This subject has suddenly become topical in the DNA email lists and I considered holding off until I learned more from the experts on the list, but I think the fact that I am completely at sea with this type of match has its relevance. It’s been six months since I received my test results and I still don’t know what to think about X Matches. I’ll explain where I’m at.
On FtDNA when I list my matches, there is a small dropdown panel at the bottom of each match in the list, showing further details. This panel provides many interactive options including listing ‘In Common With’, showing what other tests that kit has taken eg YDNA or MtDNA and giving their basic results. I can select the kit to compare in the chromosome browser. It shows the longest block on which I match this kit, and finally tells me if this kit is an X-Match or not.
I can also use the ‘Relations’ sort box at the top of the screen which by default is set on ‘Show All Matches’. If I change this to ‘X-Matches’ it will show me only my X-matches.
This is a potentially useful field. I have only potentially received DNA on my X-Chromosomes from just over half my matches so if I can confirm an X-Match, I can immediately eliminate nearly half my ancestors in determining the MRCA. In theory. In reality, it seems that X-Matches are highly prone to being IBS, and that large segments can come down basically unbroken from WAY back. I have not proved this either way yet, but I do have some potential connections on my non-X lines which show as X-Matches for small portions. Nothing concrete – hence my confusion.
Being female, I received an X chromosome from my mother and another from my father’s mother through my father. There is still a bit of confusion out there about this, with some pieces of writing stating that the X-chromosome only comes from the mother. They were probably written by men and therefore perfectly correct as far as they went. Men get only one – from their mother. Women get two – one from their mother, one from their father’s mother.
I have four children – three boys and a girl. My three boys only received their X-chromosome data from me. My daughter received one from me, one from my mother-in-law through her father.
I had two to pass on – one from my mother, one from my father. Which portions of my two that went to each child will be different. It is very doubtful that they received the same thing. One might have received more from my mother, one more from my paternal grandmother. So even though my three boys all received their X-chromosome from me, it won’t be identical.
We can see, given that coming from a female – male – female – male etc down that line, the X-chromosome does not recombine when coming from a male to his daughter. It might be a unique combination of his mother’s and his paternal grandmother’s, but once the man has it, he passes it on to his daughter’s in its entirety. It takes two to recombine. Hence the longevity. X-chromosome down that female – male – female – male – female line is going to take about 10-12 generations to turn into something unrecognisable, not 5-6 like Family Finder.
It makes it very hard to work with, but as I said earlier, potentially very useful. Not only can I eliminate almost half my ancestors in seeking this match, I can also use it to find deeper ancestors – if accompanied by a good paper trail. A good paper trail is so hard to achieve from maternal ancestors unless they were rich.
Adding to the usefulness – if they are an X-Match, the common ancestor is on one of their X-Lines as well. We can eliminate half of their tree also.
I created an X-Tree for myself in PAF. Just a simple tree with myself, my parents, my father’s mother, both my mother’s parents, my father’s mother’s parents, my mother’s mother’s parents – as far back as I could. Then I looked at my X-Matches to see if I could find a connection.
Of my four closest matches, the 2nd-4th cousin matches, unresponsive Jennifer is my only X-Match. Of the rest, four of my distant cousins on Prince Edward Island are X matches. This is way less than half of them and the segment is small, so I think they are probably IBS. However, until I deduce our exact connection, I have to keep them on the radar. Maybe I have more links than I knew with that place.
Annie McLeod, my known Scottish ancestor, is my mother’s father’s father’s mother so not an X-match.
Robert Lockley and Catherine Hingley are on my distant cousin Sarah’s X line, but they are not on mine so we are not an X match.
It may be that I happen to have inherited huge X-portions from an ancestor without many descendants and this is why I have so few, but a lot of people are dubious about using X matches to identify ancestry. I’ll keep studying it and maybe something will become clear.
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