X DNA Comparisons on GedMatch

[alfietcs]

Hi

I am putting my hand up here, and admitting to the fact that I am really struggling with GedMatch and understanding what much of it actually means, like centimorgans, and chromosomes, and which ones, one is supposed to be looking for etc etc. But I accept that it is something I will hopefully learn over time.

However, what I really don't understand is the X matches. I have a long list of 2000 names with X matches, but for most of them, when I click to compare, we seem to share no dna at all.
So why are they showing as matches?
I get that they could be useful for showing if we might have a link on our female lines, but I don't get why they are there if there is no genetic link.

Am I being really dense?

Many thanks in advance

[rsel]

Hi,
   I am no expert on this myself, and like you have struggled to get my head around the GedMatch site (so much of it assumes you know an awful lot about the subject :-) ).
   However, where are you looking when you say you click compare and that you seem to share no DNA at all ? are you talking on the Chromosome browser or the list of results from the one-to-many options ?   If you are on the browser, then the X matches will be listed under Chromosome 23, if you are looking at the list of results from the one-to-many, then you may not see anything in the 'Autosomal' column as that is just chromosomes 1-22 (is my understanding)

Richard

[Kimbrey]

I wonder if there is something here to help?

https://isogg.org/wiki/X-chromosome_testing#X-chromosome_inheritance

[familydar]

Just to add my two-penn'orth, this is what I see when I do a one to many on GEDmatch.  If alfietcs is talking about the columns headed "X-DNA" I think these relate to whether there is a match on the X chromosome.  Men have one, women two (and no Y).  I've deduced this because what you are looking at in my attachment is my DNA and the top two matches are my parents. 

If I sort on the X-DNA Total cM column there are numerous low level (<20cM) "hits" with both males and females, I'm guessing many (all?) of these are just coincidence.  I don't know if the X chromosome can be partially inherited in the way that chr 1-22 can. 

I have no X chromosome commonality with a verified match through my mother's paternal line.  Neither do I share any X-DNA with other cousins on my father's line, whether maternal or paternal.

See later post (reply 13) from Spike H regarding this next paragraph:

As women have two X chromosomes, if X-DNA inheritance is on an "all or nothing" basis, then daughters presumably have a full match (or as near as) on one of the pair with their mother.  I think (if I'm wrong please get in touch and I'll retract this) sons do also, but might not get the same X chromosome as their siblings (50% chance I suppose).  Sons get their Y chromosome from their father (their mother doesn't have one), which is why the Y chromosome is used for paternity testing.

Other than for parent/child relationships, a "hit" on the X chromosome doesn't necessarily mean there will also be matches on autosomal chromosomes 1 - 22, and vice versa.

Jane :-)

[Kimbrey]

A few months ago I joined my own and my brothers kits to a Project being run by a Gedmatch member -he is looking at the amount of X Chromosome inherited by siblings with the same parents

Kim

[alfietcs]

Hi,
   I am no expert on this myself, and like you have struggled to get my head around the GedMatch site (so much of it assumes you know an awful lot about the subject :-) ).
   However, where are you looking when you say you click compare and that you seem to share no DNA at all ? are you talking on the Chromosome browser or the list of results from the one-to-many options ?   If you are on the browser, then the X matches will be listed under Chromosome 23, if you are looking at the list of results from the one-to-many, then you may not see anything in the 'Autosomal' column as that is just chromosomes 1-22 (is my understanding)

Richard

Hi Richard.
I am looking at the "one to many matches" page. On the left side columns of the table you can see your autosomal matches and on the right, there is a column which shows if you have an X match. Many are blank but some are X matches. Familydar has very kindly posted a screenshot.

I have also run the "one to many" scan looking for x matches only.
I suppose what I don't understand is why some have a chromosome match and some don't.
And I don't understand why the one's that don't are listed at all. I'm just very confused:) .

I'm really sorry if I'm not explaining myself very well.

[alfietcs]

I wonder if there is something here to help?

https://isogg.org/wiki/X-chromosome_testing#X-chromosome_inheritance

Thank you for posting this.
Admittedly, I clicked on the link, and read one of the articles, and it made my head hurt:).
Maybe Im not wired the right way to understand it.

I will try again though, so many thanks.

[alfietcs]

Just to add my two-penn'orth, this is what I see when I do a one to many on GEDmatch.  If alfietcs is talking about the columns headed "X-DNA" I think these relate to whether there is a match on the X chromosome.  Men have one, women two (and no Y).  I've deduced this because what you are looking at in my attachment is my DNA and the top two matches are my parents. 

If I sort on the X-DNA Total cM column there are numerous low level (<20cM) "hits" with both males and females, I'm guessing many (all?) of these are just coincidence.  I don't know if the X chromosome can be partially inherited in the way that chr 1-22 can. 

I have no X chromosome commonality with a verified match through my mother's paternal line.  Neither do I share any X-DNA with other cousins on my father's line, whether maternal or paternal.

As women have two X chromosomes, if X-DNA inheritance is on an "all or nothing" basis, then daughters presumably have a full match (or as near as) on one of the pair with their mother.  I think (if I'm wrong please get in touch and I'll retract this) sons might also, but stand a 50% chance of getting their (single) x chromosome from their father.  They certainly get their Y chromosome from their father, which is why the Y chromosome is used for paternity testing.

Other than for parent/child relationships, a "hit" on the X chromosome doesn't necessarily mean there will also be matches on autosomal chromosomes 1 - 22, and vice versa.

Jane :-)

Hi Jane

Thanks alot for your reply and for attaching the screenshot.
Yes, it was the X matches listed that were really confusing me.

What I don't really understand is why some are there at all.
There were matches on my "one to many" X chromosome search, that don't appear on my "one to many " autosomal search. If we share no DNA then why are they there at all?

I am really sorry if i'm not getting it. I feel a bit silly to be honest.

Maybe I should stick to paper and census forms:)

[rsel]

What I don't really understand is why some are there at all.
There were matches on my "one to many" X chromosome search, that don't appear on my "one to many " autosomal search. If we share no DNA then why are they there at all?

Ok, lets see if I am understanding you correctly here.....You have done a one-to-many match on the X chromosome, and see some matches there, that don't appear when you do a one-to-many on the Autosomal. Is that correct ?
if so then that is perfectly normal, as I understand it. I think you may have mistakenly believed that the Autosomal compare, is looking at your whole DNA, which its not. The Autosomal check is looking at chromosomes 1 thru 22 for the comparison, but the results list also mentions if there is a match on 'X' (or chromosome 23). On the one-to-many match on the X chromosome, match it only looks at the X chromosome (23), so you may have some people that only match on that single chromosome and not any of the other 22, hence why they only appear on that list.  The net result is that they are all DNA matches for you, that share DNA just in different chromosomes :-)

Richard