Understanding X DNA
This is a bare bones basic overview of X-DNA and why it is important. I solve alot of mysteries. My focus is on the immediate family of people who are adopted or they are missing one parent, usually a father. Going back to high school biology, women are XX and men are XY.
Edward's X-DNA Inheritance
Edward, an adoptee, can only inherit X-DNA from his mother. She inherited it from her mother and father but as we get to the men in this lineage, they can only inherit their X from their mother. The other half of Edward's 23rd chromosome is the Y-DNA that comes directly down the paternal lineage.
How Does This Help?
Using X DNA to narrow down Edward's birth family can be extremely helpful. If a male tester matches with another male tester on the 23rd chromosome, we know that that the connection between the 2 researchers are on the maternal line of their family trees.
In the example below, Edward, our adoptee, matches Jeff, another researcher, but at a very small amount. Because they match on the X DNA the match is on Jeff's maternal lineage as well as Edward's. Building out Jeff's pedigree tree and identifying where his X DNA could have come from will help us find common matches with one of these surnames.
Jeff
Shared DNA: 43 cM
Chromosome Browser from 23 and ME Test Results
This is still very important because Jeff shares several matches with Edward and we can safely assume that these are on his mother's side of the family tree.
When we look at the matches that Jeff and Edward have in common, we may find some closer matches that are not X DNA matches and that is ok. Unless there is a crossover between Edward's maternal and paternal lineage, we are still looking at his mother's side of the tree.
This chromosome browser example is from Edward's test results with 23 and ME. But to gain a broader number of maternal matches, we went to Edward's test results on ancestry.com and found that some of the matches that we have identified as maternal have also tested on ancestry.com. Ancestry has a larger database of testers and some of them share much more autosomal DNA with Edward making it easier to narrow down this lineage. As an added bonus, we found a half-sister to Edward using the gedmatch.com toolset.
Jane's X-DNA Inheritance
On our 23rd chromosome, or as I call it, our gender chromosome, women inherit X DNA from their mother and their father. Jane's mother inherits the X DNA from both her mother and her father. But Jane's father can only inherit X DNA from his maternal lineage.
I often look for X-DNA matches for women adoptees that are male. While "Jane" inherits X-DNA from both of her parents, her male match can only inherit his X DNA from his mother's lineage.
In this case, our adoptee, Jane, has a pair of half nephews. With the amount of DNA shared between Jane and John, it would appear that Jane and John could be either a 1st cousin or a half nephew, but a couple of additional clues help guide our research. John matches another male and these men are much closer in age to each other than they are to Jane. They are also half-brothers. What we do know for sure is that the match runs up through John and his half-brother's mother's lineage. We do not know yet if this is on Jane's maternal or paternal lineage.
John
Shared DNA: 839 cM
Additional research has found that John's maternal grandfather was also adopted, and shared common ancestor is Jane's paternal grandmother which is John's great grandmother. Jane's paternal grandfather is still a mystery.
X-DNA is a very important tool in the search angel's toolbox and I highly recommend that adoptees test in multiple test locations starting with ancestry and 23andME.
