X DNA Comparisons on GedMatch

[familydar]

A bit like the infinite monkey theorem (see wikipedia), there's a good chance a number of unrelated people will have small chunks of their DNA arranged identically to others.  You don't necessarily share any ancestry with those individuals.  But the bigger the chunk, and the more of them (the numbers in the GEDmatch "total cM" and "largest CM" columns), the more likely it is that you could be looking at a genuine blood relative.

I think.

Jane :-)

[alfietcs]

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

A bit like the infinite monkey theorem (see wikipedia), there's a good chance a number of unrelated people will have small chunks of their DNA arranged identically to others.  You don't necessarily share any ancestry with those individuals.  But the bigger the chunk, and the more of them (the numbers in the GEDmatch "total cM" and "largest CM" columns), the more likely it is that you could be looking at a genuine blood relative.

I think.

Jane :-)

Richard and Jane....
That dull "thunk" sound, might just be that of a rusty penny dropping.
....It just might be, that's all i'm saying!.

I thank you both

[rsel]

I thank you

Your welcome

[Spike H]

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.

This should be the other way around. When a mother passes an X chromosome to her daughter it is a recombination of the X chromosomes she has received from each of her parents. It is the X chromosome that the daughter receives from her father that is an exact copy.
The "all or nothing" scenario relates to mitochondrial DNA (mtDNA).

[familydar]

Glad to be of help alfietcs, but please read what Spike H has to say about X chromosome inheritance - I got it wrong.

best wishes
Jane :-)