Visual Mapping of Butler Chromosome 5 Reveals an Identical By Chance (IBC) AKA False Match

I would like to try to map my in law’s Butler DNA on Chromosome 5. This is based on a rare paternal match that was found at AncestryDNA and cross-referenced at Gedmatch based on similar names and matches.

I have already mapped Chromosome 11 here. I would now like to map Chromosome 5 with the help of one match that my father in law Richard has with a Rooney descendant named Jeanette. That Rooney match is on Richard’s paternal grandmother’s side (Kerivan)

Mapping Chromosome 5

Chromosome 5 is one of the larger chromosomes with 1 being the largest. Now I compare the three Butler siblings: Lorraine; Richard; and Virginia and I add in crossover lines.

I have the locations of the proposed crossovers at the top. Note the smallest match between Lorraine and Virginia. I think that I have the resolution too low for that match, so I will take it out as there is no indication of a change from HIR to FIR (Half Identical Region to Fully Identical Region) or match to non match status in the other sibling comparisons. That will simplify things in the area of 35/38.

Just pretend the match between Lorraine and Virginia at 34 is not there. I will now assign the crossovers to the siblings. The first crossover goes to Richard as he is represented in a FIR (green) to HIR (yellow) change in the 1st comparison and in the HIR to FIR in the 3rd comparison.

The crossover tallies are in:

• Richard (R) – 5
• Virginia (V) – 4
• Lorraine (L) – 2

Actually, I would not be surprised if Lorraine had an additional crossover at the very far right end of the Chromosome, but as it is so small, I am ignoring it for now.

Recall that Richard’s Kerivan Line match was 66-75M. That is probably within the segment R-V ending at 75.5M above. When I compare Lorraine and Richard at full resolution at Gedmatch I get this for Chromosome 5:

This defines Richard’s crossover (from HIR to FIR) and is at about 61M as every ^ is 1M. That means that my assumption about the Rooney/Kerivan match was correct. I am curious to see if I will be able to map the Butler paternal side with just one match.

time to map based on no match, HIR’s and Fir’s

I’ll just start with the large FIR between Lorraine and Richard.

The green FIR above translates to the same blue grandparent DNA on one side and the same green grandparent DNA on the other side for Lorraine and Richard. Then we need to expand these regions of DNA to the crossover lines for Lorraine and Richard:

Lorraine had no crossover to the left to keep her 2 grandparents’ DNA from expanding there. Richard goes to the right to his last crossover. Then we can add in other FIRs and put in opposite colors for the areas where siblings don’t match (red on the chromosome browser above).

This is what I call the Swiss Cheese phase of visual mapping.

comparing gedmatch cousin matches

At this point I would like to compare Gedmatch matches. There is one thing already that doesn’t make sense. According to Gedmatch, Richard has a Kerivan match between 66 and 75M. However, the mapping shows that Lorraine and Richard are in a FIR there. That means that if Richard has this match, then Lorraine should also. Let’s check Lorraine again. I still get no match. When I lower Lorraine’s threshold to 5 cM, I only get a small match with Jeanette on Chromosome 20. That could mean that Richard’s match with Jeanette on Chromosome 5 is by chance. That was disappointing, but informative.

That leaves us the maternal side. Are there matches there?

Here are the matches that I show for our 3 Butler siblings on Chromosome 5. Virginia shows a match on the maternal side with her 1st  cousins Patricia and Joseph (in pink). This could be helpful. But in this case, it appears that it isn’t. That is because in this segment, Virginia doesn’t match her two siblings. Should I give up? I have one more idea. As I mentioned above, Virginia has a maternal match from 88 to 118. However, John matches Richard and Lorraine in that same area. That means that John’s match in that area has to be paternal. John is a nephew, so he shares maternal and paternal matches. Unfortunately, as Richard and Lorraine are FIR in this segment, it tells us no more.

update based on reader comment

I had a comment questioning my apparently too hasty assertion that the John match above (from 81-115M) to Richard and Lorraine was paternal. I did put a little thought into that comment. M MacNeill has kindly phased John’s raw DNA on a different chromosome (Chromosome 1) and came up with this result.

This gets to the old adage about a picture being worth 1,000 words. As John is in a different generation (as is Marie, my wife – his cousin) it gets confusing. However, the above image shows the DNA John got from his four great grandparents on his paternal side.

The segment we are looking at above is between 75.5 and 117. In that stretch all 4 grandparents are represented by four different colors. This is part of what makes the analysis difficult. If there was an HIR in that region, the analysis would have been easier as there would have been only 3 grandparents to consider in that segment.

We know that John matches Virginia on a maternal match, but we don’t know which grandparent it represents. That leaves one other maternal grandparent and two paternal grandparents (from the viewpoint of the above map). John’s match with Richard and Lorraine from 88 to 115M could therefor be with one of Richard and Lorraine’s maternal grandparents or with either of the two paternal grandparents. This tells me that there is a bigger chance of the match being on the paternal side, but that the maternal side is not ruled out.

Updates on the Update

Since my update, I had a few important responses on the ISOGG Facebook Page that I would like to preserve in this Blog. Kathy Johnston, from whom I learned the visual mapping technique responded with a possible visual mapping:

I liked how she put in the Patricia and Joseph match suggesting that the purple could be the maternal side. I also received a response from M MacNeill who has been so helpful in working on the raw phasing of the Hartley and Butler families:

Here is a screenshot of comments relating to the image above:

Summary and Conclusions

• I could map out one further HIR, but I won’t at this point
• I had high hopes in mapping some paternal segments to specific grandparents on Chromosome 5, but it didn’t work out
• I did find an apparent Identical by Chance (IBC) or what I call a false match between Richard and Jeanette at Chromosome 5. It appeared to be real before I mapped it out.
• Future identified cousin matches may resolve the mapping of Chromosome 5
• I appreciate comments from readers that help me to re-think my conclusions