DNA Terms: X Match
Cheri Mello
<<Speaking of new dna terms, what is the X match now shown on family finder match pages?>>
This one is reeeeally hard to explain in an email. It's tough enough in person with a visual.
We have 23 pairs of chromosomes. The 23rd pair is the sex chromosomes. A man is XY (the Y makes him a man and we have a Y DNA test for that) and a woman is an XX.
The X match focuses on the X (or Xs if female) of this pair.
Let's start with a man, because he only has 1 X.
His Y: from his dad. This is not an X. Eliminate his dad and the entire pedigree beyond.
His X: From his mom (#3 in chart below). She gave one of her 2 Xs to him. Which one? Let's see, she got one X from her dad and 1 X from her mom.
Take that mom (#3 in chart below):
X from her dad (#6): The only way she could get and X from her dad would be if she inherited the X that was passed down by his mom (#13, as his Y came from his dad).
X from her mom (#7): She got either on of the Xs from her mom's parents (#14 & 15).
Keep following that pattern of inheritance.
If you have your genealogy program create a fan chart and you color in the people (Ahnentafel numbers are used here) you see this pattern. That way you don't have to figure out the pattern of inheritance, it's already been done for you:
To get these graphics, just google: x match chart
For a female, it's twice the fun:
Here's what I would do: Instead of dealing with the scientific laws of inheritance, I'd have my genealogy program print out a fan chart with names (you may have to tape them together). I'd take a highlighter and mark the names that correspond to my chart.
Because the way the X kinda recombines (or in the case of a man, it doesn't), the general rule is: The X match MUST be 10 cMs or greater on the X (23rd) chromosome AND you must be showing something in common on the other chromosomes.
My dad is half Portuguese (paternal), and half British Isles stuff (maternal). So his Y is Portuguese and his X is British. So I put his top 5 X matches into the Chromosome Browser at FTDNA:
Yes, I said 5 and you see 3 colors. The default display at FTDNA is 5 cMs. So I changed it to 10 cMs. Same thing. Where are those other people? So I changed it to 1 cM (WARNING!! DANGER!!! Will lead you to false interpretations!!!)
A-ha! 5 colors for 5 people! BUT....when you point your mouse at it, a pop up box appears that gives you more information.
ORANGE: 1st Cousin Nancy, half Welsh and half British stuff. You can see where her Welsh took the bites out of her British. That's a 53 cM chunk spanning the centromere and a 10 cM chunk at the end.
GREEN: Robert. I haven't figured him out yet. It's a 15 cM chunk and he matches on 2 other chromosomes with 9 and 14 cMs. One of those blocks has the same start positition as 1st cousin Nancy. He's probably a 5th cousin, so it would be best to wait this one out and find other 2nd-4th cousins to fill this in. Jumping from a 1st to a 5th or so cousin might be rather hard.
YELLOW: Karole. I haven't figured her out either. It's a 12 cM block. She matches one other chromosome, spanning the centromere as well. It'll be a distant cousin as well.
Now the 2 colors that didn't show up in the top chromosome:
PURPLE: Maggie. She's probably on one of my dad's Irish lines that is waaaaay back there. Her purple block is only 3.8 cMs and it straddles the centromere. Straddling the centromere is a problem, particularly if it's a small block. The centromere doesn't recombine. So it has some pretty old stuff in there. That could be some tiny Irish DNA fragment. Maggie shares only 1 other block with my dad.
BLUE: Julie. This is a problem. She's a Portuguese cousin 11 different ways (so far). The closest is a 5th cousin. Julie's mom was Portuguese. We don't know who Julie's dad was. My dad's X is British. This can't be Portuguese. That block is only 3.7 cM. Could that be some common Irish stock in both Julie and my dad? Yes. But trying to figure out which ancestor for a 3 cM block wouldn't be the best use of time. I wouldn't advise Julie to go chasing that block in trying to ascertain who her dad was. She needs to work with much, much larger blocks of DNA to build that part of her puzzle.
Now if you somewhat followed what I wrote, put it away and read it tomorrow. And maybe the next day. Then read one of the following blogs. And maybe another a few days later. If you read one thing on X match for a week, it would start to make a bit more sense.
DNA Explained by Roberta Estes: https://goo.gl/lrmf3a
The Legal Genealogist by Judy Russell: https://goo.gl/0NKUbZ
The Genetic Genealogist by Blaine Bettinger: https://goo.gl/3scssd
Listowner, Azores-Gen
Researching: São Miguel island: Vila Franca, Ponta Garca, Ribeira Quente, Ribeira das Tainhas, Achada
Rosemarie Capodicci
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Cheri Mello
Listowner, Azores-Gen
Researching: São Miguel island: Vila Franca, Ponta Garca, Ribeira Quente, Ribeira das Tainhas, Achada
cara...@aol.com
Cheri Mello
"E" Sharp
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