X dna help please

[andbro]

What doesit mean if I match someone for 79cm and 15cm longest block.

i just dont get x dna

Thanks

[MFWare]

If you are a man, then it means that your match is on your maternal side.

[andbro]

Sorry i should have said. I am a girl.

[Brunetmj]

As a woman you have 2 X's. One from your mother and one from your father. However your father got his X from his mother.
So you are a match either from your mothers side or from your fathers maternal side.

[JOlson]

If you are a man, then it means that your match is on your maternal side.

Not necessarily, when X=0. Any father-son generation in the path between you and your match will kill the X. Even if you are a woman. It can be in your maternal grandfather's, ggrandfather's, etc. generation, or your match's father, grandfather, or ggrandfather... The "X killing generation" can be on either your maternal or paternal side.

If, however, there IS a significant X value, then there is no father-son generation in the path between you and your match.

Here's a chart I made a while back that shows how X is inherited (and killed). Unfortunately, it only shows one side back to the common ancestor. Sorry it doesn't fit on one page.

http://www.gedmatch.com/x-inheritance2.gif

The other possibility for X=0 is that one of you didn't upload your X results :-)

[andbro]

head mash!!!!!!!!!!!!!!! Thanks

[JOlson]

head mash!!!!!!!!!!!!!!! Thanks

No kidding. I'm pretty sure that's why FTDNA still isn't doing anything with X. Bennett would spend all his time answering the questions. :-)

[Neves]

I like getting X matches because it is easier to find a common ancestors when you can automatically cross off 60% of them right off the bat. You can also find matches further back in time.

I prefer the chart in the first link which shows the ancestors you inherit x-dna from.

http://www.thegeneticgenealogist.com...-x-chromosome/

also...
http://www.yourgeneticgenealogist.co...a-testing.html

check out CeCe Moore's blogs, they are very informative

[limbicognito]

X-chromosome inheritance for 1st Cousin 1r

Could anyone help me to understand if it's possible for me to have significantly less x-chromosome in common with a maternal 1st cousin 1r than 20 or more 3-5th cousins?

I'm guessing it's either a mistake or I simply do not understand how x-chromosome inheritance works.

This is based on gedmatch results but the rules of x-chr inheritance should be the same regardless.

Thanks in advance/

[mkdexter]

This is completely normal to share just a little, or none in fact.

Is this maternal cousin connected via her mother or father to the same maternal grandparents? I'll assume since you said maternal that this is a connection via your mother to her parents and then back down the tree to this cousin.

[limbicognito]

Hi Matt,

Thanks for your reply.

Yes it's a maternal cousin. My mother's mother was his mother's sister. Or my maternal grandmother and his mother were sisters.

So it's perfectly normal for me to have almost no x-chromosome in common with him?

[mkdexter]

Yes they might share none at all.

I'll start with the grandparents. Xp = father's X to his daughter, X1 = mother's X from her father, and X2 = mother's X from her mother, to her daughter. Remember the daughters have XX so there are always a paternal and maternal X for them.

grandfather has
Xp

grandmother has
X1
X2

daughter 1 (your mother) has
Xp
Xm= X1 or X2 or X1+X2 mixed

daughter 2 has
Xp
Xm= X1 or X2 or X1+X2 mixed

So at that point your mother and your cousins mother's will share 100% of their X just because at miniumum they have the same father's X, (Xp).

After recombination again in the next generation everything can become jumbled. For one thing they would not have the same father so they won't share X on their paternal side, just their maternal side.

On their maternal only side,
the child of daughter 1 would have
Xm = (from grandparents) Xp or X1 or X2 or X1+X2 or Xp+X1 or XP+X2 or XP+X1+X2

the child of daughter 2 would have
Xm = (from grandparents) Xp or X1 or X2 or X1+X2 or Xp+X1 or XP+X2 or XP+X1+X2

As you can see, there are a lot of possible ways that child 1 (male or female) and child 2 (male or female) could have Xm (maternal) from the grandparents but not have the same X in the same location, thus compared to each other neither shares much with the other. Depending upon gendor they may not have a Xp or not but in any case it would not match between the two of them regardless.

If one's Xm = grandfather's xP and the other's grandfather's X1, then the cousins would not show up as sharing X (nothing matching) yet they would both have some X from their grandmother.

[mkdexter]

If one's Xm = grandfather's xP and the other's grandfather's X1, then the cousins would not show up as sharing X (nothing matching) yet they would both have some X from their grandmother.

I meant, If one's Xm = grandfather's xP and the other's grandmother's (not grandfather's) X1, ...

[limbicognito]

Thanks again mkdexter for the thorough explanation!

I guess I was just very surprised that 20 or more 3rd-4th cousins all share many times more X than I do.

Just to be clear my cousin is once removed, so he is the son of daughter 2 using your example:
Xp
Xm= X1 or X2 or X1+X2 mixed

daughter 1 (would be my grandmother)
Xp
Xm= X1 or X2 or X1+X2 mixed

Since he is male he would only have gotten his X chr from his mother (daughter 2), right?

So his X would share a lot with my grandmother (daughter 1), right?

My mother is the child of daughter 1
Xm = (from grandparents) Xp or X1 or X2 or X1+X2 or Xp+X1 or XP+X2 or XP+X1+X2

And since I am male I would only get the X chr from my mother.

So it would be a comparison of:

Xm= X1 or X2 or X1+X2 mixed
and
Xm = (from grandparents) Xp or X1 or X2 or X1+X2 or Xp+X1 or XP+X2 or XP+X1+X2

Still seems odd to me that I would have practically the lowest amount of X chr in common with my 1st cousin?

[mkdexter]

Oh.. didn't know for sure he was once removed cause you listed both scenarios.

Yes since you are both males that cuts off one side right away (X not XX) and leaves your maternal sides to rely on recombination moving segments to the same places in order to share.

When you look at the other comparisons to other people (the ones that seem higher) it is possible the defaults are too low, trying using 500 SNPs and 7cM.