Monday, 13 May 2013

Step 3.3 - eliminating lines of unlikely ethnicity or nationality

Can you rule out certain ancestral lines on the basis of ethnicity or nationality?

This technique is not as foolproof as the ones previously discussed but it can certainly help you further narrow down your list of possible candidates for Common Ancestor. It works particularly well if you or your match have ancestors from a variety of different countries. For example, in my own family tree, all my ancestors are Irish (as far as I know). There is the possibility that if I went further back I might find some English, Welsh or Scottish ancestors too, but it is far less likely that I will discover Chinese or African ancestors within the last several hundred years.

Having said that, my ethnic admixture results from 23andMe reveal that I am 99.8% European and 0.1% Sub-Saharan African so this suggests that perhaps 1 of my 1000 or so ancestors (at the level of my 8x great grandparents, born about 1600) was African. So you can never be sure what awaits you in the unknown generations further back from where you have currently managed to extend your tree!

Nevertheless, I can be reasonably certain in suggesting to all my matches that any Common Ancestor that I share with them is likely to be Irish. As a result, they can focus their attention on any Irish lines in their own family tree. I'm not confident enough to say to them that they can eliminate any non-Irish lines from further consideration, but I can certainly say that the "balance of probabilities" sways more towards the Irish lines and more away from the non-Irish lines in their tree.

This could be given further credence by demonstrating that the segment of DNA on which we match is more likely to be Irish / European, rather than Asian or African (for example).

In her blog entitled X Marks the Spot, Roberta Estes uses an example from her own family to demonstrate the practical application of X-chromosome inheritance in combination with ethnicity and nationality analysis to narrow down the number of potential ancestral lines on which the Common Ancestor sits.

A Worked Example

Using the previous example of my aunt JH and MB, we were able to shortlist the potential ancestral lines to those marked with a red X (because JH & MB match each other on the X-chromosome). However, it is clear from MB's Bow Tie chart that her 3 specific ancestors 29, 30 & 31 are English, and therefore, while it is not possible to rule out these ancestral lines completely, it certainly points us away from these lines as potential candidates and draws our focus onto the other shortlisted ancestral lines (26, 27, and 21, 22, & 23).

Links, Reources, & Further Reading

Roberta Estes combines a variety of the techniques we are discussing to narrow down the list of potential candidates for her Common Ancestor in Revealing American Indian and Minority Heritage Using Y-line, Mitochondrial, Autosomal and X-Chromosomal Testing Data Combined with Pedigree Analysis. This article was published in JOGG (the Journal of Genetic Genealogy) Fall 2010, Vol. 6, Number 1, pp1-37.

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