Author Topic: Comparing DNA - GEDmatch  (Read 697 times)

Offline colmc

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Comparing DNA - GEDmatch
« on: Saturday 27 January 18 22:02 GMT (UK) »
Quick question.
I've only recently started comparing DNA, and so far i've been using an excel page to chart and cross reference matches. Am I right in thinking that if my relatives DNA matches with person one and tells me that, for example, it is chromosome 5 and starting and finishing at 38,000,00 and 65,000,00 .. If person one matches with person two also on chromosome 5 starting at 41,000,00 and finishing at 73,000,00, does that mean that the shared DNA between persons one and two is from the same common ancestor as my relatives, and that if the others are matching on a different range or chromosome that they share DNA from elsewhere that is not common to my relative.
hope my question makes sense.

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Offline colmc

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Re: Comparing DNA - GEDmatch
« Reply #1 on: Sunday 28 January 18 04:22 GMT (UK) »
Will try to clarify later

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Offline Eric Hatfield

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Re: Comparing DNA - GEDmatch
« Reply #2 on: Tuesday 30 January 18 00:52 GMT (UK) »
There are two sides to our DNA, so if two people match a third person on the same segment, it is possible they match on different sides, and may not necessarily be related. What is needed is to "triangulate", where each of the three people match each other, then we can be confident that they all match on the same side, and so are related.

Offline colmc

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Re: Comparing DNA - GEDmatch
« Reply #3 on: Tuesday 30 January 18 19:29 GMT (UK) »
Thanks Eric.
Sorry I knew I wasn't clear somewhere. As I add new DNA kit numbers to the sheet I am comparing them to my relatives and to all the other ones, which have previously been compared to my relatives and to each other. I am highlighting the cell where they match in a colour code to indicate matches that are not on the same chromosome and range as being another connection between them, and one with a common chromosome and range as being the same common ancestor, and then further colours where I think I know which line that common ancestor is on.
So do you think I am making the correct assumptions with what I am doing?

Offline Eric Hatfield

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Re: Comparing DNA - GEDmatch
« Reply #4 on: Wednesday 31 January 18 01:17 GMT (UK) »
I am not an expert, but I think that is the right approach. But until you can triangulate, the matches on the same segment are only POSSIBLY related to each other - some will be some may not be.

If you have access to two test results, you and a known relative, you can test each match against both of you and that way triangulate. If you don't have access to a relative's result as well as your own, you can ask each match whether they match the others and get your triangulation that way. I have found this to work, because people tend to want to help each other because it helps themselves, and sometimes you can find a whole group who are related and keep each other informed.

Offline colmc

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Re: Comparing DNA - GEDmatch
« Reply #5 on: Wednesday 31 January 18 01:41 GMT (UK) »
Thanks Eric