Joint Matches - Triangulation
Your have one-to-one matches but it is possible that you both match another person. If all three of you match in the same place on the chromosome then you could be from the same original family. The significance of this is would be that all 3 of you have the same common ancestor line - for example you may relate to the father of the family and two others may relate to different children.
The caveat here though is that you have two chromosomes and may match on different copies of the same numbered chromosome? Then the scenario would be that your two matches are from different sides of your family OR you could both match on different sides of their family?
If the three of you match on the same place of the chromosome, there is a better chance of finding the area of investigation for a common ancestor. This is a cluster and a cluster can include many people and more people = more clues and easier work? The segments do not have to be exactly the same length but ideally be very similar overlaps as in the example below.
Website tools use the top 100 or 500 matches and tests them against each other. Where it finds all the people who triangulate at the same part of a chromosome it will make a group. Each cluster represents one area or branch of your tree and all the people in the cluster got their DNA from the same ancestor or ancestral branch. However, that can be a lot of people to write to. Take the biggest group or the most interesting and start there. For people who were adopted or have unknown lines and ethnicities this tool can help you work toward those goals.
Sometimes your research suggests a DNA match should exist between you and someone else but no match is found? Then you need to see if there is an intermediate match. GedMatch provides a tool for this and your DNA testing host probably has one too by now. MyHeritage calls it 'Shared Matches' and 23andMe, 'Relatives in common'. If you contact the intermediate and share notes and stories it is possible to narrow down the connections of how the three of you are related by surnames, geography and timelines.
GedMatch does this for you as do other sites. Put your kit number and the other persons DNA into the "People Who Match both of 1 or 2 Kits Tool" and it will generate a list of any third party DNA matching both of you and the other person, from the millions of members.
Please note that It will also give you contact details to enable you to write and introduce yourself. BUT before you do that, you MUST take each kit number of interest and run a one-to-one test to make sure that the result is true!you and use them as your focus. You may note an ethnicity or a common surname of particular interest in their cluster or profiles?
This site aims to be complimentary to other sites with similar aims.
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