DNA Testing
A DNA test is now a key genealogical tool, but the market is crowded and full of hype, competing claims and jargon. Fortunately Debbie Kennett can help you spend your money wisely
Our complete buyer’s guide to testing kits cuts through the hype and jargon so you can make the right decision
DNA testing has taken off in a big way in the past two years – we regularly see stories in the media about people using DNA to trace their relatives, and earlier in the year even the cast of the nation’s most popular soap opera got involved thanks to the peak-time ITV programme Coronation Street’s DNA Secrets.
Somewhere in the region of 20 million people have now been tested, with thousands being added to the databases every day. Even if you haven’t yet taken the plunge, you will find that many of your relatives are already in the databases. And all the companies have big sales in the run-up to Christmas, so there’s never been a better time to start out on your own DNA journey.
However, a DNA test on its own is not very informative, and cannot tell you who you are or where you came from. DNA testing is best used as a tool for your family history research in combination with documentary records. The power of genetic genealogy lies in the comparison process. You need to work with your matches in the databases, and compare family trees in order to identify a common ancestor. DNA testing is also very useful for verifying your family history research. It can be very satisfying to have DNA evidence as additional confirmation of relationships, but you need to be prepared for a few surprises along the way. For this reason, when testing your relatives it’s important to ensure that you gain their consent, and that you warn them of the possibility of unexpected results. The Genetic Genealogy Standards Committee provide some useful guidance that you can download from geneticgenealogystandards.com as a free PDF.
There are many possible scenarios where DNA testing can be helpful. Do you have a brick wall with an illegitimate grandfather? Is your sister a full sibling or a half-sibling? What happened to your cousins who emigrated to America or Australia? DNA is increasingly being used to solve such mysteries. For some scenarios you will need to identify the appropriate people to test and then compare the results to determine whether the shared DNA is consistent with the expected relationship. If you’re trying to make contact with longlost relatives, add your DNA to all of the databases and hope that the right matches turn up.
Of course, the person that you’re looking for does not have to actually be in the databases – in unknown parentage searches, matches with first and second cousins can often provide the answers. You might not get the right matches straightaway, but your results stay in the databases and there is a good chance that one day you will get the breakthrough you need.
Taking the Test
The DNA test itself is completely harmless, and can be done in the comfort of your own home. Depending on the test you order, you will have to provide a cheek swab or a spit sample.
There are three different types of test – autosomal DNA, Y-chromosome DNA and mitochondrial DNA – all of which have specific applications. The choice of test will depend on the questions that you want to answer, and sometimes a combination of different tests will be required to solve your particular mystery.
Autosomal DNA Testing
The autosomal DNA test is now the most popular of the three tests, accounting for the vast majority of sales, and tests the autosomes that we inherit from both of our parents. These are the chromosomes other than the two sex chromosomes (X and Y) that contain most of our DNA sequences and genes. Autosomes come in pairs, and we receive one set of 22 autosomes from our mother and one set of 22 autosomes from our father. Before the DNA is passed on it is shuffled up in a process known as recombination. The DNA we inherit from our parents is therefore a patchwork of DNA from all four of our grandparents.
We inherit 50 per cent of our DNA from each of our parents, and we share approximately 25 per cent of our DNA with our four grandparents. However, the amount of DNA inherited from an individual grandparent can vary. We might share 30 per cent with one grandparent and 20 per cent with another, but the average shared with all four will always work out at 25 per cent.
‘The choice of test will depend on the questions that you want to answer’
While autosomal DNA provides a representation of all of our different ancestral lineages, the amount of sharing is diluted with each generation. Beyond the second-cousin level there are some cousins with whom we do not share any DNA, and after about six or seven generations we have ancestors with whom we share no DNA: they are our genealogical ancestors, but not our genetic ancestors. There is only a slim chance of sharing a match with a specific fifth or sixth cousin, but we have so many distant cousins that they dominate match lists.
The matches are worked out by looking at the number and size of shared DNA segments. In general, the more segments that are shared and the longer they are, then the closer the relationship. Autosomal DNA tests can accurately identify relationships up to the secondcousin level, but it is more difficult
‘It is more difficult to verify relationships beyond about five or six generations’
to verify relationships beyond about five or six generations because of the wide range of possible relationships and the limitations of genealogical research. If you only share a single small segment then your match could be your fifth cousin or your 15th, but we have no way of knowing which is which.
With DNA testing, it always helps to start with the known to get a feel for how the tests work, and then move out to the unknown. So you should try to encourage as many close relatives to get tested as possible. If you test your parents, for example, then you will be able to partition your matches onto the paternal and maternal sides. If your first or second cousins test, then you will know that any matches you share with your cousins must be related through your common grandparents or great grandparents. The more matches you are able to confirm with known relatives then the easier it becomes to work out the unknown relationships. Always focus on your top matches where you stand the best chance of making connections.
Y-DNA
Y-chromosome DNA (Y-DNA) is passed on by a father to his sons, and the transmission usually follows the inheritance of surnames. This test can therefore only be taken by males. Females will need to find a suitable candidate for testing such as their father, brother, uncle or cousin.
For genealogical purposes markers known as short tandem repeats (STRs) are tested. These
are repeating sequences of DNA letters. The number of repeats is added up, and for each marker you are given a number. Then your numbers are compared with the other people in the testing company’s database, and you are given a list of the Y-DNA matches whose numbers most closely match yours. The 37-marker test is the standard entry-level test, but tests are also available with 67 and 111 markers.
Y-DNA testing can be used to verify existing research, to explore which different surname lineages are related and to investigate variant spellings. A Y-DNA test will provide evidence of a link even if there are no surviving genealogical records to determine how the two lines are related. Y-DNA test results are best co-ordinated within a structured surname project, where the results can be clustered into ‘genetic families’.
Y-DNA can also be used to trace illegitimate lines. A match with a different surname might provide a clue to the identity of the biological father.
In addition a Y-DNA test gives information about your deep ancestry through the haplogroup assignment. A haplogroup is a branch on the Y-chromosome tree. Each haplogroup has its own distinct geographical distribution. The haplogroup is predicted from the STR results, but a more refined haplogroup assignment can be obtained by testing different types of markers known as single nucleotide polymorphisms (SNPs). Some companies include Y-DNA haplogroup information in their test, but this can’t be used for genealogy. More comprehensive Y-chromosome next-generation sequencing tests are now available, which provide information on both SNPs and STRs in a single test. These tests are still quite expensive, but as the cost comes down will eventually replace the need for separate tests.
Mitochondrial DNA
Mitochondrial DNA (mtDNA) is passed on by a mother to both her sons and daughters, but only females can pass on their mtDNA to the next generation. An mtDNA test can therefore
be taken by both males and females, and is used to explore the direct maternal line, or ‘matriline’ – your mother, your mother’s mother, your mother’s mother’s mother and so on. However, it is not so easy to use mtDNA testing for genealogy because the surname changes with each generation, which makes it more difficult to identify potential cousins for comparison purposes. Also, mtDNA mutates very slowly. This means that, even if you have a very close match, the common ancestor might have lived 1,000 years ago – or more. Nevertheless mtDNA can be helpful when used with autosomal DNA testing to rule matches in or out on the matriline.
With an mtDNA test you will also get a haplogroup assignment, which will provide information about the deep ancestral origins on your matriline. The various haplogroups have distinct geographical distributions, and can sometimes provide important clues in their own right. For example, haplogroup M is commonly found in India, so if someone of British ancestry were to test with haplogroup M it would potentially open up a new line of enquiry in the former British India. Some companies include mtDNA haplogroup information in their test, but you need to have a matching database in order to use mtDNA for genealogy purposes.