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South King County Genealogy Society Blog

X, Y and Mitchondrial DNA

Posted: 07 Jun 2020 09:44 PM PDT

It's all about the chromosomes (and mitochondria)
The 23 chromosomes of a human male. Courtesy: National Human Genome Research Institute

X, Y and Mitochondrial DNA are less well-known and not used by many genealogical researchers. Both Y and MtDNA tests are more expensive than the more common autosomal DNA tests. 

X is always tested in an autosomal DNA test. However X results are less reported (FTDNA, 23andMe) or not reported at all (Ancestry, MyHeritage, LivingDNA), with the exception of Gedmatch.

Rather than covering generations of your ancestry, each of these DNA types cover a smaller portion of your tree, which some see as a weakness. However, because of that restriction, the researcher gets a focused result, which can be powerful, if the test will help you answer your research question. 

Y DNA tests were first offered to the consumer in 2000 by only one company: FamilyTreeDNA. Ancestry also offered Y and mitochondrial tests between 2012 and 2014  but not since then. There are other companies now offering Y DNA tests, but none have the genealogy focus of FTDNA. FamilyTreeDNA was also the first to offer mitochondrial DNA tests. Both Y and mtDNA tests are more comprehensive and less expensive than they once were. And FTDNA's autosomal product called FamilyFinder exposes X matches in their chromosome browser, as does 23andMe.

In 2007, 23andMe became the first company to offer autosomal testing, and have since the beginning done some limited testing of the X, Y and mitochondrial DNA, even predicting haplogroups for Y and mt DNA. A haplogroup is a broad grouping of patrilineal or matrilineal DNA which indicate a common origin. 

While one cannot search for X matches in 23andMe, X does show up in the chromosome browser if and only if there is a match on one of the 22 autosomes; the same is true for FTDNA. 

If you and a relative match only on X, that will not show up in FTDNA or 23andMe. However, autosomal test data from any company uploaded to Gedmatch will show X matches and allow X analysis. However, a match only on X could reach back far into the past because of the nature of X chromosome recombination.

X chromosome to the left, tiny Y to the right.
Courtesy: National Human Genome Research Institute
We all have an X chromosomeWomen have two! and men have one, which they get from their mother. Women have one from their mother, and one from their father's mother. If two men match on X, they both know that the match is on their mother's side of their family. It's a bit more nuanced for women.

If X DNA analysis will answer one of your research questions, urge your most likely matches to upload to Gedmatch. 

Men get their Y from their fathers, who got it from their fathersWhy spend all that money to do a Y DNA test? In my case, it focused on what my Dad wanted to know -- his research question -- which was to learn more about his father's Cowans, who came from Selkirkshire Scotland to Upper Canada (now Ontario) in 1832. Scots parish records before the mid-1700s are rare, so Y DNA offers some help, and it was then the only DNA tool available. 

One of my Dad's close matches had a very good tree back to Ireland, and we were able to surmise (but not yet prove) that both of our male lines came from a common ancestor in Stirling, Scotland around the time of the Plantation of Ireland in the early 1600s. 

Every human gets their mitochondrial DNA from their mother
Actual mitochondrial DNA is many time smaller than chromosomal DNA. By National Human Genome Research Institute - National Institutes of Health. National Human Genome Research Institute. “Talking Glossary of Genetic Terms.”Retrieved November 17, 2016, from, Public Domain,

I already had an autosomal test from 23andMe, so why would I want a mitochondrial test? Because my mother had died before I could test her. My dad had an autosomal test, so I knew that all the parts of my DNA that did not match him came from my mom. Mitochondrial DNA is special in that it follows the mother line and both men and women can test their maternal line. 

I wanted to test DNA that was my mother's alone -- along with her entire mother line. I've always been interested in the maternal line, particularly since I read The Seven Daughters of Eve: The Science That Reveals Our Genetic Ancestry by Bryan Sykes years ago, before consumer testing was available. 

So far, this mtDNA test has not led to any breakthroughs for me. Mitochondrial DNA is extremely stable, and even identical matches can be related through a common ancestor hundreds or even thousands of years in the past. That said, sometimes it is the only test which can support or disprove female parentage

We use DNA tests to answer our research questionsSo how does one use these tests? For all DNA tests, be prepared to do a lot of research on your matches' trees. Most of them do not know how to do the research, and you do. This is as true for your X, Y and mtDNA matches as it is for auDNA matches.

Make one of your trees your "home" tree for all of your DNA matches, and put everyone in one tree. "Build down" so that you can find descendants, and use the tools you have to make the matches and their line easy to find

If you have an auDNA test with Ancestry, I suggest using that as your main genetic tree, although you should always have a backup on your own computer and perhaps in the cloud as well. Place all your matches into that tree, no matter where the match's test is or what type. Tag the match and keep notes about the size of match, their haplogroup, where they tested; whatever you know right there in the tree. 

Not only does your tree enable you to find each of your matches, it is your best advertising to cousin/matches. So put trees everywhere, and refresh them sometimes. You may end up using other tools too, such as spreadsheets. I personally want to be able to see each of the people in a tree rather than just on a spreadsheet. 

If you have Legacy FamilyTree Seminars, I suggest the DNA Foundations series, which is 5 hours of video from Dr. Blaine Bettinger. This will give you an excellent background.

How to use X DNA to answer your research questionThe Foundations series mentioned above covers X briefly, but Which Spot Does X Mark, Anyway? X-DNA Testing in Action by Debra Renard goes into detail. Be sure to download and read the syllabus before watching. Besides that video, which is excellent, I suggest this article by Debbie Parker Wayne from NGS Magazine and:

Inheritance Fan Charts by Dr. Blaine Bettinger:

MS Word tables by Debbie Parker Wayne and Sue Griffith: 

Blogs & Wiki:

Y DNA: your paternal line
Y DNA is a huge subject. Basic to it is that there are two types of consumer test now. The most common test is STR (short tandem repeat) which shows up as a series of numbers which can be compared. More recent is the introduction of so called Big Y, which is an SNP (single nucleotide polymorphism) test, in a way akin to autosomal tests. I do not yet understand Big Y, but I won't give up! There is a series of links at which I plan to explore. Some links are dead, unfortunately.

The most important thing to do with Y DNA is join a project or two. Join one for your surname, or includes your surname. Those project admins are your best resource and best source of advice. There are also haplogroup project groups which can be helpful, and some for localities. Do an internet search and another search at FamilyTreeDNA.

You may also choose to upload to MitoYDNA, which is a new project replacing the now-shuttered Ysearch and Mitosearch public databases, which allowed people who tested with other companies to have a place to share their Y and mtDNA data. Read more about it at There is even a Chrome plugin to make the process almost automatic. 

Mitochondrial DNA: your maternal line
Debbie Parker Wayne has a short article from NGS Magazine here. Then dig in with Roberta Estes: and follow the entire series. Dr. Bettinger's Foundations in DNA series at Legacy also has an hour about mtDNA. 

Advertise!For both Y and Mt DNA, remember to add your haplogroup to your Gedmatch profile. Sometimes a match can be sorted just by comparing a haplogroup! There are other places where you can create a profile, and folks sometimes forget that cousins will search for them, just as we do. You will have a profile at each company you tested with, or have a tree on. Ensure it entices your cousins to get in touch! You can add a custom fact even to FamilySearch Family Tree with the haplogroup of the tested person, and their Gedmatch kit number.

If you use, did you realize that you can change your profile per group? For any genealogy group, list your Gedmatch kit number, haplogroups and where you have tested. 

Below is an image of my profile for our Genetic Genealogy/DNA group:

Join to automatically receive all group messages.