Autosomal DNA tests for genetic genealogy

This is another post in a series on genetic genealogy. So far, I’ve written about the general topic, and the use of Y-DNA and mtDNA to trace back either a paternal or maternal line. These testing methods are great, and can take you back even tens of thousands of years in terms of very deep ancestral origins. However, neither one can tell you about closer-in family relationships, like your mother’s father’s brother’s children. This is where autosomal DNA tests for genetic genealogy can play a role.

As we’ve mentioned before, we humans have chromosomal DNA in the nuclei of all of our cells. The expression of this DNA defines who we are physically. As well, we have organelles in our cells called mitochondria, which also carries its own unique DNA, mtDNA, in the form of a loop. The mitochondria is the physical engine of cell metabolism. Back to the chromosomal DNA… in humans, this consists of 23 pairs of chromosomes. Of these, 22 pairs are autosomes, meaning that they have nothing to do with the sexual characteristics of the individual. One pair are allosomes, meaning that they do express the sexual characteristics of the individual. In women, there are two X-chromosomes. In males, there are one X-chromosome and one Y-chromosome.

So, genetic genealogy, as we’ve discussed it thus far either focuses on the male allosome for tracing a paternal line or the mitochondria for tracing the maternal line. There is a good deal more DNA available for testing; namely, the 22 pairs of autosomes.

As is common knowledge by now, we acquire half of these autosomes from our mothers and half from our fathers; and the same will be true for each of them. Since our mothers will have some of her DNA from her father, and he from his mother, and she from her father, and so on, our autosomal DNA is much more of a blend than is the case with either Y-DNA or mtDNA. Since our living cousins will have had a very similar blend of autosomal DNA transmission as we have received, the opportunity rises for using tests on autosomal DNA to prove up near-term family relationships that cannot be discovered with either Y-DNA or mtDNA testing.

For some time, autosomal DNA testing has been used commercially to provide the service of informing an individual of his or her geographic or racial origins. A standard test might report something like an individual being 1/8th Asian and the rest European, or 1/16th Native American, 1/8th African and the rest European, and so on. These tests are accomplished by checking for markers that are indicative these races.

Once more, in the interests of full disclosure, here are the results of my ancestral background from FamilyTreeDNA.

Personal ancestral background from autosomal testing

Since, if you’ve been reading my previous posts, you’ll recall that my more recent background is Scottish on one side and German-Russian on the other, provably back into the 1700s, this map might seem somewhat odd. However, at a deeper level, this map traces both of these genetic backgrounds to what is, at least currently, believed to be the geographic origins of those two sides, to Ice Age refuges of the peoples of Western and Central Europe, going back thousands of years. This sort of presentation is representative of the standard use of autosomal DNA testing, as I’ve said.

But, there’s a different approach to using the tests that, like other tests, involve matching against the results of other living persons, rather than hypotheses about ancient, racial origins. In the case of FamilyTreeDNA, this is called “Family Finder”. This quite amazing service can be used in a number of different ways, either as a stand-alone search tool, or together with Y-DNA or mtDNA to create mixed searches.

Here is a screen shot of one variant called the “Chromosome Browser.”

Chromosome Browser at FTDNA

You’ll see on the right diagrams of the 22 autosomes with color-coded regions that correspond to those areas in which my DNA has been tested to match the two individuals that I’ve selected on the left. On the lower left, I’ve configured the search to show me matches that have shown up since my last login. There are 6 already, and I used this service quite recently. This shows how quickly new participants are taking part in this service. I have picked out two folks with Germanic surnames. One of the names, Geiger, is known to me to have been in the same German-Russian enclave as my Wilhelm ancestors. To find a match with this surname is not surprising. By the way, to provide the other individuals whose names appear on the list, I’ve blurred out all but their surnames.

At the top left are the two individuals that I’ve selected and a setting to show regions that match at a 1 centimorgan level. This brings us to “what’s a centimorgan?” You can think of this as a span of positions along a chromosome that is likely to recombine in one generation at a 1% level or less. For we humans, this corresponds to about 1,000,000 base pairs. The information from the chromosome browser can also be viewed as a table. Here is an example:

Tabular detail for chromosome browser match

You can see that there are some extensive matches between myself and this person. In one span, of about 11 centimorgans, they and I match as many as 2,600 SNPs. Recall that a SNP is a single nucleotide polymorphism which represents the substitution of one nucleotide for another at some specified location on a DNA strand.

The Family Finder can also be used to present matches at various levels. In the following screen shot, I show a single individual whom I match as a “speculative relative”, someone with the surname, McLean. A relationship of 5th cousin is proposed.

Speculative match from Family Finder

In order to preserve this individual’s anonymity, I’ve blurred out some of the information that pops up. However, by clicking on their profile, I discover that one of their ancestral surnames is “Anhaus” from South Carolina. Interestingly enough, the Carolinas were a region to which many Scottish indentured servants were sent in the early years of the Americas. Anhaus is close enough to Angus to represent some possible match. This would be pure speculation without further investigation, but I guess that’s why the relationship is “speculative.” If I were interested in following up this speculation, I can check into the Anhaus family of South Carolina. In doing that, I find that the family likely came from Baden-Württemburg in Germany, which may mean the connection could be on my G-R rather than my Scottish side; or, who knows, some of both.

I personally believe that this Family Finder service at FTDNA is one of their most valuable features. It has only become available over the past year; but every time I log into my account, I find new and closer matches. By merging Y-DNA, mtDNA and autosomal DNA matching, this service brings together all of the possible test methods to prove up a relationship between two individuals, or family groups. If you had located some possible ancestor who might be on your family tree, and who had known living descendants, then establishing the relationship could be accomplished by testing your and their DNA using the FTDNA service.

Considering what I had mentioned earlier, about the low resolution of basic mtDNA testing, you may find it much more useful to focus on an autosomal test to prove a maternal relationship, or to augment an mtDNA match. For example, if you were investigating, say, whether some other individual and you shared a common maternal great-grandmother, you could do an mtDNA match; but even if you test both HVR1 & HVR2, there is still a large population of others whom you could match. On the other hand, this relationship of being second cousins would be demonstrated by large blocks of common autosomal DNA. So, proving or disproving such a relationship is really an easy matter.

While FTDNA doesn’t sequence your entire genome for their services, they do provide you with all of the data that they have obtained; and you can download that for your own records, should you desire. Beware of large files!

In summary, autosomal DNA testing represents a relatively new and increasingly valuable service. As I’ve mentioned before, I heartily recommend using Family Tree DNA as a test lab for exploring this area in your own researches.

Good luck!