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dcstep
04-09-12, 23:15
My 1st cousin and I had autosomal DNA tests processed by AncestryDNA.

Here's my geographic report from Ancestry:


Central European 85%

Eastern Euro 15%

Here's John's:


British Isles 64%

Scandinavian 16%

Finish/Volga-Ural 10%

Southern Euro 9%

Unknown 1%


I'm male. My mother and his father were siblings. My mother married a Stephens and his father married a Tuttle. Using traditional geneology, we've traced our common ancestry back to Norman English, Alsace-Lorraine and Germany, with those last two being among the most recent immigrants. The English lines go back into the 1600s.

If autosomal DNA is looking way back to our origins, how can two living 1st cousins have such different geographic profiles?

I've only been able to trace my Stephens line back into the 1800s and he's only been able to trace his Tuttle line back a couple of generations, both lines hit dead ends in the USA.

By the way, we have seemingly valid birth certificates for his father and my mother, showing the same parents, just in case some are wondering. Oh, AncestryDNA correctly identified us as likely 1st cousins with a 99% confidence level.

pipinnacanus
05-09-12, 00:35
Here's my geographic report from Ancestry:
Central European 85%
Eastern Euro 15%


Here's John's:
British Isles 64%
Scandinavian 16%
Finish/Volga-Ural 10%
Southern Euro 9%
Unknown 1%

I'm male. My mother and his father were siblings. how can two living 1st cousins have such different geographic profiles?



You would only be expected to share 12.5% of your genome with a first cousin.
You have 1,024 ancestors in the past 10 generations, and out of these, even a brother or sister from the same parents who are same-sex siblings would only share approx. 50% of their genome.

After about 7 generations, your genetic contribution from any one ancestor starts to peter-out in most cases due to the large number of contributing genetic ancestors.

Your mother and her brother are a generation removed, and are opposite sex, meaning they may only have shared 40-50% of their genome at best, and their respective offspring (you / cousin) are not related beyond the two siblings shared portion of their genomes.

For this reason, at 12.5% avg. shared ancestry between first cousins, its not very surprising to find that your ancestral SNP derive from unrelated source populations.

There is nothing unusual about this if that is what you are concerned about, i can put your mind at rest..

MOESAN
10-11-12, 22:48
You would only be expected to share 12.5% of your genome with a first cousin.
You have 1,024 ancestors in the past 10 generations, and out of these, even a brother or sister from the same parents who are same-sex siblings would only share approx. 50% of their genome.

After about 7 generations, your genetic contribution from any one ancestor starts to peter-out in most cases due to the large number of contributing genetic ancestors.

Your mother and her brother are a generation removed, and are opposite sex, meaning they may only have shared 40-50% of their genome at best, and their respective offspring (you / cousin) are not related beyond the two siblings shared portion of their genomes.


For this reason, at 12.5% avg. shared ancestry between first cousins, its not very surprising to find that your ancestral SNP derive from unrelated source populations.

There is nothing unusual about this if that is what you are concerned about, i can put your mind at rest..



the fact of sharing only 12,5% (approximatively) of common family ancestors doesn't give way to very different autosomals IF your other (not common family) ancestors are from the same close ethnic group... family is not ethny, sometimes new families show more differences (by interethnic marriage) than ancient not related same ethnic members...