In Module 1 of 'Understanding DNA Basics' we discussed the key concepts and theories relating to DNA analysis for genealogy. Before moving to Module 2, make sure you understand the theory of segment triangulation. By now you should have completed the exercises to understand the difference between 'shared matches', 'shared segments' and 'triangulated segments'.
This post is aimed to prepare you for examining the 'shared segments' of a known match and to drill down to identify more distant connections and push the segment further back in your pedigree.
The goal for Module 1 is to examine all the 'shared matches' between you and your known match and to identify those who also share 'triangulated segments' with you and your known match. That is, all three of you match each other on the same chromosome, in the same segment location.
EXERCISE STEP 1:
* First, identify a close match on the line that relates to the one you need to investigate to achieve your identified DNA goal. We will call this match - Target 1;
* If you have a number of relevant kits, use the oldest person who is likely to have the most DNA inherited from the target ancestor;
* Do a 'one to one' (position only) between yourself (or the oldest ancestor on your identified line to the target ancestor) and Target 1. The result should look something like this:
EXERCISE STEP 2:
* Work though the list as we did in the previous post, to identify matches who share on the same segment location for each chromosome. In my example this would be Chromosomes 4, 16 and 19.
EXERCISE STEP 3:
* For those matches who triangulate with yourself (or the oldest ancestor on your identified line to the target ancestor) and Target 1 on each chromosome, they each form specific 'triangulated segments'.
* You may have a number of matches who appear to match yourself (or the oldest ancestor on your identified line to the target ancestor) and Target 1. For these matches we now need to do 'one on ones' to ensure that every match matches everyone else who matches in the same 'segment area'.
* If everyone matches each other, they form what is called a 'triangulated group'.
* Identify the number of matches for each potential 'triangulated group'. For me, I should have at least three groups one on each of the chromosomes 4, 16 and 18. If your segments are long, there may be more than one triangulated group on the length of the segment location on the chromosome where you and Target 1 match.
REMEMBER: We are doing these exercises manually, which is the long way, so that you understand the analysis process. In later modules we will discuss quicker ways to get the same information.
EXERCISE STEP 4:
* Generally, the next step in the process is to interrogate each of the matches in the 'triangulated group' (TG) to find an MRCA and to push back the segment a further generation. Everyone in the segment 'triangulated group' will share a common ancestor. The segment could go back many generations, or the match could fit in even closer to you than the identified MRCA, but still shares the more distant MRCA with others. Our goal is to push back one generation at a time and 'walk back the segment'.
* For Module 1, there is no need to undertake more steps, or interrogate the group. However, for your own research you may wish to pursue your TG to try and find others in the group who share a known MRCA.
* We will discussing triangulated groups in Modules 2 and 3.
* We will return to these matches later in the course.
