The X Chromosome DNA in DNA Testing

All testing companies screen for X-DNA, however not all of them analyze the results. Sometimes it can be used to narrow the potential nature of a relationship between two autosomal DNA matches because of the distinctive inheritance pattern of X-DNA. Only a select group of specific ancestors can pass on X-DNA to future generations.

The X Chromosome Inheritance

A male has two sex chromosomes, the X and the Y. Unlike the 444444 autosomes (non-sex chromosomes), the X and Y don’t carry the same genes and aren’t considered homologous. Instead of an X and a Y, a human female has two X chromosomes. These X chromosomes do form a bona fide homologous pair. Because sex chromosomes don’t always come in homologous pairs, the genes they carry show unique, distinctive patterns of inheritance.

One reason the X chromosome is relatively intriguing is that it provides information about fewer probable relatives. At 7 generations, there are 128 autosomal predecessors, but only a small number of these (21 for men and 34 for females) are X chromosome ancestors, potentially simplifying analysis. X chromosome analysis involves more than merely calculating ancestry proportions as a whole. 

Using a test-taker and two cousins as an example First cousins (1C) are one of the cousins, and first cousins once removed are the other (1C1R). The X chromosome was passed down from their paternal grandmother to their fathers, who were brothers, and then onto each of the DNA testers represented in variously colored boxes in the graph. The paternal 1C1R underwent a second X chromosome recombination with his mother, and as a result, he inherited somewhat less of the same X-DNA than the paternal 1C.

Source: https://familylocket.com/x-dna-inheritance-and-recombination/

What Can You Do With X-DNA?

The majority of genealogical issues cannot be solved by X-DNA alone. It is used to support a notion in conjunction with other DNA data. A common ancestor idea, for instance, might be supported by atDNA, whereas the ancestral line that the common ancestor belongs to can be proven by X-DNA. By excluding other lines as potential candidates, X-DNA concentrates research on the ancestral lines that are most likely to have connected you to a particular person. The lack of an X-DNA match due to random recombination does not establish that you are connected on a specific line, but the presence of a large size match does suggest that you are related on an ancestral line through which X-DNA is passed down.  Many genealogists disregard X-DNA data due to the different inheritance patterns for X-DNA.

X-DNA Test Results 

An autosomal DNA test examines chromosomes 1 through 22 as well as the X chromosome. Raw DNA data makes up the X-DNA test results. Some online resources for DNA testing combine the raw autosomal data with the X-DNA data in the same file. Some, like Family Tree DNA, store the X-DNA information in a separate file. If the raw DNA data is in numerous files, make sure you download all of them to your own device. Remember that the policies might change over time, so you should always check the current standard to make sure you have all of your data.

Raw X-DNA data resemble raw atDNA data very closely, with the exception that the chromosome is given as X or 23 rather than 1 through 22. Family Tree DNA, 23andMe, and AncestryDNA all use X to denote the X chromosome; the other two use 23.

Using X-DNA Test Results

The fundamental procedures for using X-DNA are comparable to those for atDNA, but an X-DNA inheritance chart concentrates on the potential ancestral lines that contributed to a person’s X-DNA. Create a pedigree chart and list the details of your earliest known ancestors, for instance, all the way back to a great-grandparent or a more recent generation that has since passed away.  For each individual who has undergone an autosomal DNA test, make an X inheritance chart. Find a common ancestor on the ancestral lines identified on the X inheritance chart when the person matches both the autosomal and X-DNA. Examine any ancestry details that your DNA matches have revealed, and try to get in touch with your matches if you want further details.

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