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Puzzled by ethnic breakdown

Replies: 77

Re: Puzzled by ethnic breakdown

Posted: 5 Jan 2013 5:47PM GMT
Classification: Query
You are conflating DNA analysis with the matching algorithm. DNA analysis is in fact completely independent of the paper record. There are two types of matching being done by Ancestry:

1) Biogeographical analysis, which gives you your ethnicity breakdown.
2) Segment matching, which gives you your predicted relationships.

The second of these is done entirely using DNA. What the computer does is identify other people who have tested who share common segments with you. They are looking for individuals who have a piece of DNA of a certain size (at least 5 million base pairs or roughly 5 centimorgans) at the same location (beginning and ending SNPs). Depending on the size and number of matching segments, the computer calculates an approximate degree of relationship--such as sibling, first cousin, 4-6 cousin, etc.

Only after this is done does a separate computer program compare family trees. Ancestry then gives you a list of surnames in your match's tree out to 10 generations (direct ancestral lines only) and identify any surnames that are common to your tree and your matches. It also searches for individuals in both trees that appear to be identical, and marks those with a hint leaf.

So Ancestry doesn't assign people to reference groups based on a paper record, but only on how well their DNA pattern fits with those groups. The connections between individuals are made first through DNA matching, and then subsequently the trees are identified and displayed for you to analyze.

Hope this is fairly clear. It has taken me a long time to understand how all of this works and I learn something new almost every day.

SubjectAuthorDate Posted
jbarry6899 5 Jan 2013 6:18PM GMT 
Sue Coward 5 Jan 2013 8:07PM GMT 
scwbcm 5 Jan 2013 9:37PM GMT 
jbarry6899 5 Jan 2013 10:37PM GMT 
scwbcm 5 Jan 2013 11:40PM GMT 
jbarry6899 6 Jan 2013 12:01AM GMT 
scwbcm 6 Jan 2013 12:16AM GMT 
jbarry6899 6 Jan 2013 12:47AM GMT 
scwbcm 6 Jan 2013 1:10AM GMT 
jbarry6899 6 Jan 2013 1:19AM GMT 
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