In Module 3 of 'Combining genetic and genealogical research' we discussed ways to work from your chromosome data to maximise your chance of finding your MRCA. The purpose of undertaking this exercise is to consolidate your understanding of the principles and processes we discussed and to prepare for our next workshop. By examining results at all DNA sites and working between them, you will increase your knowledge of specific segment areas which may lead to more successful outcomes.
So far in the course, we have completed a number of exercises where we identified confirmed and triangulated segments in our genome. We may have identified the shared common ancestor for some of these, or at the very least identified a side or likely ancestral couple based on others sharing in each triangulated group.
- Module 1 - Identifying the triangulated segments of an unknown ancestor - GEDmatch
- Module 1 - Identifying the segments of a known ancestor - GEDmatch
- Module 2 - Identifying triangulated segments and groups - My Heritage (downloads)
- Module 2 - Identifying triangulated segments and groups - Pedigree Thief
- Module 2 - My Heritage Cluster report
This activity aims to help you visualise the segment analysis you have undertaken so far and map your known 'confirmed' and 'triangulated group' segments. There are many approaches to creating chromosome maps, this is just one way to help you get started.
By now you should understand the theory behind two sides to every chromosome, including how to identify triangulated segments and groups. You should also have decided upon your method for retaining details of the DNA matches you have researched, the segments they match on and the results of your analysis, to avoid rework and improve your productivity. Practice reviewing clusters of shared matches to identify triangulated segments and complete this exercise to start to build a chromosome map.
EXERCISE STEP 1:
- Create an account at DNA Painter. A free account allows you to develop one chromosome map.
- Choose the best candidate to map for your current research. Ideally, map yourself, or one of your parents;
- Familiarise yourself with DNA Painter and concepts of chromosome mapping. Suggested resources include the DNA Painter Blog and this 'free' introductory Webinar.
EXERCISE STEP 2:
- Decide how you are going to map your segments, I favour mapping confirmed segments to the ancestor from whom I inherited the segment. Others may choose to map to the parents - ie the ancestral couple. It is a personal choice. The instructions in this blogpost will be to map to to specific ancestor.
- First we are going to identify all our close cousins, up to 3rd cousins, where we have a confirmed paper trail and their total shared segments are within the predicted ranges - AND their match is on a segment data site.
- If you have not already done so, do a 'one on one' with each of them and add the results to your match and segment data lists.
- I would recommend starting at second cousins as they only share one of your grandparent lines and are the most useful.
- Personally, I do not map first cousins because I already have my mother tested, but again this is personal choice. Any segments I share with my first cousins came from our maternal grandparents and from a mapping perspective would just be mapped to my mother, providing limited value. I also find they complicate the map.
- However if you have no parents tested first cousins can be particularly useful to help you determine the sides for your matches and should be mapped to your respective parent.
- First cousins once removed from the older generation may be different. I do use my mothers first cousin on my map, because their segments when mapped are like a second cousin - only inherited from one of my grandparent lines.
- First cousins once removed from the younger generation provide the same information as first cousins and can only be mapped to my mother, so I don't include them for the same reason;
- First cousins, 1C1R and children can be particularly useful for inferred mapping which is a complex technique that we will briefly touch on in Module 4. I prefer to map these segments on a unique map for that purpose.
- Follow the instructions on DNA Painter to map the segments of all your known cousins who meet the criteria in dot point 2;
- You should end up with a map that looks something like this one, it may not look as populated, that will depend on how long you have been researching and the number of matches you have identified at chromosome sites.
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| Example segment map |
EXERCISE STEP 3:
- Make sure you have included all the segments you identified in the Module 1 exercise - Identifying the segments of a known ancestor - GEDmatch;
- As these are all known matches, they all should be mapped to either the maternal or paternal sides and there should be limited ancestor overlap;
- Review the map to ensure that any overlapping segments are coming from the same ancestor, or another further back on the line of the more distant ancestral couple.
- All overlapping matches should triangulate if you have mapped them correctly as they are inherited from the same distant ancestor.
- Depending on how you labelled your matches, when you expand one of the chromosomes it might look the image below. I label my matches to correspond with the MRCA couple and the ahnentafel number of the ancestor who gave me the segment, the match name remains constant. In this case 007 is my maternal grandmother Mona Veronica Murphy, segments inherited from her are labelled in dark green. Her parents are John Murphy and Rebecca Cassidy. I share the MRCA of Murphy-Cassidy with my 1C1R MLAS, however because he triangulates with all my Cassidy-Sweeney cousins in the second segment area, that segment has been mapped as a Cassidy-Sweeney segment and coloured light green to reflect being inherited from my great grandmother Rebecca Cassidy,
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| Expanded maternal segment |
EXERCISE STEP 4:
- Next we are going to map the 'Triangulated groups' we have already identified in each of the previous exercises.
- You will need to have come up with a unique name for each of your groups. In DNA Painter we will map each triangulated group as a 'New Match';
- If we are clear where the segment is coming from, we could map it to the appropriate ancestor - eg. you share the group with a paternal second cousin, so you know the segment was inherited from your paternal grandfather - so we could map the segment to the paternal grandfather. However this may not always be possible and you may need to allocate some groups to 'Both sides' until the MRCA is identified.
- Review the output of GEDmatch exercise from Module 1 Identifying the triangulated segments of an unknown ancestor - GEDmatch and 'Paint all New Matches'.
- Review the output of My Heritage exercises from Module 2 Identifying triangulated segments and groups - My Heritage (downloads), Identifying triangulated segments and groups - Pedigree Thief and the My Heritage Cluster report and 'Paint all New Matches'.
- The example below shows how the segment map might look if you can't allocate sides. Once you determine an MRCA you would then map the segment to the ancestor you inherited it from, ie paternal or maternal.
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| Segments not yet allocated to a side |
As you continue to identify triangulated segment groups add them to this map to keep track of where you are up to. If you use GDAT the segment map will auto-populate, however DNA Painter maps are easier to share with others and there are many other ways you can utilise them.
Over time, as your map populates, it will help you identify possible ancestral lines for new matches and improve your analysis processes. Refer to the Module 3 blogpost for other relevant material.
If you have a paid DNA Painter account you can create more than one map. Now that downloads are available again from Family Tree DNA, why not download your matches and use the Bulk Import Feature at DNA Painter to look at all your matches on one map.
Veronica Williams
Originally published: 6th September 2024
