Choose the DNA test that’s right for you with our buyer’s guide
DNA testing has been transformed from a niche hobby to a multi-million dollar industry. With so many options, how do you decide which test to take and which company to use? Debbie Kennett provides expert guidance
DNA testing is a very important tool for the family historian. It can help to verify your family tree and provide helpful clues to inform the future direction of your research. It can also sometimes help to break down those long-standing brick walls.
DNA has the power to solve previously impossible cases. Foundlings, adoptees and donor-conceived individuals now have a very real chance of finding half-siblings and other close relations in the databases, which can lead to the identification of their biological parents. If you have a match with a second cousin, it means that you share the same great grandparents. It’s then just a question of tracing the descendants to identify a suitable candidate who was in the right place at the right time. Success stories are reported on a daily basis in America and we’re now starting to get reports from the UK as well. As the databases grow, we can expect to see many more unknown parentage cases solved. DNA discoveries As with traditional genealogical research, DNA testing can provide surprises so be prepared for the unexpected. You might uncover family secrets by matching with a cousin or a half-sibling that you didn’t know existed. Conversely a relation who is expected to share DNA with you might turn out not to be a genetic relative at all. In rare cases, people discover that their parents are not their biological parents. For a good overview of the ethical implications of DNA testing see the Genetic Genealogy Standards ( geneticgenealogystandards.com). However, DNA testing is not a magic bullet and it won’t provide you with an instant family tree. Contrary to popular belief, you cannot take a DNA test to discover who you are and where you come from. The value of the test lies in the comparison process, so it’s important to test with a company that has a matching database. DNA is best used in combination with genealogical records in order to form conclusions about relationships. The test itself is completely harmless; you just need to provide a cheek swab or a saliva sample.
The choice of test will depend on the questions that you want to answer, or you can just take a test for fun to see who you match in the databases. A DNA test can be considered as an investment and the value of the test will grow as more people join the databases and you get more matches.
There are three different types of test – autosomal DNA, Y-chromosome DNA and mitochondrial DNA – all of which have specific applications. Sometimes a combination of different tests will be required to solve a particular problem.
AUTOSOMAL DNA
DNA is packaged up inside chromosomes. Humans have 23 pairs of chromosomes which comprise 22 pairs of autosomes and one pair of sex chromosomes – the X
chromosome and the Y chromosome. One set of chromosomes is inherited from our mother and one from our father. Males inherit a Y chromosome from their father and an X chromosome from their mother. Females receive two X chromosomes, one from each parent.
Autosomal DNA, the DNA inherited on the autosomes, is shuffled up in a process known as recombination. The DNA we inherit from our parents is a patchwork of DNA from all four of our grandparents, which in turn is a mosaic of DNA inherited from earlier generations. We share half of our DNA with our parents, and around a quarter with our grandparents. However, because of the random nature of the inheritance process the amount of DNA inherited from specific ancestors can vary. We might inherit 29 per cent of our DNA from one grandparent but only 21 per cent from another.
Autosomal DNA tests can be taken by both men and women. They work by comparing the size and number of shared segments of DNA and making predictions about relationships. First cousins share around 12.5 per cent of their DNA while second cousins share around 3.13 per cent. Beyond the second cousin level, there are some cousins with whom you might have a legitimate genealogical relationship, but neither of you will have enough segments of DNA in common to show up as a match. There is only a slim chance of sharing a match with a specific fifth or sixth cousin. However, because we have so many fifth to distant cousins these will dominate your match list. Finding the genealogical relationship can be challenging: the match could be on any ancestral line and few people are able to identify all their ancestors on every single line going back for more than about four or five generations. Autosomal DNA is therefore best deployed to find and verify matches with close relations who are no more distant than perhaps fourth or fifth cousins. Wherever possible you should test the oldest generation to maximise your chances of finding matches. If you can’t test your parents then test your siblings as they
will pick up matches with some cousins who won’t show up in your own match list.
The first cousin-matching autosomal DNA test became available in November 2009 and it’s now the most popular test accounting for the lion’s share of sales. Each company will give you a list of your genetic cousins and the predicted relationship ranges. It is then up to you to compare trees with your matches and see if you can identify the ancestral couple you have in common. The thresholds for what constitutes a match vary from one company to another, and they each offer a different range of tools to help with the analysis. If you are testing in the hope of finding a breakthrough match to solve a brick wall it helps to be in all the databases, as you never know where the key match will come from.
Chromosome mapping
It can be fun to test lots of relatives so that you can map out which segments of DNA have been inherited from specific ancestors. This process is known as chromosome mapping and to do this you need to test with a company that provides a chromosome browser and lets you download the matching segment data.
An autosomal DNA test will also include a biogeographical ancestry analysis. These reports compare your DNA with reference populations from different countries and will give you the percentages of your DNA that match with the reference populations. This type of analysis is still in its infancy, and only a limited number of reference populations are available. If you have ancestry from a particular population and it is not included in the dataset then you will be matched with the next closest population. These tests can reliably distinguish between European, Asian, African and Jewish DNA, but cannot differentiate DNA at the country level so do not expect the percentages to correspond with your genealogical ancestry. Each company uses its own algorithms and has a proprietary database supplemented with samples from publicly available datasets. If you test with a number of companies you will find that you get markedly different results. Siblings will often get very different results too, though this is partly explained by the fact that they inherit different proportions of DNA from their parents. These reports will improve over time as more reference populations become available and as the methodology is improved.
Living DNA ( livingdna.com), a new British company, has recently rolled out a test which is able to provide regional breakdowns within Britain and Northern Ireland with reasonable accuracy. AncestryDNA ( ancestry.co.uk/dna) is rolling out a new feature which uses
sophisticated networking algorithms to assign people to genetic communities and provides a good level of regional resolution, especially in Ireland. You can expect to see the reports from the other companies updated free of charge in due course too. Y-DNA Y-chromosome DNA ( Y-DNA) is passed on by a father to his son, 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 STRs (short tandem repeats) 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. Your numbers are then compared with the testing company’s database and you are given a list of your Y-DNA matches whose numbers most closely correspond with yours. The 37-marker test is standard, but tests are also available at 67 and 111 markers.
Y-DNA testing can be used to verify existing research, to explore which different lineages are related and to investigate variant surname 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 coordinated within a structured surname project where the results can be assigned to “genetic families”. Y-DNA can also be used to trace illegitimate lines. A match with a different surname might provide an important clue to the identity of the biological father.
A Y-DNA test also provides 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 SNPs (single nucleotide polymorphisms). Haplogroup information is interesting for deep ancestry purposes, but currently has little direct genealogical application.
Comprehensive Y chromosome next generation sequencing tests are now available which have potential relevance, but multiple comparisons are required to determine the branching patterns of the SNPs. About 15,000 or so pioneering males have taken this type of test, but the cost is still beyond the means of the average family historian.
A Y-DNA test will provide evidence of a link even if there are no surviving records
MITOCHONDRIAL DNA Mitochondrial DNA 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 – your mother, your mother’s mother, your mother’s mother’s mother and so on. It is not so easy to use mtDNA testing for genealogy because the surname changes with each generation, making it more difficult to identify potential cousins for comparison purposes. Furthermore, mtDNA mutates very slowly which means that, even if you have an exact match, the common ancestor might well have lived a thousand or more years ago. mtDNA can be helpful when used in combination 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 your 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.
If you’ve not yet started on your genetic journey, I hope I have inspired you to take the plunge. Although DNA testing might sound complicated, it starts to make sense when you have your own DNA results and can apply them to your research. It’s exciting to find evidence of a genealogical connection and to make contact with genetic cousins around the world. The science is constantly advancing so look out for new developments in the months and years to come.