Tuesday, February 25, 2014

A Sticky DNA Puzzle

Have you read Roberta Estes' recent post on DNA generational inheritance? If not, I encourage you to do that. The numbers made my head spin and I didn't even try to follow the math and statistics. However, her points are extremely important for those of us working with DNA and genealogy.

What I took from it is that inheritance is not really 50-50 from each parent. And some DNA seems to stay together (clump) and pass nearly unchanged for many generations (sticky). And sometimes what looks like a match is merely randomness. That's known as IBS or identical by state.

Of course we already know that siblings share only about half of their DNA.What's surprising about her charts is the way we inherit all versus nothing of a parent's DNA segment, rather than having interspersed inheritance. So even if we expect a match with a certain individual, we might not see such a match. It doesn't prove there's no relationship.

My Sticky Clump

I'm glad that Roberta wrote this post, as I'm dealing with matches of my own that appear to be both clumpy and sticky. I wrote before about a group of people with a significant match on chromosome 16. Unlike her example, we don't yet know the source of that DNA.

My contact, "John", and I theorized that the connection might be in our Weakley County, Tennessee, families. Another theory is that the clump belongs to a Williams ancestor. Both of these lines belong to my mother.

Surprise Number 1

My Dad's DNA analysis threw a monkey wrench into the theory. Dad (not Mom) matches the group!

Notice how the sticky DNA (the blue area) did not pass from my daughter to my granddaughter. It entirely disappeared. That sudden disappearance makes me think this is a clump that passes nearly unchanged through many generations.

My Dad has a lot more holes in his tree than my Mom does, so finding the source of this DNA will likely fall to other members of the group. Sorry, team!

Surprise Number 2

I got another surprise from Dad's DNA. My father's ancestry is largely Swedish, which would include ancestry from Finland and Norway. My mother has no known Scandinavian ancestry.

Working at GedMatch, I picked all my matches with email addresses ending in "se" and "fi". These are people who currently live in Sweden and Finland. I cross-matched those four people with my four kits, using the 3D chromosome browser tool.

Notice Ms. T matches me at a higher threshold (yellow) than the other matches. She also matches me on the X chromosome for an additional 8 cM. Yet she does not match my Dad at all. Nor does she match my daughter or granddaughter.

Also notice how the match totals fall within our family kits (red). It isn't exactly 50 percent in each generation, but it's close.

Another interesting item is that Mr O doesn't match to my daughter or granddaughter. Yet we think we're related through a particular ancestor from Hannäs, Sweden. The matching DNA vanished, just as the chromosome 16 clump did.

Back to Ms. T. I had always assumed she was a match on my Dad's side. Now I have to consider three options:
  • my Mom has Scandinavian ancestry
  • Ms. T has ancestry from Germany or the British Isles
  • the match is IBS (random) and not a real match

If Ms. T is an actual match, consider that the only way to identify that match was by testing my DNA. This shows how important it is to test everyone that you can. I'll be looking for more family volunteers soon!

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