My Father In Law’s Grandparents’ DNA

In this Blog I will use a technique described by Kathy Johnston to look at some of my father in law Richard’s DNA. I will map out his 4 grandparents on Chromosome 15. These would be 4 of my wife’s great grandparents. Then I will try to figure out which grandparent goes with each segment of the mapped Chromosome.

My Father In Law and His Two Sisters

The mapping technique requires 3 siblings. My father in law tested at FTDNA and his two sisters tested at AncestryDNA. I have those results and have uploaded them to

fully identical and half identical

In the first step, I compare the 3 siblings to each other using using their chromosome browser. Here is how Lorraine and his brother Richard (my father in law) match each other at on Chromosome 15. I chose this chromosome because it is one of the smaller chromosomes, hence easier to map. Also I already knew there were some other cousins on Richard’s maternal side that had tested and had fairly good results with Richard on this Chromosome.

Lorraine V Richard
Lorraine V Richard

As shown in the above, Lorraine and Richard have one long match on Chromosome 15. I will use locations in millions, so I’ll say the match was from 18 to 94. This is represented by a sold blue line. According to FTDNA, the area before 18 is a SNP poor area not used for comparisons. The solid green sections are where Lorraine and Richard share the same DNA from 2 of their grandparents. These would be one maternal grandparent and one paternal grandparent. The green is also called a Fully Identical Region or FIR. The yellow area is called a half identical region. This means that Richard and Lorraine share the DNA from one maternal or paternal grandparent. The red area with no blue line below it is the area where Richard and Lorraine don’t share any DNA. However, this information is actually quite helpful. This would mean that if Richard got his DNA in this segment from his Paternal Grandfather and Maternal Grandmother, that Lorraine’s DNA would have to be from her Paternal Grandmother and Maternal Grandfather, for example. There are only 4 choices, so process of elimination can be used.

Comparing three siblings at a time

Next I line up the results of the three siblings.

Chr 15 3 siblings

I am now looking for crossovers. This is where Richard’s DNA, for example, switched from being inherited from one grandparent to being inherited from another grandparent.

Chr 15 with crossovers

Next I look down every line to see who owns each crossover. Let’s just look at the first vertical crossover line. In comparing Lorraine V Richard, nothing is changing there as there is green on either side of the line. At Lorraine V Virginia, and at Richard V Virginia, there is a change from no match to an HIR. The one in common in those 2 changes is Virginia. So she is the one that owns the first crossover point. That means at that point (to give a number would be 27) she received her DNA from one grandparent to the left of that point and she received her DNA from another grandparent to the right of that point. We don’t know which grandparent, or whether it was on her maternal or paternal side. We do know that both grandparents on either side of the crossover are either maternal or paternal grandparents. That fact will help me as I try to figure out which grandparent Virginia got her DNA from.

Assigning crossover points

Here we will give a name to each crossover point. We are building a DNA skeleton or frame for each person so to speak. These are assigned by each persons’ initial at the bottom of each vertical crossover line below.

Assign Names to Crossovers

This tells us that there are 7 crossovers for the 3 siblings. Virginia has 3 and Lorraine and Richard have 2 each.

The chromosome map

Next I will build a Chromosome Map based on the above information. This map will be for the 3 siblings and have a maternal and paternal side with 2 grandparents on each side. [That should make sense as you think about your own family situation.] To begin with, these grandparents will be represented by 4 different colors as we won’t know which grandparent is which. Here is the bare bones skeleton:


I kept the crossover designations on each of the vertical lines. I’ll add the 3 chromosome maps to the right of the L, R, and V on the left side for Lorraine, Richard, and Virginia. On the bottom, I have the locations on the chromosome for each crossover point. I am missing a location for the next to the last crossover line. This could be guessed or estimated based on where Virginia’s actual crossovers are later. By eye it would be about 90.

Let’s map it

Assign Names to Crossovers

I could start with any area, but I’ll start with the top left. This is the green FIR match between Lorraine and Richard. Fully identical means they both received the same DNA from the same 2 grandparents. Those 2 grandparents were one from the mother’s side and one from the father’s side. Those will be represented by green and blue.

Chr 15 First FIR

Lorraine will have one crossover preventing one of her lines (colors) from extending beyond her crossover further to the right. Richard has no crossover at this point, so his two grandparents’ DNA can extend to his ‘R’ crossover line. Meanwhile Virginia doesn’t match at either grandparent in this area, so we need to give her 2 different colors representing the DNA she got from her 2 other grandparents.

Chr 15 part 2

Due to the place I started, I’m stuck already – at least on the FIRs and no matches (green and red sections of the chromosome map).

Assign Names to Crossovers

The next step is to map an HIR. As HIRs are more ambiguous (one matches and one doesn’t) I only get one shot at guessing. Once I make one guess, then this locks in the grandparents and no further HIR guessing is allowed. Our choices for HIRs are between 27 and 35. I’ll choose Lorraine V Virginia. They are HIR between 27 and 31.

Chr 15 part 3

Now comparing L and V from 27-31, I see that their 2 green segments match and their blue and purple segments do not match. This was my one chance at guessing. I could have guessed the other way around and it wouldn’t have mattered, but at this point the colors are locked in and no more guessing is allowed. Next, Virginia has no crossovers for a while, so I’ll extend the DNA she got from her green and purple grandparents to the right to her next crossover point.

Chr 15 part 4

Next I notice that Virginia has no match with Lorraine from 31-46 and no match with Richard from 35-60. That means that Lorraine and Richard got their DNA from the opposite grandparent on their maternal or paternal side. So far, everything is relative, so the top orange and green may be maternal or paternal. We don’t know yet.

Chr 15 part 5

Scanning up from Virginia’s Chromosome 15 map from location 35 to the right, we see that Richard and Lorraine have the opposite colors. That corresponds with the no match comparisons we had in the gedmatch comparisons. We would be stuck here except for the fact that on Richard’s bar, he has no crossover at location 60. [That crossover at 60 belongs to his sister Virginia.] That means that the DNA that he got from his orange and blue grandparents can extend to his next crossover at 95.

Chr 15 part 6

Assign Names to Crossovers

Now we again are almost stuck, except that Richard and Virginia have a green FIR from 90 to 95.

Chr 15 part 7

We can then extend Virginia’s grandparents’ DNA to the right.

Chr 15 part 8

Assign Names to Crossovers

Now we truly are stuck. We only have HIRs left and I already used my one guess for those. There is a no match between Lorraine and Richard on the right hand side, as we have no DNA to go against after 95 for those 2.

Cousins to the Rescue

There is one more way to fill in these segments. That is with the matches from actual cousins. We will want to figure out which grandparents these segments go to if we can anyway by using cousin matches. First, let’s look a little at the genealogy of the cousins that have tested.

Pouliot LeFevre Diagram

In the bottom box is Richard, but I should have included his sisters Lorraine and Virginia there also. These siblings have 4 cousins that have tested on the maternal LeFevre side. Here I got a snapshot of Estelle LeFevre (b. 1905) while getting DNA from Virginia:


There are 2 testers descended from the Pouliot Grandfather. The other 2 testers are descended from Pouliot and LeFevre. I discussed the issues in separating the DNA from those two ancestors in my previous Blog.

Pouliot LeFevre Diagram rev

Here are the 3 siblings as they match their reference cousins. The more important cousin, in a way, is Fred as he descends from the Pouliots and not the LeFevres. Note that there is no overlap between Fred versus Patricia and her brother Joseph in each comparison. That is where the crossover is occurring between the Pouliot grandparent and the LeFevre grandparent. Now for each sibling (Lorraine, Richard and Virginia) that crossover is at a different location. For Lorraine, it is at 31. For Richard, it is at 35. For Virginia, it is at 28. Now refer to the second image below. The place where all those maternal crossovers occur is on the top row of each bar between the orange and green segments.

3 sibs on Chromosome Browser to All

Chr 15 part 8

So for this try, the green represents the DNA that the siblings Lorraine, Richard and Virginia got from their Pouliot grandmother and the orange represents the DNA that each sibling got from their LeFevre grandfather.

Just to confuse things – a completed chromosome 15 map

Here is a completed Chromosome 15 that I did previously. In the version below, I started more on the right and worked my way to the left. That left blanks on the left that I was able to fill in by the actual cousins. Note that the colors are relative and are reversed for the Pouliot and LeFevre grandparents which I have labelled on this Chromosome Map:

Completed Chromosome 15 Map for 3 Siblings
Completed Chromosome 15 Map for 3 Siblings
what about the paternal side of the map?

The paternal side is mapped out, but I have no reference testers. These testers would ideally be 2nd cousins that are related on only one paternal line. I only need one of these 2nd cousins to identify one grandparent. Then the leftover grandparent belongs to the other side due to process of elimination. There are already likely people that have tested at AncestryDNA, but due to lack of a chromosome browser there, I don’t have where the matches are. For now I will leave them as colors or I can call them paternal grandparents 1 and 2. The actual paternal grandparents are Edward Butler (b. 1875) and Lillie Kerivan (b. 1874).

My Wife’s DNA

The DNA represented in the map above comes from my father in law’s grandparents. However, for my wife, this represents the DNA that she got from 4 of her paternal great grandparents. How could I map that out for her?


The short and simple answer is this: My wife got her DNA from her 2 parents. That is a given. So she, like her father, Richard, has a maternal and paternal side. She will have a similar map as her father. However, now her paternal side will have her father’s 4 (or in this case 3) grandparents all on one chromosome. To make room, something has to give.

Completed Chromosome 15 Map for 3 Siblings
Completed Chromosome 15 Map for 3 Siblings

Here is Richard on the middle line. Note that he only received DNA from one of his paternal grandparents. As my wife got all her paternal DNA from her father (sounds obvious, but still worth stating), she will potentially only get DNA from 3 out of 4 of her great grandparents. Here I am borrowing a Figure from a very helpful blog called Segments: Bottom-Up:

segments greatgrandparents

In that Segmentology Blog, Chromosome 5 is used as an example. Here all the great grandparents are represented. Unfortunately, I have not tested 2 of my wife’s siblings. If I had, then I would have the first line which indicates her grandparents (in this case on her paternal side). The second line of the image above, shows in a generic way, the new crossovers that my wife could have for her great grandparent level.

My wife and her 2 aunts

Here is how my wife looks compared to her 2 aunts at gedmatch compared to those Aunts’ Chromosome 15 map. I won’t show the match to her father as she matches him in all places.

Marie Chr 15

Completed Chromosome 15 Map for 3 Siblings

From this, I take away that my wife matches her 2 Aunts on their maternal side. The gedmatch match between my wife and her Aunt Lorraine shows a break at 31 which corresponds to Aunt Lorraine’s maternal side. Likewise my wife’s second match with her Aunt Virginia starts at 60 which corresponds with Aunt Virginia’s maternal start of her switch from Pouliot DNA to LeFevre DNA. When I merge these 2 results together, it looks like the Chromosome map for Richard, above with a crossover break at 35. This makes sense, as my wife got her paternal DNA from her dad. If I was making a Chromosome map for my wife, it would include her 2 great grandparents: Martin LeFevre b. 1872 and Emma Pouliot b. 1874. Her Chromosome 15 Map would look like her father’s up to location 95. After that point it may also be the same as her father’s, but I don’t believe that I can prove that.

It is beginning to look like there may have been no recombination for my wife on Chromosome 15. So far, we have not seen any room in Marie’s DNA for the purple paternal DNA that I mapped out for Richard above.

Enter cousin John

Recently, my wife and I contacted her cousin John at AncestryDNA. He kindly uploaded his DNA to gedmatch. I said that I would use his DNA for research. Then I thought, “Now how am I going to use his DNA for research?” Here is one way. We will look to see how cousin John matches his Uncle and 2 Aunts at Chromosome 15.

John Chr 15

These red and yellow show us that Cousin John likes to eat at MacDonalds. Not really. It does show:

  • coverage of the entire Chromosome 15 from position 18 to 100.
  • one large match with Richard. This would correspond to Richard’s paternal (Irish) side
  • the match with Lorraine could correspond with her paternal side also in the purple area on my Chromosome 15 map above.
  • The 2 matches with Virginia could also be on her Paternal (Irish) side in the blue and purple segments
  • If I were to make a Chromosome 15 map for cousin John, it would be more complete than my wife’s. It would be filled in with 2 great grandparents on his father’s father’s side.

I think I will make a great grandparent Chromosome 15 Map for my wife and her cousin John, but only because this is my 50th genetic genealogy blog. This map will just be for my wife and cousin John’s Paternal side of their Chromosome 15.

Map John Marie

It is a somewhat unusual chromosome map as there are only 2 great grandparents mapped for each cousin. My wife inherited the DNA from her dad’s maternal grandparents¬† Her cousin John inherited his DNA from his dad’s paternal grandparents. The part in the upper right corner should probably been left blank as I have only implied Pouliot DNA there.

further deductions

I have shown that it looks like my wife matches her dad on his Maternal Side. It looks like my wife’s cousin John matches his Uncle and 2 Aunts on their Paternal sides. Remember, I am talking about great grandparent matches, so I am going back a bit. The question is, should my wife match her cousin John on Chromosome 15? I would say no. Let’s look. Here is my wife’s matches in the area of Chromosome 15 down to a level of 3 cMs:

Marie and John

As you can see, there is no Chromosome 15 match. From that I can imply, but not prove, that my wife’s Chromosome 15 after position 95 is the same as her father’s and that she inherited her father’s mother’s Chromosome 15 intact.

To Recombine or not to recombine?

The smaller Chromosomes have less of a chance of recombining.¬† Chromosome 15 has 100 cMs which means on average there should be exactly one crossover per Chromosome 15. Lorraine had one crossover on each of her Chromosomes 15 (maternal and paternal). Richard had 2 maternal crossovers and no paternal crossover so he meets the average. Virginia was an overachiever with 2 maternal and one paternal crossover for an average of 1.5 crossovers. My wife’s father inherited his father’s Chromosome 15 intact, so had no recombination there. Likewise there may have been no recombination from Richard down to my wife on this chromosome.

Summary and Conclusions

  • Kathy Johnston’s method of DNA analysis worked well on my father in law and 2 siblings to find the DNA they inherited from their grandparents who were born between 1872 and 1875.
  • This method worked especially well for the maternal side as there were reference points aka my father in law’s maternal cousins who had tested for DNA. For these segments with matching cousins, I could assign specific grandparents which contributed to my father in law and 2 siblings’ DNA.
  • The segments that my father in law’s family inherited from their grandparents’ Paternal Irish side is defined and in place. However, those segments are awaiting specific names. Once further testing is done or existing testing is uploaded to, then these names should be made clear.
  • This exercise on Chromosome 15 may be repeated for the other chromosomes.
  • This exercise showed two instances where recombination did not take place and another instance where it probably did not take place.
  • I would know more about my wife’s DNA if I had 2 more siblings’ DNA results.
  • I have been neglecting my wife’s DNA results as I had other test results from her older relatives. I need to update her FTDNA and matches. This may give more clues on how she inherited her great grandparents’ DNA from her father.
  • A cousin who has tested was used to triangulate between the 3 siblings and my wife to check the work.
  • Based on the results of the 3 siblings Chromosome Mapping, maps can also be made for the children of these siblings. For the children, the mapping would show which great grandparents they received their DNA from.

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