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Archiver > GENEALOGY-DNA > 2009-09 > 1253977132


From: "Roberta Estes" <>
Subject: [DNA] 23andMe Autosomal Testing - Will 3 Sisters Test the Same???
Date: Sat, 26 Sep 2009 10:58:52 -0400


I've been writing tidbits for my project and people have been asking to
repost them to their projects. I'm posting them here, not because you folks
necessarily need them, but so that if you are interested you can repost to
your groups to encourage participation and help with the understanding of
DNA. If nothing else, this has greately encouraged interest and I've
actually gotten several joins at FTDNA as well from the increased interest
in DNA testing.

Here's the text of this one and the others will follow shortly.

Today's question was whether three sisters would test the same. That's a
great question.
First, take a little internet journey and watch a short clip about how
autosomal inheritance works. You can find it at
http://www.smgf.org/education/animations/autosomal.jspx and it shows you
clearly how you inherit from your parents and they from their parents. It's
actually very easy to understand when you can see it graphically, much
easier to understand than trying to understand it from a verbal description.
They explain how autosomal DNA can help you understand both our deep
ancestry and our recent genetic past.
You can see in the video how each child actually inherits a rancom
combination of the DNA from their 4 grandparents. The key words here are
random combination. In each of the parents, they have DNA from their parents
and they can only pass on half of that to each child, so it's randomly
combined to form just enough to pass on to a child. Each child gets a
different random combination from their parents. Think of 3 different card
decks being shuffled. None of the three will be in the exact same order, but
they will indeed all have the same cards as members of the deck. If you were
deal only half of each deck, each set cards would include different cards
from the original deck.
Let's talk for a minute about random recombination. We're learning that
maybe random isn't quite as random as we had thought. It has been discovered
that some DNA is passed in groups typically and blocks of DNA are often not
broken up and are passed together. The closer you are related to someone,
the more likely it will be that you will carry some of the same blocks of
DNA that they do. The more distantly related, the fewer blocks you'll have
in common and the smaller those blocks will be. This is one of the ways that
23andMe determines your genetic distance from someone and they classify you
as "close relative", 3rd cousin, 4th, 5th, 6th, etc.
So to answer the original question, three sisters (or siblings) would not
test the same because they would inherit different genes from their parents,
which are actually a recombination of the DNA of their 4 grandparents.
Some portions of the test results you would expect to be more similar than
others.
Health Traits - some of these might be the same, but some might be
completely different as well due to the inheritance patterns.
Haplogroup - mitochondrial haplogroup would be identical assuming the same
mother, Yline haplogroup would be identical for males assuming the same
father
Ethnicity - this is the interesting area where sibling can actually differ
depending on the genes they inherited. One sibling could indeed have
somewhat different results for their percent ethnicity due to the genes they
did, or did not, inherit from their parents/grandparents.
Relative Finder - this should be pretty much the same, but might differ on
more distant relationships due to recombination
In a nutshell, you can't extrapolate the health information of your sibling
to be your own because you inherit differently from your parents. You can
extrapolate some of your ancestry information to be the same as your own,
but not all of it. I think it would be very interesting to compare the
results of a number of parent/child and sibling tests to see how well
23andMe does in their Relative Finder predictions.
Roberta Estes



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