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geebee
02-11-2020, 08:08 PM
Knowing that an individual who shares DNA with you shares a segment with you on the X chromosome can be very helpful. This is especially true for males, since we only have a single X chromosome which can only have come from our mother.

23andMe, of course, does provide this information -- provided that your match is either sharing with you or has agree to display matching segments. MyHeritage also shows matching segments, but not on the X chromosome. Ancestry only reports the total amount of DNA shared, in centimorgans; and the number of segments.

Other companies, of course, may not provide even this much info. What I would like to see is for MyHeritage to report segment sharing on the X chromosome, and for Ancestry to do the same -- even if they continue not to provide a chromosome browser.

For me, just knowing I share with someone on the X chromosome is enough to tell me that I am likely related to them through my maternal grandfather's mother. This is because all of my X chromosome except for 20 cM surrounding the centromere came from my maternal grandfather.

There is a possibility also of the person being related to me through my maternal grandmother's mother, though only 20 cM of my X chromosome is from her. (I know that my maternal grandmother's father did not provide this DNA for a simple reason: my grandmother has maternal half sisters who have descendants who share DNA with me across this entire region.)

Osiris
02-11-2020, 09:41 PM
I identified my mother's biological father based on 2 3rd cousin X chromosome match at 23andme. If they were 4th chromosome matches instead I couldn't have done it because that forces you to review all siblings and branches. But by focusing on both x chromosome trees I was able to find the 1 couple that connected the two sides and recognize that they were my mother's paternal grandparents.

Pylsteen
02-11-2020, 10:21 PM
Especially X-matching at MyHeritage would help for me tracing it back further than my mother.

firemonkey
02-11-2020, 11:04 PM
I wish FTDNA wouldn't give x matches with less than 6cMs . Just 3/50 over 6cMs .

firemonkey
02-11-2020, 11:19 PM
With 23andMe I match a woman with an Irish/Scottish name who has Icelandic ancestors . Of the matches we share many are on the X and some also on chr 1-22 . The 1-22 chr are on 3,8,12 and 22. Size - 10.12-17.50 cMs . They're not large but better than those at FTDNA .

Pylsteen
02-12-2020, 07:05 PM
A funny line I discovered some time ago: my parents share a common ancestral couple from Antwerp during the early 1600s. On my mother's side they are one of my X-chrom candidates; on my father's side, they are X-chrom candidates of the 19th century ancestor I was named after.

Táltos
02-17-2020, 06:43 PM
The X Chromosome is actually going to play a big role for my daughter's Science Fair Project. :)

Osiris
02-25-2020, 06:36 PM
The X Chromosome is actually going to play a big role for my daughter's Science Fair Project. :)

Did she complete her project? What was the object of it?

Táltos
02-26-2020, 05:30 AM
Did she complete her project? What was the object of it?

Hi, not yet. It is due in May. The purpose: How will the X chromosome affect the amount of DNA a granddaughter can inherit from her grandparents?

geebee
02-26-2020, 02:05 PM
Should be fascinating. From what I've seen the amount can vary pretty widely -- even apart from considering which grandparent can't pass on any X-chromosome DNA to their grandchild.

My parents had an equal chance of passing on X-chromosome DNA to my sister's daughter, since my sister inherited an X chromosome from each of them. Yet my niece only matches my father on the first 11.06 cM. Obviously, that means that all the rest of my niece's maternal X chromosome came from my mother.

All of my only X chromosome is from my mother, of course. So I don't match my niece on this 11.06 cM. But I do match her everywhere else I match my sister. The only thing that excludes (besides the 11.06 cM) is 20 cM surrounding the centromere. 100% of my sister's maternal X chromosome is from our maternal grandfather -- and therefore from his mother.

So my niece ended up getting 11.06 cM from her maternal grandfather, and 170.78 cM from her maternal grandmother. That 170.78 cM, in fact, is from her maternal grandmother's maternal grandmother! My niece's son inherited 120.13 cM of this. That's a pretty big chunk of a chromosome to inherit from a 3rd great grandparent.

Saetro
03-01-2020, 01:38 AM
I would love the X-chromosome to help me with some mysteries.
But my X matches so far are not big enough to be unequivocal.
And that goes for most people I know - whom I recommend to leave such things alone as they can be a great time-waster and lead nowhere.

A few friends have large X matches and they are gold dust - invaluable.
May you be lucky enough to have one of those!

JFWinstone
03-05-2020, 08:47 PM
What kind of size would be considered significant on the x chromosome? My mother has an X Chromosome match to a South Korean on a broadly East Asian and Native American segment 18.1CM.

Geborgenheit
03-07-2020, 03:54 PM
FTDNA has promised that ethnicities will appear in their chromosome browser, hopefully on X chromosome(s) as well. I expect nothing else than Eastern European as on 23andme for me... Unfortunately, I don't have close matches on X chromosomes.

Osiris
03-07-2020, 10:31 PM
What kind of size would be considered significant on the x chromosome? My mother has an X Chromosome match to a South Korean on a broadly East Asian and Native American segment 18.1CM.

How's the rest of the segments? And X segment with no matching autosomal segments might mean it's a distant or sticky segment. The useful segment length for me was 50 cM for a 3rd cousin.

geebee
03-07-2020, 11:13 PM
How's the rest of the segments? And X segment with no matching autosomal segments might mean it's a distant or sticky segment. The useful segment length for me was 50 cM for a 3rd cousin.

In addition to having to pay attention to sticky segments, you also have to consider that some combinations of sexes give the X chromosome fewer opportunities to recombine. For example, the fewest opportunities for recombination occur when the DNA has been passed on through alternating males and females; the most opportunities would be through a series of all females.

I have more matching on the X chromosome with a 4th cousin once removed -- two segments, one of 24.49 cM and one of 33.54 cM -- than I do with a 2nd cousin once removed. With the latter I only share a single segment on the X chromosome, 31.45 cM in length. That particular segment has a lot of overlap with the segment I share with the 4th cousin once removed.

The key difference between these two cousins is that I share more overall with the 2nd cousin once removed (158 cM) than I do with the 4th cousin once removed. However, the 4th cousin once removed is also my 3rd cousin twice removed, but through his opposite parent. So we share 105 cM altogether.

Two things to remember about the X chromosome: (1) when passed from father to daughter, it's essentially without crossovers. So it's as if it's passed on from the father's mother directly to his daughter. And (2), even when the X chromosome can recombine, it doesn't necessarily do so. (Of course, this is also true for other chromosomes.) For example, I have a brother and sister who are identical on the X chromosome each inherited from our mother, and I am only different from these two a 20 cM region surrounding the centromere.

In my siblings' case, the entire chromosome is from our mother's father. In my case, two crossovers occurred. One was just before the centromere, and the other was just after. So both arms were from my grandfather, and the centromere region was from my grandmother.

What that means is that all three of us have the same matches on the X chromosome -- except at that 20 cM region, where my matches are on the opposite maternal grandparent's side. What's cool is that I also know which grandparent provided this region, thanks to the fact that my great grandmother was married twice. Since I match some descendants of my maternal grandmother's half sisters, I know this region came from my grandmother's mother.

Amerismed
03-10-2020, 11:45 AM
It's awesome how God created these unexplainable objects.