ancestry, it is not unusual for me to see posts about how disappointed they are that there is not any, or very minuscule, amounts of Native American showing up on their admixture or composition results.

To be honest, there are times I honestly think that they got the results they were supposed to, however, there is a very good reason that someone does not have the results they think they should. It is called recombination and it is how our genes are passed down.

To illustrate this fact, I am going to use examples from my mom, her cousin SH and her nephew JM with genealogically proven third cousins once removed. Genetically speaking a third cousin has the estimated DNA of 0.781 percent or 53 cM,  a third cousin once removed has  the estimated amount of DNA around 0.391 percent or 26.56 cM shared, and a fourth cousin (for JM) should share about 0.195 percent or 13.28 cM of DNA.

Mom has matches with two sisters and one daughter on her Hager side. The sisters are 3rd cousins  to my mother and SH and the daughter is a 3rd cousin once removed. (for JM that means third cousin once removed and fourth cousin).There is another Hager descendant also of the same degree they match as well.

Mom matches one sister at 145 cM, the other at 130 cM, both third cousins, the daughter at 65 cM and the last at 9.9 cM both third cousins once removed.
SH matches one sister at 40 cM, the other at 74 cM, the daughter at 39 cM and the last at 5.2 cM
JM matches the one sister at 29 cM, the other at 0 cM, both third cousins once removed, andthe daughter at 22 cM and the last at 7.7 cM, both fourth cousins.

Another example is a genealogically documented third cousin once removed on the Collins family.
Mom matches him at 38 cM, SH at 134 cM and JM not at all.

So let's say, hypothetically speaking, that the native DNA was represented by one of these ancestral common ancestors DNA. As you can tell by the numbers, the amount passed on varies significantly, even though the genealogical distance is the same for SH and my Mom. In the case of JM, when he has no shared DNA it means he didn't receive any of that genetic material. If this portion of the DNA represented the person who was passing on the Native DNA it would mean yep, he's not going to show a percentage even close to that of his biological Aunt.

It's obvious that there is some kind of sticky DNA going on in some of my mom's family, she is sharing 1.7-1.9 percent of DNA with her Hager cousins, but only 0.5 percent with her Collins one, and on the flip side, her first cousin is sharing .0.5-0.9 percent with his Hager cousins and 1.8 percent with his Collins cousin.In both cases, the lower percentage is more the average, so the larger matches while possible, are not typical.

Ancestry composition is passed the same way as this DNA, it is a recombination draw of the lottery in what gets passed on to each generation. So how is it my Mom actually shows a percentage of Native DNA close to her actual degree of blood based on genealogy and the Dawes? Luck for the most part, when you stop and think that her last full blood ancestors on the Trahern only side were born in the 1770's, with mixed bloods intermarrying until her great great grandfather married a full blood. Even at that, Mom's great grandmother could only be 11/16 Native American (her father was 3/8 and her mother full).

Based on the Dawes where she claimed only 1/2, mom's Choctaw DNA should be 1/16 or 6.25 percent, if you include the reported actual, it would be11/128 or 8.6 percent . Her 23 and me results show her at 8 percent, and gedmatch admixtures average 8-10 percent based on the program.

Even though her great grandfather and her grandfather are by family history Native American, their contribution would be so minuscule that it's not even worth computing.

So if your disappointed with your admixture results, you really need to look at some of your close family and test them. First cousins, and even siblings do not always share an equal amount of DNA from all their contributors.

1 comment:

  1. The filters used for admixtures also have a notoriously small amount of data used for comparison. I believe they only have 100 or so native samples vs thousands for the others. It skews the results. Unfortunatley using DNA at this point in time to trace native ancestry is a bit of a gamble.