There seems to be a lot of confusion about the different “kinds” of DNA and how they can be used for genetic genealogy.
It used to be simple. When this “industry” first started, just a dozen years ago, you could test two kinds of DNA and it was straightforward. Now we’ve added more DNA, more tools and more testing companies and it’s not quite so straightforward anymore.
Here’s a basics primer.
1. Y-line DNA – tests the Y chromosome which is passed from father to son, along, in most cases, with the surname. Only men can test for this, because only men have a Y chromosome, leaving female genealogists with Y chromosome envy, having to go and beg off of their fathers, brothers, uncles and male cousins to test for the surnames in question. We compare the results of the Y chromosome test between males to see if they match and are related in a genealogical timeframe. We also obtain the haplogroup which defines deep ancestry, such as European, African, Asian or Native American. Surname, haplogroup and other interest projects (such as Acadian, Melungeon, Cumberland Gap, etc.) exist for both Y-line and mitochondrial DNA at Family Tree DNA. These projects are indispensable for both genealogy and genetic genealogy research.
2. Mitochondrial DNA – is passed from mothers to both genders of her children, but only passed on by females. Males carry their mother’s mitochondrial DNA (mtDNA) but they don’t pass it on. We compare mutations to see of people share an ancestor in a genealogical timeframe, but because the surname changes in every generation, it’s more difficult genealogically to make the connections. The lack of a central data base prevents people from being able to determine if others from the same genetic line have already tested. For Y-line, surname projects and surname matches provide this function. Mitochondrial DNA testing also provides a haplogroup which defines deep ancestry, such as European, African, Asian or Native American. Family Tree DNA is the only commercial company to offer full sequence testing which is sometimes necessary to determine whether a match is really genealogically relevant. When testing the HVR1 or HVR1 and HVR2 regions only, meaning the participant did not purchase the full sequence test, Family Tree DNA doesn’t just “estimate” haplogroups, but runs a panel of 22 SNPs to accurately assign a haplogroup for the participant.
The paths of inheritance for both the Y-line, blue, and the mitochondrial DNA, red, are shown below. If you’d like more specific information about how this works, with some examples, you can download the paper, DNA Testing for Genealogy – the Basics, from my website, www.dnaexplain.com under the Publications tab.
3. Autosomal DNA – tests the rest of the DNA provided by both parents on the 23 chromosomes, not just two direct lines, as with Y-line and mitochondrial DNA. Older tests of this type tested between 21 and about 300 markers, but current generation testing provided by Family Tree DNA (Family Finder test), 23andMe and AncestryDNA test use about 700,000 locations and are in an entirely different category in terms of their usefulness and accuracy to genealogists. These tests provide a list of cousins from all of your lines, but it’s up to you to figure out how these cousins are related to you. The testing companies provide different tools to help in this quest. Both Family Tree DNA and 23andMe provide the ability to download your raw data results so that you can do further analysis personally and by using several online tools, the most popular being GedMatch. AncestryDNA, the autosomal test through Ancestry.com, does NOT provide this capability and is deficient in other matching tools, providing no chromosome mapping or comparison capabilities, leaving customers significantly in the dark as compared to the tools at Family Tree DNA and 23andMe. Autosomal tests also provide an estimate of percentages of ethnicity. 23andMe only uses 3 population groups, European, African and Asian, while Family Tree DNA uses significantly more. Ancestry reports erroneously high Scandinavian numbers for many people with no Scandinavian ancestry, so be somewhat leery of their ethnicity projections.
The inheritance paths for autosomal DNA are shown below. You can see that this includes all of the various ancestral lines, including the lines that contribute the Y-line and mitochondrial, but those are separate and different tests providing different kinds of information.
4. The X Chromosome – has special inheritance properties that allow people to use these results separately from the rest of the autosomal results, although the X chromosome is a part of the 23 sets of chromosomes used for autosomal testing. The inheritance paths are different for males and females, because males only inherit an X chromosome from their mother (and a Y from their father which makes them male), but women inherit an X from both of their parents. I show these charts and discuss how to use the X Chromosome for genealogy, giving two examples, in my blog posting, X Marks the Spot. At this point, both Family Tree DNA and 23andMe include X raw data in their downloads. Only 23andMe shows matches specifically on the X chromosome although Family Tree DNA is planning to release this functionality. Ancestry does not include any X matching or data, so you cannot use the X chromosome information in any way if you have tested at Ancestry. The best way to functionally use the X information is to diagram your family lines that contributed to your X chromosome using your pedigree chart and Blaine Bettinger’s charts, found in my blog (and his previously) and upload your results to http://www.GedMatch.com. GedMatch provides X chromosomal matching utilities along with lots of other DNA analysis and comparison tools. GedMatch is free, but donations are encouraged and appreciated.