How many generations on for a descendant to carry less than 2% ethnicity?

[Abygail]

I'm hopeful that some one is able to help me out with this question.  Approximately how many generations (approximately) from an ancestor of a single ethnicity until a descendant carries less than 2% of that particular ethnicity?  The answer to this will help determine where to look for the mother of an ancestor 8 generations back.  Was he a mulatto or was it his mother?  Or further back?
 

[mckha489]

100%
50%
25%
13%
6.5%
3.25%
1.125%

It’s probably not quite as straight forward as that.
But gives a ball park.

[Abygail]

Thank you for that, it is basically what I was thinking but wasn't certain.  I had thought the following;
Gen 1   1 scot parent    1 other
gen 2    1 scot parent    1 x 50/50 parent
gen 3    1 scot parent    1 x  75/25
gen 4    1 scot parent    1 x  87/13    and so on. 
With us receiving a basic 25% from each of our 4 grandparents we can get a small variation on the 25% but not a huge variation.

[davidft]

a little tool for you to play around with. You can enter either the amount of centimorgans shared or the percentage

https://dnapainter.com/tools/sharedcmv4

[Guy Etchells]

Unfortunately those are the mathematical averages that does not mean that two cousins in the same generation will have the same percentage of DNA form one particular common ancestor.

One may have say 2% of the common ancestor's DNA one may have none of it, even if they both have 2% of the common ancestor's DNA they might not be a match as the may not have the same 2% therefore not match.

We average 50% of each of our parents DNA but siblings do not have the same 50% from each parent, over the generations it is possible not to have any DNA from one ancestor meaning that one would not have any DNA from their ancestors.

Cheers
Guy

[sugarfizzle]

I think people are talking about 2 different things here.

Ethnicity (roots way back, probably beyond paper records)
Autosomal DNA (reliable for only a few generations, e.g. 3rd cousins; small amounts detected for further generations, e.g. 5th to 8th cousins)

The original query was concerning ethnicity, this would be expected to remain for many generations.

As Guy says, we inherit 50% from each parent, but siblings inherit a different 50%. However, this would not impact on ethnicity. Each sibling would inherit the same ethnicity, give or take a few percentage, and this would more or less halve with each generation, but would get very difficult to distinguish  between say 0.125% and 0.625%, 0.3125% etc.

However, at present ethnicity estimations are a very rough tool, not to be relied on, other than to give a bit of 'fun'.

Regards  Margaret

[Romilly]

After the last update at Living DNA, I suddenly acquired 2% DNA from Arabia.

I have no idea where, (or who) it comes from...

Of course, it might just disapear at the next update!

Romilly.

[melba_schmelba]

After the last update at Living DNA, I suddenly acquired 2% DNA from Arabia.

I have no idea where, (or who) it comes from...

Of course, it might just disapear at the next update!

Romilly.

It might be interesting to do GEDMATCH admixture tests if you haven't already, or download Admixture Studio to run several other tests on your computer

https://dnagenics.com/admixture-studio/

If you actually have Arab it will likely be reflected by 'Red Sea' in Eurogenes K13 or K15 tests, but that can also be from Jewish ancestry.

[Romilly]

I'm pretty sure that it's actually Ashkenazi Jewish, melba_scheming.

Living DNA doesn't test for that ethnicity, but I have 7% on Ancestry.

Romilly.