My First 1st Cousin DNA Results: Part 3 – The X Chromosome

In my first Blog about Cousin Rusty’s DNA matches, I discussed some maternal matches. I also looked at how first cousin DNA matches worked. In my second Blog about Rusty, I looked at the more complicated matching of nephew to aunt. In this Blog, I would like to look at the X Chromosome.

Here is how Rusty matches my family on the X Chromosome as shown in the Gedmatch Browser:

These are his matches with:

  1. Mom
  2. Sister Heidi
  3. Me (Joel)
  4. Sister Sharon
  5. Brother Jonathan

Here is an X Chromosome Map produced by M MacNeill before my brother Jonathan’s DNA results were in. He made this using our raw DNA results.

The blue is the maternal side where there are matches with Rusty. The red is what my sisters inherited on the Hartley side. MacNeill did not designate the blue by grandparent. The choices for maternal grandparents here are Alexander Rathfelder and Emma Lentz. Let’s try to figure out which is which.

Speaking of Emma and Alexander, here they are with their five children:

Rusty’s mom is the girl on the left and my mom is the girl on the right.

The X Path

The X Chromosome follows a particular path from our ancestors. The rule is that the X DNA never travels from male to male. So that means that two males in a path will break the X chain. Here are my top picks for X Chromosome matches:

The matches in the browser were through the green people up to Rathfelder and Lentz. Judy has the potential to match on the Lentz/Nicholson side. Joshua could also have shared X, though he is further down the ladder. Carolyn could match on the Nicholson side.

Carolyn’s Nicholson X DNA

I’ll look at Carolyn’s X DNA matches.

She matches:

  1. My Mom
  2. Sharon from 106672721 to 113198089 (7.056 cM)
  3. Jonathan from 139830607 to 143171128 (11.542 cM)
  4. Judith
  5. Joan

Based on Sharon’s small match, I would initially say that the darker blue is Lentz and the lighter is Rathfelder on the MacNeill Map. However, the problem with that theory is that I should match Carolyn also in that area. If I reduce the match level, I do have a match there with Carolyn:

Mapping Jonathan’s X

In order to be sure, we need to map Jonathan’s X. He has a larger X match with Carolyn than Sharon does – even though it looks smaller on the browser. Here is some previous X Mapping I had done for my sister Sharon (S), me Joel (J) and my sister Heidi (H).

It looks like I had already guessed that orange would be Lentz. Recall that Sharon’s (S) match with Carolyn was 106-113 and mine was 109-113 within the orange segments. When I compare Jon to his siblings, it looks like he has 3 crossovers:

As we are only looking at Jon’s maternal Chromosome, we are looking at the blue areas on the Chromosome Browser where he matches his siblings and the non-blue areas where he does not match his siblings.

This was pretty easy. I started on the right. Jon matches all his siblings, so that has to be green. Going from right to left, the segments alternate between green and orange. The only ambiguous part is on the left hand side where Heidi has a small orange Lentz segment. However, if I lower the thresholds for Jon’s match with Heidi, I get this left side match which clears up the ambiguity:

Gedmatch normally has a SNP cutoff at 500, but apparently they have not lowered that for the X One to One match and must still have a 700 SNP cutoff.

Now back to Jon’s match with Carolyn. I had noted above that it was at position 140 to 143. That just fits in to Jon’s Lentz mapped orange segment as shown by the red arrow below:

This confirms that yellow should indeed be assigned to Lentz. That means that green has to be Rathfelder – the only other maternal grandparent.

Now I’ll bring Rusty back into the picture with his matches to my family:

  • Rusty’s match with my mom is line 1
  • Heidi is line 2. You can see her Lentz indent on the left of her match with Rusty.
  • Joel is line 3. You can see the space left by Lentz in the middle of my large match with Rusty
  • Sharon is 4. Her match with Rusty stops at her Lentz (orange) segment
  • The newly mapped Jonathan is 5. He matches Rusty on his green Rathfelder segments.

So would we be able to guess Rusty’s X Map?

Rusty’s X Chromosome is either mostly or all Rathfelder. The part I’m unsure of is between 120 and 140 cM. The reason that I think that it might be Rathfelder is because Carolyn matches Judith and Joan in that segment and Rusty does not match any of those three by the X Chromosome. However, as Carolyn’s Nicholson matches go back at least another generation, that is not proof.

Looking at the ??????? Gap

I’m curious as to what is happening where Rusty and my mom don’t match. The answer to this goes back a generation. Alexander Rathfelder’s parents were Rathfelder and Gangnus. My mom and Rusty’s mom had two different X Chromosome maps showing how they got their X DNA from their grandparents. However, on their paternal side, their Rathfelder father gave them a full X Chromosome unchanged from his mother Maria Gangnus.

Here is Maria:

So due to the fact that Rusty’s mom and my mom both have the same paternal grandmother DNA on the entire length of their X Chromosome, that means that Rusty cannot have Rathfelder aka Gangnus DNA from 120 to 140. If he did, then he would have to show a match to my mother.

The result of our little thought experiment is that Rusty has to have Lentz DNA. Here is a possible scenario of what could have happened. This shows Rusty with his maternal grandparents. Then we see Rusty’s mom and my mom with their X Chromosome grandparents. Maria Gangnus is Alexander Rathfelder’s mother and Emma Lentz’s parents are George Jacob Lentz and Annie Nicholson.

What we know for sure is that Rusty’s mom and my mom both had a full X Chromosome from their paternal grandmother, Maria Gangnus. The only place for there to be difference is on my mom’s and Rusty’s mom’s maternal X Chromosome. Suppose that Rusty’s mom got her DNA from her maternal Nicholson grandmother and my mom got her DNA from her maternal Lentz grandfather. That would be why Rusty’s Lentz DNA would not match my Lentz DNA or my sibling’s Lentz DNA. We only got the X DNA that we received from our mothers and these mothers got DNA from different maternal grandparents in this location. We now know what Rusty’s X Chromosome map looks like. We don’t know what our mother’s maternal X DNA looks like. We only know they had DNA from different maternal grandparents from 120M to 140M.

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