Generations and Ethnic Percentages

Genetic genealogy is the application of genetics to traditional genealogy. Genetic genealogy involves the use of genealogical DNA testing to determine the level and type of the genetic relationship between individuals.
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darkerhorse
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Generations and Ethnic Percentages

Post by darkerhorse »

My understanding is that since we have 128 5x great-grandparents, you'd expect to inherit about 1/128 or 0.78% of your DNA from any given 5x great-grandparent.

Now, if a given 5x great-grandparent was the only one of your direct ancestors with , say, North African ancestry, and he was full-blooded, then you can expect to have 0.78% of your DNA to be North African (in a perfect world).

Is that correct?

If this example applied to two 5x great-grandparents who were each full-blooded then the expected percent North African would be double, to 2/128 or 1.56%^.

Is that correct?

I suspect my father's family has North African blood on his father's maternal side but no one in the immediate family has taken a DNA test, and I wanted to know what percentage to expect, were it to be true. The paper trail shows no evidence of anything but pure Sicilian ancestry, and it ends at about the 5x great-grandparents. So, I figure, if there was a full-blooded North African then he/she would have to be beyond that generation.

Would only 0.78% or 1.56% North African likely show up or be reported on a DNA test?

I would add that many Sicilians have some North African ancestry but my suspicion is based on looks, which I know is unreliable. I'm just wondering if DNA testing would even pick it up if it's that far back.
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MarcuccioV
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Re: Generations and Ethnic Percentages

Post by MarcuccioV »

The way I understand it, in mathematical theory, yes, but in reality it doesn't work that way, as siblings can get various percentages of DNA from the same parents, altering there ethnic makeup from each other. I guess you'd call it a "crapshoot". Just like the pic you posted of the 3 brothers; each looks different & likely has different percentages in their DNA makeup.

I've even read where one can receive DNA from 3 grandparents, but not the 4th. It's completely random...
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MarcuccioV
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Re: Generations and Ethnic Percentages

Post by MarcuccioV »

This MIGHT help to explain it a little better. The science is a little bit above my pay grade...

https://www.ancestry.com/cs/dna-help/ma ... 20you%20do.
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darkerhorse
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Re: Generations and Ethnic Percentages

Post by darkerhorse »

Yeah, I was just looking for the theoretical percentage, to see if it was expected to be large enough to show.

I suppose it's a crap shoot in any one case, but over infinite cases the average percentage should approach the number(s) cited above.

At the 5x great-grandparent generation, it might be a needle in a haystack (which would have been a better title for this thread).
darkerhorse
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Re: Generations and Ethnic Percentages

Post by darkerhorse »

In other words, in this example, North African ancestry may very well not be detected by DNA testing, even if it were in the family tree.
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MarcuccioV
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Re: Generations and Ethnic Percentages

Post by MarcuccioV »

darkerhorse wrote: 09 Apr 2021, 01:28 In other words, in this example, North African ancestry may very well not be detected by DNA testing, even if it were in the family tree.
That would be the short answer, yes...
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Re: Generations and Ethnic Percentages

Post by perhaps »

my Italian Sicilian friend tested with myheritage and has this percentage: 47% Italian; 28.5 % greek and south Italian, 10.7% sephardic Jewish-North African, 5.1% North African, 8.3% other: that is: 4.8% w Asian, 1.3% ashkenazi Jewish, 1.2% Nigerian, and 1.0 % melanesian. as he said: some of everything! he is 92 yr old this year.
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amis89
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Re: Generations and Ethnic Percentages

Post by amis89 »

You can inherit more ethnic dna from one ancestor and less from another. My mother is half Italian, so I should be something around 25%, but when I add up all of the percentages that come from southern Italy (middle eastern, Greek, Sardinian, etc.; I come out to have approximately 35% “Italian” dna. My full sister ended up with less than 20%.
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