Re: Triangulated DNA matches and Pile-up Areas #dna


Adam Cherson
 

Lee,

I'm not a 'degreed' geneticist but have been working as a private researcher for many years. What I am about to say is only my perspective based on experience. In addition to the possibility of pile-up zones, there is another aspect and that is the length of and number of triangulating segments. In your example I see a 6.6 cM segment and do not know whether this is the only one for the group.

My view is definitely in the 'more is better' camp. In my work I tend to disregard anything under 7 cM and especially if it is the only triangulating segment for the group.This is all the more so when one considers that many of the chip-reading programs use something called imputation, which is in effect a way of filling in gaps between segments to make them appear longer.

As with all genetic analysis I feel much more secure when triangulation results are supported by other evidence, both genetic and non. For example I tend to be accept smaller triangulation segments when the overall amount of matching is consistent with the degrees of relationship I am trying to prove for the various group members.

Genetic analysis is often somewhat impressionistic and I don't think anyone can say for sure that this or that segment length is or is not significant. I look at your example this way: if you remove the pile-up zone from consideration, you have a triangulation of about 2.4 cM, which is below what most people, including myself consider significant. Therefore, if this is your only evidence of common ancestry for the group I wouldn't consider this result as proof. If it is only one of several other types of evidence then it could lend a tiny bit of support to the hypothesis.

There is a blog and discussion dedicated to segment analysis which may discusses such matters as segment length and pile-ups in greater detail and may provide you with valuable information: https://segmentology.org/ You may want to re-post your question there for additional opinion and discussion.

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Adam Cherson

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