Mapping My DNA To My Four Grandparents

I was thinking of calling this Blog “Kathy Meet Kitty“. Kathy is Kathy Johnston who taught me how to map my ancestral segments by comparing my DNA to two of my siblings’ DNA results and determining our crossover points. The crossover points can then be used to map out which grandparent you got your DNA from without having to physically test those grandparents. This is quite convenient as all my grandparents have been gone for quite a while. Kitty is Kitty Munson who has developed a Chromosome Mapper here. I have not seen a blog using Kitty’s Chromosome Mapper to map ancestral DNA segments via Kathy Johnston’s method, so I thought that I would write one. Kathy’s method is posted here.

Two Types of Segments

There are two types of segments, thus at least two types of segment mapping. This concept is best explained at the Segmentology Blog in an article appropriately called, What is a Segment?

ancestral segments

That Segmentology article first mentions ancestral segments. These are the segments that Kathy Johnston knows how to map. I have written many blogs about mapping my ancestral segments using her method. Ancestral Segments are the segments that you actually get from your ancestors. They fill up all your DNA. Here is an example of the ancestral segments that I have mapped to my four grandparents.

Joel Segment Map

Look at Chromosomes 1, 5, 6 and 7 for starters. This shows all my DNA filled in. The 2 paternal grandparents are on the top half of the chromosomes in blue and grean and the maternal two grandparents are on the bottom in red and peach color. The DNA I received alternates between one grandparent and another and fills in all the area. In fact, that is the process of recombination and can be seen in the Ancestral Segment Maps.

shared segments

These are segments that you find at for example. These are our DNA matches. These matches may have a proposed relationship based on how much DNA you and your match share. Here is an example of some of my matches using Kitty’s Chromosome Mapper.

Chromosome map 4 Apr 2016

The best way to fill in a map like this is by testing as many relatives as possible. Now look at chromosome 1, 5, 6, and 7 on the shared segment map compared to the ancestral segment map above. The ancestral segment map on Chromosome 1, for example,¬† shows how much DNA I actually got from my Hartley grandfather. The blue in the Shared Segment Map shows how much I matched my father’s cousin. Next look at the maternal (bottom) part of Chromosome 1. Here the Rathfelder and Lentz matches on the right hand side are filled in on the Ancestral Segment Map. However, there is an additional section of Lentz on the left hand side of the Ancestral Segment Map where I don’t even have a match. I can tell I got my DNA there from my Lentz maternal grandmother. That is due to the crossover points I have and the fact that the DNA you get from your grandparents alternates between grandparent. On the maternal side, the alternation is between Rathfelder and Lentz.

If you find any inconsistencies between my Ancestral Segment Map and my Shared Segment Map, that means I messed up somehow.

More Ancestral Segment Mapping: Sister Heidi

In order to map my ancestral segments, I needed two siblings, so I used my two sisters, Heidi and Sharon. Here is Heidi’s ancestral DNA mapped out:

Heidi Segment Map

A few observations:

  • The areas of pale blue are where I had trouble figuring out how to map the ancestral segments, so nothing is mapped in these areas. I may have mapped out some of the segments, but then had difficulty telling whether they were maternal or paternal due to lack of known cousins that had tested. So I left these areas blank
  • The maternal areas shown as MG1 and MG2 – For these areas, I knew I had two maternal grandparents but I wasn’t sure which was which. Again based on lack of known cousins that had tested. I could perhaps guess, based on actual matches I had in these segments or where those matches were from, but I noted where the crossovers were and left these grandparents un-named.
  • These unknown grandparents are consistent within each chromosome and each sibling within each chromosome, but they are not consistent between chromosomes. So the unknown MG2 in Chromosome 8 may not be the same MG2 in Chromosome 11.
  • In my (Joel’s) Ancestral Segment Map, I don’t show any DNA on my paternal side for the X Chromosome. That is because males don’t get an X Chromosome from their father.
  • Heidi shows that she got her paternal X from her dad’s mom – a Frazer. Further, that chromosome did not appear to recombine. That means that she got that whole chunk from one of her great grandparents on the Frazer side.

How Do You Know What You Are Finding If You Don’t Know Where To Look?

These maps are very helpful in showing you where to look for DNA. Many people have matches that have ancestral names that are¬†common to us but are not related. For example, my mother has matches with people that have Fraser or Frazer ancestors. I am related to Frazer on my father’s side. That means that I can forget about following up on maternal Frazer matches.

  • If I do want to look for Frazers, I need to look in my green areas (or my sister’s green areas) which is on her paternal side.
  • My sister Heidi is in an important Frazer Triangulation Group on her Chromosome 1 on the right hand side. She triangulates with others in a Frazer DNA Project I am working on. I am not in that group. Look at my Chromosome 1. It is nearly all covered by Hartley DNA. That explains why I don’t match these other Frazers at standard thresholds.
  • What if we were to want to look for Lentz ancestors of Heidi? We need to look at the red areas. Chromosomes 1, 6, 9. 14, 20, and 22 would be a good place to look. Fortunately, I also have Heidi’s matches on a spreadsheet. They are mostly divided by maternal and paternal matches. My mother has been tested for DNA. Based on that, I have Heidi’s phased maternal and paternal results and her matches to each of those results using

Finally Sharon

My sister Sharon completes the Ancestral Segment Mapping:

Sharon Segment Map

  • The autosomal DNA that is missing on Sharon’s Map is the same for her 2 siblings. This is because Kathy Johnson’s ancestral segment mapping technique compares the siblings to each other using the chromosome browser.
  • Sharon has a lot of Frazer DNA match potential at Chromosomes 1, 8-12, 15, and 22.
  • However, Sharon is also not in the Frazer Triangulation Group in Chromosome 1 on the right hand side. In that particular section, she got her DNA from her Hartley paternal side.
  • The above point shows why it is important to test siblings.
  • Heidi and Sharon both have a large match (50+ cM) with someone on their X Chromosome. This person also has autosomal matches with my sisters and others in the Frazer DNA project.

Summary and Observations:

  • Ancestral Segment Mapping can be useful in determining which grandparent your matches match.
  • I know already whether my matches are on my maternal or paternal side. However, this goes back one more generation and further sorts my matches to grandparents. This cuts down the guessing by another half.
  • The maps also point out the areas where you can’t be as sure as to which grandparent your matches match as those areas are not mapped yet.
  • Ancestral Segments should line up with Triangulation Groups
  • Ancestral Segment Mapping can show matches that are Identical by Chance (IBC) or false matches.


4 Replies to “Mapping My DNA To My Four Grandparents”

  1. This makes absolutely no sense to me. You have told what you’ve found, but I don’t see any explanation as to how to find it. I need a step-by-step process, like a template that I can plug my information into.

    Sorry, I’ve got a graduate degree and all this dna sorting makes me feel stupid.

    1. There are a few tips.
      1. Start with the shorter Chromosomes.
      2. Lower the gedmatch thresholds to try to see what is going on.
      3. Occasionally tips will show up on Facebook.
      4. If you keep a spreadsheet, check your matches and Triangulation Groups. A match or Triangulation Group should not go through a crossover.
      5. Sometimes people who enjoy looking at crossovers may look at your particular situation to give some help or advice.

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