Follow the “X”

By Don Taylor

Image by Caroline Davis2010 (CC BY 2.0)

Twenty-Two of our chromosomes are recombinant in nature, which means you receive 50% of your mother’s DNA and 50% of your father’s DNA.  The 23rd chromosome, the X-Y or X-X, is quite different. If you are a male, you received a “Y” chromosome from your father and you received an “X” chromosome from your mother. That X is a recombinant, in that it consists of 50% of your mother’s DNA. However, if you are a female, you received 50% from your mother as recombinant from her, but you also received your other X chromosome as a duplicate from your father. The effect of that is that the amount of DNA received from an ancestor through your X chromosome is higher if the ancestor path switches gender every generation. For example, my mother received 50% from her mother and 50% from her father. Her father received 100% of his X DNA from his mother (recombinant).

Blaine Bettinger (The Genetic Genealogist) has an excellent article, “More X-Chromosome Charts,” which provides charts showing both the Ahnentafel numbers and the percentage of X-DNA you received from which ancestors. The effect of this switching back and forth is that a male receives 12.5% of his mother’s father’s mother’s father’s mother’s father’s mother instead of the 0.78% that he received from that ancestor (a 5th great-grandmother) in the other 22 chromosomes.

I call that line a “zig-zag” line because it shifts gender every generation can provide insight into genetic connections that can really help in understanding matches and where you and that person may have a common ancestor.

The following are my “zig-zag” ancestors:

Ahnentafel #PersonSexExpected %
of X-DNA
3My motherF100
6Richard Earl Brown (1903-1990)M50
13Mary Elizabeth Manning (1878-1983)F50
26John William Manning (1846-1888)M25
53Minerva Ann Tolliver (1821-1902)F25
106Tulion Tolliver (unknown dates)M12.5
213Unknown 5th great-grandmotherF12.5

 In any generation you follow a woman’s mother, the expected % of X-DNA is cut in half. So my mother received 50% of her X-DNA from her mother. I have 50% of my X-DNA from my mother’s mother, so a similar “zig-zag” chart for my mother would be:

Ahnentafel #PersonSexExpected %
of X-DNA
3My motherF100
7Madonna Mae Montran (1893-1976)F50
14John Montran (c.1867-c.1897)M25
29Unknown 2nd great-grandmotherM25

Because my great-grandfather, John Montran’s life is such a mystery and because his parents are a complete mystery to me, discovering ancestors with whom I share X-DNA with may provide key insight into potential candidates for John.

If you share any of the above ancestors with me, I’d love to hear from you and try compare our matches in order to learn of our common ancestor. 

DNA Testing and Results Companies

23 and Me requires you to compare DNA in their browser and then manually determine if there is a match on the X-Chromosome. You can download your raw DNA data and import it into several other services. (Kits available for $69 until 23 Nov 2018)

AncestryDNA doesn’t provide information about X-DNA Matches nor does it provide for a chromosome browser. You can, however, download your raw DNA data and import it into FamilyTree DNA and GEDMatch. (Kits are available for $59 until 21 Nov 2018)

FamilyTree DNA shows you that an individual has an X-Match with you, even if that match is extremely low, even down to 1cM if they match otherwise at higher levels. You can test with FamilyTree DNA, with “Family Finder.” Alternately, you can also upload raw DNA results from Ancestry, 23andMe, MyHeritage and the National Genographic Project 2.0. (Kits are $79.00)

GEDMatch allows you to select whether a match is based on autosomal or X. By selecting X, you can see only those matches with whom you share X-DNA. If you look at the individual’s kit number and it begins with “A” they kit was imported from Ancestry. GEDMatch does no testing but allows you to upload your raw DNA data from various services including Ancestry, FTDNA, WeGene, MyHeritage and others. GEDMatch does no testing,

MyHeritageDNA does not show you your X-Matches (at least not with uploaded kit results).

LivingDNA does not show you any match data.

Looking solely at X-Chromosome match capability,  FamilyTree DNA and GEDMatch are the best, with 23 and Me following closely behind. AncestryDNA, Living DNA, and MyHeritageDNA do not support X-Chromosome match analysis. Look closely at your tree and your X-Chromosome, you may find that a new clue to help find that elusive ancestor.

————–  Disclaimer  ————–

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