Phasing question - GEDmatch (find, percentage, blood, grandmother)

[westsideboy]

I'm a guy. I got a Y from my dad, an X from my mom.

All three of us have taken DNA tests through Ancestry.com. All the files have been uploaded to GEDmatch. I also have a file from my maternal grandmother. I used my mother and grandmother's file to create a "phased" file to represent my maternal grandfather's contribution to my DNA. As far as autosomes go, this seems to have worked. My grandmother and I share the same cM length as I do with the phased maternal file that is supposed to represent her contribution to my genome.

Here is the question:

I match my mom AND my maternal grandmother along the entire length of my X chromosome. All 196.1cMs of it. I match the phased file representing my grandmother along all 196.1cMs. Yet, I don't match the phased file that is supposed to be my grandfather's contribution to my X chrome at all, zilch, nada.

Is this biologically possible? It would mean (as I understand it) that my mother's two X chromes did not recombine, and one of them (the X my mom got from my grandmother) passed down to me in its entirety.

I am thinking this is a shortcoming of the phasing app, but any guidance or information would be much appreciated on the biology here.

[suzy_q2010]

Originally Posted by westsideboy

I'm a guy. I got a Y from my dad, an X from my mom.

All three of us have taken DNA tests through Ancestry.com. All the files have been uploaded to GEDmatch. I also have a file from my maternal grandmother. I used my mother and grandmother's file to create a "phased" file to represent my maternal grandfather's contribution to my DNA. As far as autosomes go, this seems to have worked. My grandmother and I share the same cM length as I do with the phased maternal file that is supposed to represent her contribution to my genome.

Here is the question:

I match my mom AND my maternal grandmother along the entire length of my X chromosome. All 196.1cMs of it. I match the phased file representing my grandmother along all 196.1cMs. Yet, I don't match the phased file that is supposed to be my grandfather's contribution to my X chrome at all, zilch, nada.

Is this biologically possible? It would mean (as I understand it) that my mother's two X chromes did not recombine, and one of them (the X my mom got from my grandmother) passed down to me in its entirety.

I am thinking this is a shortcoming of the phasing app, but any guidance or information would be much appreciated on the biology here.

Yes, recombination of the X chromosome is funky, and inheritance such as you have is not unusual at all.

https://dna-explained.com/2014/01/23...osome-that-is/

"Robert Paine, a long-time genetic genealogy contributor and project administrator reported that in his family medical/history project, at 23andMe, 25% of his participants show no recombination on the X chromosome. That’s a staggering percentage. His project consists of 21 people in with 2 blood lines tested 5 generations deep and 2 bloodlines tested at 4 generations

One woman’s X matches her great-great-grandmother’s X exactly. That’s 4 separate inheritance events in a row where the X was not recombined at all."

[westsideboy]

Originally Posted by suzy_q2010

Yes, recombination of the X chromosome is funky, and inheritance such as you have is not unusual at all.

https://dna-explained.com/2014/01/23...osome-that-is/

"Robert Paine, a long-time genetic genealogy contributor and project administrator reported that in his family medical/history project, at 23andMe, 25% of his participants show no recombination on the X chromosome. That’s a staggering percentage. His project consists of 21 people in with 2 blood lines tested 5 generations deep and 2 bloodlines tested at 4 generations

One woman’s X matches her great-great-grandmother’s X exactly. That’s 4 separate inheritance events in a row where the X was not recombined at all."

Thanks. That is probably the answer then. I just need more spit from relatives to confirm.

[suzy_q2010]

You're welcome!

Would you keep us updated on what you find?

[westsideboy]

Originally Posted by suzy_q2010

You're welcome!

Would you keep us updated on what you find?

Absolutely. I have a pending kit for my maternal great-uncle (grandfather's brother.) So, I "should" be a strong X-match to him. If not, it would support the theory that I got my grandmother's X in its entirely.

[westsideboy]

Update:

My maternal great-uncle's (grandfather's brother) kit is in. As expected, he and my mother are a partial match on the X chromosome.

I do not match my great-uncle at all on our X. My X matches one of my maternal grandmother's exactly.