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Old 10-11-2017, 06:43 PM
 
Location: Ozark Mountains
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Anyone know what is an "X-Match" at FTDNA?
I have several matches, they are 3rd or 4th cousins, but some are "x-match"
Does that means that they are related to me from my Mother's side?
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Old 10-11-2017, 06:47 PM
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Quote:
Originally Posted by ozarknation View Post
Anyone know what is an "X-Match" at FTDNA?
I have several matches, they are 3rd or 4th cousins, but some are "x-match"
Does that means that they are related to me from my Mother's side?
Yes if you are male.
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Old 10-12-2017, 08:09 AM
 
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What they call "x-matches" at FTDNA are usually noise, too small to be useful. So no, it does not mean they are related on your mother's side necessarily. If the segment on the X chromosome is over 20 cM then it is probably a valid X match. Unlike 23andMe, FTDNA requires autosomal matching (chromosomes 1-22) and will not show you people who match you only on the X even if it is a large segment.
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Old 10-12-2017, 10:13 AM
 
Location: Colorado (PA at heart)
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An X-match is someone who shares DNA with you on your X chromosome. The X chromosome is one of the sex chromosomes - females get two X chromosomes, one from their father, one from their mother. Males get one X chromosome from their mother, and a Y chromosome from their father. This is why women can't take the Y-DNA test, because they have no Y chromosome. So for men, sharing DNA on the X chromosome DOES mean your shared ancestors is on your mother's side. For women, it could be either side, but it does narrow down the possible branches. Because men only have X-DNA from their mother, it means the X-DNA can't pass through more than one generation of males in a row. I've attached charts showing where X-DNA comes from for males and females.

Due to the fact that there are fewer ancestors contributing to X-DNA, it means there is less recombination on the X chromosome. Because of this, you can share more DNA on the X chromosome with someone than you might expect for your relationship degree, and it can fool you into thinking you are a closer match than you are. This is why it's not wise to use X-DNA to estimate your relationship degree with someone, and why sharing ONLY X-DNA with someone (and no autosomal DNA) may mean your shared ancestor is too far back to identify.
Attached Thumbnails
X-Match help please-xdna-female.jpg   X-Match help please-xdna-male.jpg  
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Old 10-13-2017, 08:21 PM
 
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Originally Posted by PA2UK View Post
So for men, sharing DNA on the X chromosome DOES mean your shared ancestors is on your mother's side.
In theory, yes, but many male customers have reported false matches on the X chromosome when the segments are not long, matches they have that their mother does not. According to one blogger:

"While the generally accepted threshold for autosomal DNA is about 7cM, for X DNA, there appears to be a much higher incidence of false matches at higher levels than the rest of the chromosomes, as documented by Philip Gammon as in his Match-Maker-Breaker tool. This appears to have to do with SNP density."

In FTDNA, they count as an "X-match" anyone who shares 1 cM or more on the X. Really misleading.
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Old 10-14-2017, 05:46 PM
 
Location: Ozark Mountains
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Originally Posted by aries63 View Post

In FTDNA, they count as an "X-match" anyone who shares 1 cM or more on the X. Really misleading.
uhmmm not sure about that. I have my nephew at FTDNA, and he shares more than that with me, and he is an X-Match as well.
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Old 10-15-2017, 07:15 AM
 
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Originally Posted by ozarknation View Post
uhmmm not sure about that. I have my nephew at FTDNA, and he shares more than that with me, and he is an X-Match as well.
That's what I said: 1 cM OR MORE. So your nephew shares more.

In other words, they count as an X match people who have as little as 1 cM shared on the X. So a lot of those X matches are not valid because they are so small. The larger they are the more likely they are to be valid.
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Old 10-15-2017, 03:52 PM
 
Location: Colorado (PA at heart)
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Quote:
Originally Posted by aries63 View Post
In theory, yes, but many male customers have reported false matches on the X chromosome when the segments are not long, matches they have that their mother does not. According to one blogger:

"While the generally accepted threshold for autosomal DNA is about 7cM, for X DNA, there appears to be a much higher incidence of false matches at higher levels than the rest of the chromosomes, as documented by Philip Gammon as in his Match-Maker-Breaker tool. This appears to have to do with SNP density."

In FTDNA, they count as an "X-match" anyone who shares 1 cM or more on the X. Really misleading.
That doesn't mean the match is on their father's side though, it just means it's probably a false match/identical by state. Saying they're not necessarily a match on your mother's side is a little misleading because it would lead most people to believe it means they could be a match on their father's side, which for men, is not possible.
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Old 10-15-2017, 06:59 PM
 
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Quote:
Originally Posted by PA2UK View Post
That doesn't mean the match is on their father's side though, it just means it's probably a false match/identical by state. Saying they're not necessarily a match on your mother's side is a little misleading because it would lead most people to believe it means they could be a match on their father's side, which for men, is not possible.
I'm not sure what you mean by "they." Yes, a match labeled as an "X-match" (the person, not the segment on the X) can be related on the paternal side or maternal side, because it is the segment on the autosomes (chromosomes 1-22) that qualifies the person as a match in Family Finder which could be from either side. I am male and have a segment of 3 cM on the X shared with my paternal first cousin once removed. It is noise.
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Old 10-15-2017, 07:15 PM
 
Location: Colorado (PA at heart)
9,254 posts, read 14,286,242 times
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Quote:
Originally Posted by aries63 View Post
I'm not sure what you mean by "they."
The person you share DNA with on the X chromosome...

Quote:
Yes, a match labeled as an "X-match" (the person, not the segment on the X) can be related on the paternal side or maternal side, because it is the segment on the autosomes (chromosomes 1-22) that qualifies the person as a match in Family Finder which could be from either side. I am male and have a segment of 3 cM on the X shared with my paternal first cousin once removed. It is noise.
But that's not the point I was trying to make. Yes, the shared DNA on the autosomes can come from a different ancestor than the shared DNA on the X chromosome. But the shared X-DNA cannot come from a male's father. That was the point I was trying to make and I don't know why you're trying to pick it apart.
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