20 February 2016

atDNA Testing: Who can Test and How can it Help your Genealogy?

 by Emily Aulicino

Anyone can test their autosomal DNA (atDNA) and match both males and females. Autosomal DNA determines your traits. It is the reason we look like our parents and siblings, but not exactly alike, except for identical twins. Even in the case of identical twins, there are differences that can be detected with detailed DNA testing.

Autosomal DNA does not provide information on just the all-male or all-female lines. This is what Y-DNA (for males) and mitochondrial DNA (mtDNA) (for females and males) testing does. Instead, autosomal DNA tests all the chromosomes except the Y chromo­some, which only males have. Autosomal testing does include the X chromosome. Because inheritance of the X chromosome varies with gender, details on the X chromosome and how it is inherited will be covered in a future lesson, or see Dr. Blaine Bettinger’s post: http:// www.thegeneticgenealogist.com/2009/01/12/more-x-chromosome-charts/.

Autosomal DNA is received randomly from each parent during meiosis. The randomness varies with each child who is conceived. Children get approximately 50 percent of their DNA from each parent. For this reason, autosomal tests will not usually give matches further back than six generations with any mathematical cer­tainty. However, there are circumstances that can allow matches to older generations. To understand this more clearly, consider that your fourth great-grandparents (sixth generation) gave 50 percent of their DNA to their child. That child (your third great-grandparent), in turn gave 50 percent of their DNA. However, that would only be about 25 percent from that fourth great-grand­parent. Therefore, the next generation (your second great-grandparent) would receive about 12.5 percent of the DNA of that fourth great-grandparent. As you can see, in a few generations, the DNA from a specific fifth or sixth great-grandparent would be negligible, in most cases.

Approximate percentage of DNA inherited from parents and grandparents:

Mother, father
Grandfathers, grandmothers
2nd Great-grandparents
3rd Great-grandparents
4th Great-grandparents
5th Great-grandparents
6th Great-grandparents
7th Great-grandparents
8th Great-grandparents
9th Great-grandparents

However, if you descend from a population group that is endogamous (featuring intermarriage within a group according to custom or law such as some religious groups or some families in Colonial America), you can inherit more DNA from particular ancestors. In this situation, matches you receive can go back farther than six generations, with the testing company suggesting that the relationship of the matches is closer than they really are. Each ancestral marriage between cousins of any degree or otherwise blood-related persons increases the share of DNA they pass down from their common ancestors. The closer their relationship, the greater the effect can be. For example, one set of my paternal grand­parents were first cousins. I received a match stating a woman and I were third cousins. I already knew my connection with this woman as we had discovered our genealogical connection before DNA was ever used. She and I are really seventh cousins!

Because the atDNA from both parents mixes ran­domly at meiosis, each child typically receives different segments from each parent, so some siblings may car­ry a certain trait while other siblings do not carry that same trait. In basic biology class, we learned that some traits are recessive while others are dominant. In the diagram below, you can see a hypothetical family with four children and what they inherited based upon the DNA mixes.

Both parents have brown hair, but both have the recessive red hair gene, one parent represented in the top row, the other in the first column. The odds are they could have one child with red hair (rr), and two other children who inherited the recessive gene (Br, rB) and who could pass it along. If one of the above children who either has red hair (rr) or also carries the red hair recessive gene (Br, rB) marries a red-head or someone else with the red hair recessive gene, then there could be more red-heads in the family.

                        Father on the top line; mother on the left column

Text Box: MotherBrown

The companies that currently offer autosomal testing are Family Tree DNA, 23andMe, AncestryDNA, and Geno 2.0. These companies vary in some respects. Everyone but Geno 2.0 tests around 700,000 SNPs. (SNP, pronounced snip, is an acronym for single nucleotide polymorphism. In simplest terms, it is a location where the DNA changes in the general population.) Geno 2.0 is unique and deals with ancient ancestry. That company is covered separately (see companion story on page 32).

Two of the companies, FTDNA and 23andMe, offer some type of chromosome chart where you can specifi­cally see where you and your match share the same DNA. FTDNA’s Family Finder and 23andMe’s Relative Finder allow you to download the raw data files so you can re­view them in Excel or a similar spreadsheet program. AncestryDNA does not provide a chromosome chart, but you can download your raw data and view it in a third-party tool called GEDmatch. Only Family Finder allows you to see the name of the match and the per­son’s email. The other companies allow you to contact the match only through their website. As of this writing, FTDNA is allowing 23andMe(V3) and AncestryDNA users to transfer their raw data to the FTDNA database for free. https://www.familytreedna.com/Autosomal­Transfer

Y-DNA deals only with the all-male or top line of a ge­nealogy pedigree chart (hence the surname line in most cultures), and mtDNA deals only with the all-female or bot­tom line of the pedigree chart. The atDNA gives you matches on these and the other lines of your pedigree chart, without restriction by gender, going back with some surety for about six generations from the tester. For this reason, it is wise to test as many older generations of your family as you can, as well as siblings.

Like any other DNA test, autosomal DNA tests give you matches, but it is up to you and your match to discover where on your pedigree chart your common ancestor lies. If the connection is not identified through your paper trails, atDNA information can provide an alter­native. This process involves the analysis of the data in a chart or spreadsheet. There are ways to narrow this hunt, and the basic premise is to test first to third cousins. For example, I tested my paternal first cousin Doug. If he and I match a person (I will call Mary) on the same chromosome at the same segment, then I know Mary matches on my father’s line. The next step is to deter­mine if Mary is on my father’s paternal or maternal side. To accomplish this, I tested my paternal grandmother’s nephew Dan (my first cousin, once removed). If Dan, Mary, and I match, then I know the common ances­tor is on my paternal grandmother’s line. By testing parents and child and/or several cousins, one can map one’s chromosomes and actually determine from what ancestor you received what sections or segments of your DNA. More information on chromosome mapping for those who wish to test various family members will be covered in a future Bulletin column, or get a copy of my book, Genetic Genealogy: The Basics and Beyond.

Autosomal testing is also good for adoptees who would like to contact close relatives in order to gath­er more information on their family. It is important to remember that everyone you match is related to you, however distantly.

In summation, autosomal DNA provides the tester a list of cousins with whom the tester shares a common ancestor anywhere on their six-generation pedigree chart and sometimes even farther back, as when cousins have married cousins. Mapping the chromosomes is the best way to determine the common ancestor for your matches and can be accomplished more easily by testing cousins where possible. Remember to choose the company that best fits your needs, and if possible test with all three companies to be in each of their databases in order to find more cousins.

The Genographic Project, an arm of the National Geographic Society, launched their Geno 2.0 test in the fall of 2012. This test, like Geno 1.0, is a scientific study to research the migration patterns of our ancient ancestors, but is designed to have a larger impact on population genetics informa­tion, as well as the genetic genealogy world.

Geno 2.0 does the following:
·   Tests your most ancient ancestry, so this may not be the first test you wish to do for genealogy.
·   Reports the two population groups to which the Genographic Project believes you are most related out of a total of 43 populations
·   Replaces the deep subclade (a subgroup of a haplogroup) test at FTDNA for Y-DNA, generally providing your most accurately known terminal SNP thus determining your subclade
·   Reports the percentage of your autosomal DNA that is (allegedly) originally from Neanderthal and Denisovan hominids

Geno 2.0 uses 130,000 autosomal and X-chromosomal SNPs including 30,000 SNPs from regions of interbreed­ing between extinct hominids and modern humans.

Recently, DNA evidence has shown that modern humans inbred with the Neanderthals who populated Western Eurasia. Neanderthal DNA is 99.7 percent identical to humans, and scientists believe that many humans may have inherited one to four percent of their DNA from Neanderthals. Scientists also believe some Neanderthals and some modern humans inbred with the Denisovans who populated Eastern Eurasia. It is thought that islanders in Papua New Guinea may be distant cousins of the Denisovans. With the 2008 discovery in Siberia’s Denisova cave of a 40,000 year-old finger bone of a young girl referred to as X-Woman, and a tooth of a Denisovan adult, the entire Denisovan genome has been extracted.

Besides the X-DNA and autosomal DNA, the Geno 2.0 test uses an extensive number of SNP mark­ers from mtDNA and Y-DNA that will improve the scientific knowledge of the geographic origins of our ancient ancestry by delineating between populations and narrowing the geographic areas where our ancient ancestors were located. This means breaking down a European haplogroup into smaller locations, a wonder­ful advantage for studying your ancient ancestry and its migration.

Geno 2.0 uses the new Phylogenetic Tree from Dr. Doron Behar’s paper, A Uniquely Anthropological Approach to Human Origins and Dispersals. Dr. Behar and his col­leagues have revolutionized the mtDNA Phylogenetic tree so that instead of comparing your mtDNA to the rCRS (Revised Cambridge Reference Sequence), the new RSRS (Reconstructed Sapiens Reference Sequence) will be implemented. The RSRS is a proposed system com­paring mitochondrial markers that include the known Neanderthal sequences. This system gives a more ac­curate view because haplogroups closer to our ancient origins will have fewer mutations than those haplogroups that are more recent, thus displaying the haplogroups in a better time-oriented sequence. In the past, the rCRS showed fewer mutations for Haplogroup H (the CRS contributor’s haplogroup) with many for haplogroups that are more ancient and closer to Mitochondrial Eve, the oldest-known female haplogroup, thus displaying mutations in a sometimes backward manner.

About 15,000 SNPs with both new SNPs and SNPs from the established Y-DNA Phylogenetic Tree are included in this test. With these new SNPs, we are seeing the Phy­logenetic Tree for Y-DNA explode! There will be more Haplogroup subclades than ever before, thus helping testers determine in detail who is more closely related as well as providing younger and more geographically relevant Y-DNA branches. It not only refines the twigs (subclades) on the Y-DNA tree, it will also define the relationships between those twigs (subclades). This level of SNP testing will provide a much more accurate age for Y-SNP-based lineage to better clarify Bronze Age migrations from late Neolithic migrations, which is im­portant in understanding early history and pre-history.

This article appeared in the GFO Bulletin, Volume 64, No. 2, December 2014.

GFO is the Genealogical Forum of Oregon in Portland Oregon.  See their website:  www.gfo.org

For more information about DNA, please con­sider getting Emily’s book, Genetic Genealogy: The Basics and Beyond which can be purchased online at AuthorHouse.com, Amazon.com, and Barnes and Noble in paperback or as an e-book. The book can be ordered at any bookstore.

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