Autosomal DNA is a term used in genetic genealogy to describe DNA which is inherited from the autosomal chromosomes. An autosome is any of the numbered chromosomes, as opposed to the sex chromosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes (the X chromosome and the Y chromosome). Autosomes are numbered roughly in relation to their sizes. That is, Chromosome 1 has approximately 2,800 genes, while chromosome 22 has approximately 750 genes. There is no established abbreviation for autosomal DNA: atDNA (more common) and auDNA are used.
Autosomal DNA testing
Autosomal DNA tests for genetic genealogy are provided by 23andMe, Family Tree DNA (the Family Finder test) and AncestryDNA. The Family Finder test and the AncestryDNA tests are both genealogical DNA tests which give you matches with genetic cousins and also give you admixture percentages. The 23andMe test is a genealogical DNA test but also provides information on health and traits. The cousin-finding element of the 23andMe test is known as DNA Relatives (formerly Relative Finder). The 23andMe health reports were suspended for customers who purchased the 23andMe test after November 2013 due to FDA regulatory intervention, but the health reports were reintroduced for customers in Canada in October 2014 and in the UK and Ireland in December 2014.
The AncestryDNA test is only available in the United States, the United Kingdom, Ireland, Canada, Australia and New Zealand. The 23andMe test is available in 56 countries. The Family Finder test is available worldwide. For further information see the article on shipping DNA kits, which includes information on shipping costs together with a list of package forwarders. Note that if you are in the US and live in New York or Maryland you will not be able to order a 23andMe test, though you will be able to purchase the AncestryDNA test or the Family Finder test.
Autosomal tests are also offered by the Genographic Project (Geno 2.0) and BritainsDNA but these tests will only provide you with ethnicity percentages and cannot be used for genealogical purposes and do not give you matches with genetic cousins.
For a comparison of the autosomal DNA testing services see the autosomal DNA testing comparison chart.
Accuracy of tests
Autosomal DNA tests can be used to confirm relationships with a high level of accuracy for parent/child relationships and all relationships up to the second cousin level. For all relationships other than parent/child relationships additional contextual and genealogical information is required to confirm the nature of the relationship.
For genealogical relationships between second cousins once removed and 5th cousins a more careful approach is necessary and data needs to be collected from multiple family members. For relationships at the 4th cousin once removed to 5th cousin level you may need to test 10 to 20 or more first and second cousins and see how much autosomal DNA they share with a potential 4th cousin once removed or a potential 5th cousin in order to have sufficient data to generate a statistically significant average amount of autosomal DNA that is shared among the entire group, assuming that you are dealing with a non-endogamous population. See Tim Janzen's summary at http://blog.23andme.com/ancestry/who-were-the-parents-of-jacob-youngman for an example of this type of quantitative approach. For endogamous populations, genealogical relationships are frequently difficult to estimate beyond about the 2nd cousin level of relationship and require careful analysis.
Genealogical relationships beyond the 5th cousin level of relationship are more difficult to prove with autosomal DNA testing and, as a general rule, these can only be approached using triangulation. In some cases Y-DNA and mtDNA data may also be of help.
Who to test?
For autosomal DNA testing one should always test the oldest generations first wherever possible - your parents, grandparents (if you are lucky), aunts and uncles. By testing yourself as well as your parents you will be able to determine which segments have been inherited from which parent, and you will also be able to rule out coincidental (Identical by state) matches. A two-parent/child trio also provides the best results for the purposes of phasing and chromosome mapping.
If you only have one parent available for testing then you should test you and your parent. You should also test your siblings because they will inherit part of your parents' DNA that you don't carry.
Your uncles and aunts will inherit part of your grandparents' DNA that your parents don't have.
The next priority should be to test other close relatives from first to third cousins to get the best representation across your ancestry. Experience suggests that the maximum return is obtained by testing second cousins. They share one set of great grandparents so when someone matches you and a second cousin you get to narrow down your matches to that specific line.
For the purposes of chromosome mapping you would need to test four 2nd cousins in order to get the same amount of DNA mapped as would be the case if you just tested one first cousin. However, the segments mapped with second cousin data would be attributed back two generations whereas the segments mapped with first cousin data can only be attributed back one generation.
Introduction to Autosomal DNA
Maurice Gleeson provides an introduction to autosomal DNA testing and the matching process in the following video:
Autosomal DNA for beginners
- Introduction to atDNA by Kelly Wheaton. Lesson 5 in the series "Beginner's guide to genetic genealogy", Wheaton Surname Resources website, 2013.
- SNPs and segments by Kelly Wheaton. Lesson 6 in the series "Beginner's guide to genetic genealogy", Wheaton Surname Resources website, 2013.
- Ancestral origins Part 1 by Kelly Wheaton. Lesson 7 in the series "Beginner's guide to genetic genealogy", Wheaton Surname Resources website, 2013.
- Ancestral origins Part 2 by Kelly Wheaton. Lesson 8 in the series "Beginner's guide to genetic genealogy", Wheaton Surname Resources website, 2013.
- atDNA matches by Kelly Wheaton. Lesson 9 in the series "Beginner's guide to genetic genealogy", Wheaton Surname Resources website, 2013.
- DNA testing for genealogy - getting started Part 3: autosomal DNA by CeCe Moore, Geni.com blog, 1 August 2012
- DNA testing for genealogy - getting started Part 4: ethnicity breakdowns by CeCe Moore, Geni.com blog, 8 August 2012
- Choosing the right autosomal DNA test shouldn't be a random process by Dr Tim Janzen, 8 October 2012
- Exploring the Use of Autosomal DNA for Genealogical Purposes by Dr Tim Janzen, 16 October 2012.
- Understanding autosomal DNA testing by Steve Handy. DNA Genealogical Experiences and Tutorials blog, 21 October 2012.
- How much DNA do distant cousins actually share? by Henry Louis Gates and CeCe Moore. The Root, 14 Novembre 2014.
- Successfully using autosomal testing in conjunction with mitochondrial and Y-line testing to address genealogical questions An essay by Roberta Estes, 2007-2009. The paper was originally written for people searching both genealogically and genetically for their Native American ancestors and heritage, but the techniques described will also apply to those searching for any minority heritage.
- Autosomal DNA by Angela J. Cone
- A Beginner's Adventures in Genetic Genealogy by Paddy Waldron (a work in progress)
- A methodology: identifying your relatives through your atDNA results with thanks to Diane Harman-Hoog, the original author of this methodology; Karin Corbeil co-developer;and Mesa Foard, technical writer.
- Genealogy and autosomal DNA matches: common errors in proving an ancestor and the allure of easy gateway ancestors Genealogy and Genomics blog, 19 April 2015.
- Organising your autosomal DNA information with a spreadsheet by Jim Bartlett, 17 January 2014 (a guest post on Kitty Cooper's blog).
- Succeeding with autosomal DNA by Jim Bartlett, 24 June 2013
- What to do with your DNA test by Kitty Cooper, 19 November 2013.
- Using your autosomal DNA test results: the basics for genealogists by Kitty Cooper, 18 March 2015.
- Autosomal DNA testing is now affordable for all by Debbie Kennett, Cruwys News blog, 7 August 2013.
- Non-genetic relatives in a DNA database by Jim Owston, The Lineal Arboretum blog, 26 May 2013
- The atDNA gamble: playing the odds by Judy G. Russell, The Legal Genealogist, 2 September 2012.
- The common mismatch by Judy Russell, The Legal Genealogist, 1 September 2013.
- DNA Dilemma: Should I Take a Genetic Test? A week-long series of articles by Newsweek reporter Mary Carmichael with views and comments from a wide range of contributors including some ISOGG members, 2 August 2010.
- DNA Adoption The DNA Adoption website has many useful resources. Although the website was primarily set up to help adoptees get the most out of their autosomal DNA results, the methodology described is equally applicable for genealogists.
- Sex doesn't matter any more: an autosomal DNA primer A handout to accompany a webinar presented by Judy G Russell on 30 April 2013 for the Association of Professional Genealogists.
- Autosomal DNA A video from the Sorenson Molecular Genealogy Foundation now hosted on the Learn Genetics website
- Relatedness by Dr. Erin Cline Davis, a science writer at 23andMe, Ask a geneticist, 10 October 2008.
- NY and MD limits on 23and Me by Judy G. Russell, The Legal Genealogist, 23 December 2012.
- That pesky NY law by Judy G. Russell, The Legal Genealogist, 23 June 2013.
- Autosomal DNA portal
- Admixture analyses
- Autosomal DNA statistics
- Autosomal DNA testing comparison chart
- Autosomal DNA tools
- Before You Buy
- Chromosome Browser Examples
- Chromosome mapping
- DNA Relatives
- Family Finder
- Fully identical region
- Half-identical region
- Identical by descent
- Identical by state
- Personal genome test proactive successes
- Shipping DNA kits
- Understanding genetic ancestry testing
- X chromosome testing
|This article uses material in the public domain from the Talking Glossary of Genetic Terms and is reproduced courtesy of the National Human Genome Research Institute.|