Posts tagged ‘AncestryDNA’
Autosomal DNA is inherited by both males and females and received equally from each of our parents.
In commercial genetic genealogy tests our autosomal DNA is compared against a large database of others, looking for identical segments of inherited DNA that may indicate we have shared ancestors.
Some questions that might be answered by an autosomal test include:
- Can I find previously unknown cousins, solely from my DNA?
- Can I look for relatives on all branches of my pedigree (not just my father’s patrilineal or my mother’s matrilineal lines)?
- Can I test the accuracy of the family tree I have constructed?
How does it work?
Autosomal DNA tests examine 22 of the 23 pairs of chromosomes that we inherited from each of our parents. The remaining pair (called the ‘sex chromosomes’) determines gender. (X-chromosome analysis is often also reported in autosomal tests.)
We inherit about half our autosomal DNA (atDNA) from each of our parents and so about one quarter from each of our grandparents (and an eighth from each of our great grandparents…) – eventually we may not have enough DNA from a particular ancestor to be recognisable.
Close relatives share large segments of atDNA that each has inherited from a recent ancestor in common. More distant relatives may carry smaller sections of identical DNA. Commercial DNA testing companies predict the approximate relationship between genetic cousins based on the size and number of shared identical segments of autosomal DNA. (Very small pieces of atDNA in common are more likely to be coincidental rather than inherited.)
Because of randomness each time autosomal DNA is passed on, even siblings do not have identical autosomal DNA inherited from their parents and the amount of atDNA shared between relatives can vary greatly. As the amount inherited from a particular ancestor diminishes over the generations, eventually two distant cousins may not share enough DNA for a commercial test to identify them as genetic relatives.
While first and second cousins (and closer relationships) should be recognised in an autosomal test, and third cousins are extremely likely to be identified, only around half of fourth cousins will be found by their atDNA. By the time of fifth cousins, only about 10-15% will be recognised and by sixth cousins, only about 2-5% will be identified as genetic relatives.
Because of this, the general rule of thumb is that best results from autosomal DNA tests occur when there is up to about 5 generations back to the shared ancestor. For those hoping to prove relationships beyond third cousins, it may be necessary to test more siblings or first cousins on one side (or both) in order to find a recognisable shared segment of inherited DNA.
Because of this ‘number of generations’ limitation, in autosomal tests it is better to test the oldest living family member (or the one who is in the earliest generation).
What do autosomal DNA test results look like?
The commercial companies’ autosomal tests generally report your matches in the database (and their contact details) with predicted relationships based on the amount of shared autosomal DNA.
Three main companies provide autosomal tests for genetic genealogy. Family Tree DNA calls their autosomal test ‘Family Finder’. 23andMe call their atDNA test ‘Relative Finder’. AncestryDNA also provides autosomal DNA testing.
Currently AncestryDNA does not provide any such chromosome information, directing those who test to look at the public trees of their matches, in the hope that shared ancestors can be recognised. ‘DNA circles’ link people who match DNA and who also have the same ancestor in their family trees.
Family Tree DNA and 23andMe provide ‘chromosome browsing’ tools, showing on which chromosome/s lie any shared segments. Because the test alone cannot distinguish which chromosome was inherited from a mother and which from a father, these chromosome maps appear as images showing only one of each pair of chromosomes. For instance, in the image below the background (dark) chromosomes are mine, and the segments I share with three close relatives are shown overlaying, in different colours.
Simplifying to only showing each pair as a single chromosome means that it might appear as if I match two people in the same area of the same chromosome but maybe I match one on the chromosome inherited from my mother and one on the chromosome inherited from my father. The two predicted genetic relatives may each match me but not each other. I should ask each to check if the other appears in their list of matches.
When a segment is shared between three or more people (meaning at least two besides myself and where each person also matches the others at that same location) then we share the same ancestor – this is called triangulation.
From the websites of all three companies (FamilyTreeDNA, 23andMe and AncestryDNA) one can download the raw autosomal test data in order to upload it to third party sites such as GEDmatch – which provide more tools for chromosome analysis as well as finding matches with those who tested with the other companies.
Admixture predictions are also based on autosomal DNA. Genetic admixture means the interbreeding of mixed population groups represented by our ancestors. This tends to be reported in a summary such as ‘30% British, 20% Northern European, …’. In fact this analysis is based on comparisons against databases which were probably created for other purposes than genealogy and the conclusions may not be accurate.
23andMe call their admixture analysis ‘Ancestry Composition’. Family Tree DNA calls theirs ‘My Origins’. AncestryDNA calls their admixture analysis ‘Genetic Ethnicity’. While these analyses might be interesting, the conclusions are not yet completely reliable.
What to do with the results?
Include in your profile information with the companies the surnames in your ancestry and where those ancestors lived. Contact others likely to be close relatives based on their autosomal testing – starting with those whose surnames or locations you recognise – or where some clue points to the relevant part of your ancestry. You may be able to identify where previously unknown genetic relatives fit into your family tree. Then you can begin to share photographs and information in the same way as with more traditional genealogical methods.
You can also test known second or third cousins in order to identify which portions of DNA you share with them, that must have been inherited from known ancestors, and then see if those same segments are also shared with potential matches identified in the database. This might help identify to which branch of the family a new suggested genetic relative belongs.
By testing the DNA of known relatives, you can also check the family tree you have constructed, to see whether DNA confirms the expected relationships.
Autosomal DNA provides another tool that genealogists can use to find relatives and prove relationships. Its benefit is that it is not restricted to a single line (patrilineal or matrilineal) but instead relates to all branches of our ancestry. Its limitation is that it might not be able to identify relatives with a shared ancestor more than about five or six generations earlier.
Traditional family history research involves looking for documents that name an ancestor – and hoping that everybody told the truth! By contrast, genetic tools that are now available to genealogists tell the truth but do not name ancestors – however they can be used to find relatives and to check the accuracy of our constructed family trees.
Why use DNA testing?
I have an ancestor who was adopted. When I eventually located his original birth certificate, no father was named. I developed a plausible theory about who his father might have been, but I could not find any record to prove or disprove my idea.
In another case my ancestor, John Etherington, a builder, sits at the top of one of my ancestral lines but I cannot find any documentary evidence that he was related to the John Etherington, also a builder, who lived two streets away. Another ancestor, Samuel Etherington, was reputed to also be the Samuel Holmes who fathered another family. To solve puzzles such as these I needed a different set of genealogical tools.
What is DNA testing?
Genetic genealogy testing is all about comparing our DNA with others. Closer relatives share more DNA in common with us than more distant relatives. Genetic genealogy tests examine the areas of DNA where we differ – and predict approximately how closely we are related.
Sometimes we have a particular theory to check and we know in advance the two individuals we wish to compare. At other times genealogists are ‘fishing’ in the DNA ‘nets’, hoping to find unexpected genetic matches who might share an ancestor with us and who might then have information about unknown family branches. In the latter case there are benefits in comparing with as many people as possible. One way to do this is choosing a company with a large database of other people already tested.
DNA testing companies
Currently the main options for genealogists looking for living genetic relatives are the three US companies Family Tree DNA, 23andMe and AncestryDNA (a branch of Ancestry.com).
- Family Tree DNA is the company chosen by most genealogists – and these tend to respond to family history enquiries. Moreover this company’s website has useful tools available for comparing DNA as well as recorded webinars freely available.
- 23andMe offers genetic health predisposition reports as well as ancestry information. Many of their customers chose the company for those health reports and so are less interested in responding to genealogists. A dispute with the US Federal Drugs Administration (FDA) currently prevents 23andMe from providing health reports to new customers except in the United Kingdom and Canada.
- AncestryDNA tests were released first to US consumers and so most of the people in their database are in the United States. Recently AncestryDNA began offering tests to Australians. AncestryDNA test results can be linked to Ancestry trees.
Ordering a test involves going to the company’s website, selecting a test and paying by credit card and then the kit will be posted to you. Family Tree DNA and AncestryDNA tests involve swabbing inside your cheek (with something like a toothbrush) – in the way we have seen on television crime shows. The 23andMe test involves filling a test tube with saliva. In either method customers then post their completed kits back to the company and some weeks later are advised by email when their results are available online. Customers log on to the company’s website with a userID and password to find their results and matching customers predicted to be genetic relatives.
Which test should I take?
DNA testing is advancing (as well as becoming cheaper!) and so is more available for checking theories about your family history and perhaps even breaking down brick walls you might currently face. This article introduces the options currently available that might be useful to family historians.
Test 1: Y-chromosome tests, for males to test DNA inherited from their father’s fathers
For under US$200 we can test whether two males are likely to share a common ancestor ‘within a genealogical timeframe’, and how many generations ago that shared ancestor probably lived.
This test is valid for any two men who might share a male ancestor – they do not need to have the same surname. When testing with a company that has a huge database of people already tested, I might find a match with some living descendant who shares with me a common ancestor. This is useful for all genealogists but perhaps especially for adoptees.
I have used this test to discern whether two families with the same surname were actually related to each other, in the absence of documentary proof. I have also used this test to check (and refute) a theory about who might have been the biological father of an adopted male. It was necessary to find a living male descendant (down an all-male line) from the adopted male and also to find a living male descendant (down an all-male line) from the hypothesised birth father, and then compare the DNA that each inherited from their father’s fathers.
Y-chromosome tests are only available to males, as only males have a Y-chromosome. Females like me need to ask a near male relative to be tested – a brother, father, or uncle. I have ordered tests for my father and also my mother’s brother in order to examine my nearest male lines. For Y-chromosome tests, I recommend using the company FamilyTreeDNA and testing at least 37 markers.
Test 2: Mitochondrial tests, for anyone to test DNA inherited from their mother’s mothers
Useful DNA tests are no longer limited to males. We all have a different type of DNA (called mitochondria) that we inherited from our mother’s mother’s mother. Previously mitochondrial DNA could only tell us about ancient ancestors and their migratory patterns, but now it is possible to obtain much more recent information. Family Tree DNA offers a full sequence test of all our mitochondria, allowing us to identify people who share an ancestor with us on our maternal line within about 100-400 years. That test is also currently available for under US$200.
Test 3: Autosomal tests, to test the DNA inherited half from each of our parents
We are not restricted to testing only the DNA of our father’s fathers or our mother’s mothers. It is also possible to test our remaining DNA, inherited equally from both of our parents – this DNA is called ‘autosomal’. These tests compare the DNA of our ancestors regardless of gender, because we inherit half our autosomal DNA from each of our parents (and via them, from their ancestors). However as we inherit one quarter of our DNA from each of our grandparents (and so one eighth from each of our great grandparents) eventually the inherited material from any particular ancestor becomes so small as to be difficult to identify.
Consequently, when comparing this autosomal DNA with someone else, our best conclusions are when the shared ancestor lived no more than about five generations ago.
Commercial autosomal tests also report on our likely population origins or admixture, for example, ‘60% British, 20% Scandinavian and 20% Jewish’. The sample databases used for comparison are very small and currently most of these predictions are considered unreliable.
Family Tree DNA calls their autosomal test ‘Family Finder’, while 23andMe calls a similar test ‘DNA Relatives’. Both tests cost under US$100 – plus postage. (23andMe’s postage and handling charges to Australia adds another three quarters to the price of their kit!) The AncestryDNA test costs Australians under US$150 (plus postage) but if you do not have an Ancestry.com subscription there is an annual cost for accessing your results.
For any genetic relatives identified in their autosomal tests, Family Tree DNA and 23andMe also report on shared segments of the X-chromosome. Females have two X-chromosomes (inherited one from each parent) while males have one (inherited from their mother). When trying to work out which ancestral branch might have passed down the X-DNA we share with some match in the database, genealogists can look at pedigree charts and eliminate any father-to-son branches, as fathers do not pass any X-chromosomes to their sons.
Use the tests in conjunction
The tests can also be used in conjunction. The autosomal ‘Family Finder’ test through Family Tree DNA identifies matches with my DNA and calculates a likely relationship.
One of my matches (described as a possible 3rd to 5th cousin) seemed to have very similar Y-chromosome (father’s father’s) DNA to my mother’s brother. I made contact and by swapping names of grandparents and their parents we soon identified that he was the son of a 3rd cousin to me (and so indeed within the range of 3rd to 5th cousins).
Autosomal testing can be used to check your constructed family tree.
Comparing the autosomal DNA of the three female cousins (Fay, Ann and Maureen) at the bottom of this diagram confirmed my constructed family tree of their relationships back to their shared ancestors.
(Spouses omitted after the first generation to simplify the diagram.)
It is not necessary to understand how a car works in order to drive it, but it is necessary to know the functions of driving. In the same way it is unnecessary to understand much about the science of DNA – but it is necessary to understand what sorts of questions can be answered by the different DNA tests so you can use them as tools to aid your family history research.
The most recent DNA tests available to genealogists offer useful information which can supplement traditional genealogical methods. Family trees are still needed to identify ancestors and draw conclusions about relationships. DNA tests can supplement this genealogical research, filling in gaps in the paper trails. With such tools we can test our conclusions and assumptions in constructed family trees by confirming or disproving reputed relationships. As more people are tested and databases grow, commercial DNA tests are even more likely to help us find relatives that we might not have found by traditional methods.