As genetic genealogists we normally use DNA as a tool to help with our genealogical research. However, DNA testing can also provide some insight into one's deep ancestry. A man can take a Y-chromosome DNA test to explore his ancestry on the direct paternal line. Both men and women can take a mitochondrial DNA test to explore their ancestry on the direct maternal line. When you receive your Y-DNA or mtDNA results you are given a haplogroup assignment. The haplogroup represents your branch on the human Y-DNA or mtDNA family tree. Haplogroups are defined by markers known as SNPs (single-nucleotide polymorphisms) - small changes in the letters of the DNA alphabet. The Y-DNA tree is maintained by ISOGG - the International Society of Genetic Genealogy - and can be found here. The mitochondrial DNA tree is maintained by Mannis van Oven from the University Medical Center in Rotterdam in the Netherlands and can be found on the Phylotree website.
Haplogroups do tend to cluster in specific geographical regions and attempts can be made to explore the origins of these haplogroups by looking at their distribution and diversity in present-day populations, but there are inherent biases in the available databases, nowhere enough samples have been obtained and sometimes the conclusions drawn are highly speculative. Nevertheless many scientific papers have been published in peer-reviewed scientific journals on the origins of the different haplogroups, but with the discovery of more new markers on an almost daily basis these studies can often become out of date as soon as they are published. It can, of course, be fun to see who else shares your haplogroup. There is a page on Wikipedia which provides a list of the haplogroups of historical and famous figures, and there is also a famous DNA page on the ISOGG website. However, the markers that define these haplogroups often arose many thousands of years ago so it is therefore somewhat meaningless to declare, for example, that Tom Conti is directly related to Napoleon when they only share a common ancestor from several thousand years ago on their direct paternal line and they share that ancestor in common with thousands of other men in the same haplogroup. A DNA test cannot tell you that you are descended from a slave who was captured by the Vikings, and it is quite preposterous to tell someone that he is the ''grandfather of everyone in Britain" for many reasons not the least of which is that this ridiculous claim was based on a mitochondrial DNA test and males cannot pass on mtDNA to their children!
To counter some of these outlandish claims and to help the public to understand the issues involved the charity Sense About Science has produced a very useful new booklet entitled Sense About Genetic Ancestry Testing which can be downloaded from their website. The booklet has been written by a number of distinguished geneticists and explains very clearly the problems of assigning ancestry from a DNA test. Unfortunately some of the reports in the newspapers and online have commented on the publication of this booklet and given the story a somewhat misleading slant. The Telegraph has, for example, declared that "DNA tests [are] branded 'meaningless'" while the BBC more cautiously warns that "Some DNA ancestry services [are] akin to 'genetic astrology'". It is important to note that these headlines apply only to certain deep ancestry tests and not to the tests that we use for our genealogical research. As the Sense About Science authors note in their report:
"There are credible ways to use the genetic data from mtDNA or Y chromosomes in individual ancestry testing, such as to supplement independent, historical studies of genealogy. If, for example, two men have identified – through historical research, possibly involving surnames – a common maleline ancestor in the sixteenth century, it would be reasonable to use their Y chromosome data to test this. There are some ancestry testing companies that offer this service."I hope that lessons will have been learnt as a result of the Sense About Science publication and that the hyperbole of recent months will not be repeated. It is perhaps too much to hope that the press will take a more responsible attitude and will only publish stories based on scientific research published in peer-reviewed scientific journals rather than rehashing sensational stories from press releases submitted by PR companies as publicity stunts. In the meantime I would urge everyone to heed the words of Professor David Balding on the Sense About Science website: "Be wary of news items about genetic history - that someone famous is related to the Queen of Sheba or a Roman soldier. Often these come from PR material provided by genetic testing companies and can be trivial, exaggerated or just plain wrong."
If you wish to get your DNA tested either for genealogical purposes or to explore your deep ancestry there are a range of companies to choose from. The ISOGG Wiki has many valuable resources including a number of charts comparing the offerings of the various testing companies. Whatever your reason for taking a DNA test you will get the best value for your money if you choose a company which provides a genealogical matching database where you can contact your matches and get involved in projects. The two companies that I recommend are Family Tree DNA and 23andMe. Family Tree DNA host all of my DNA projects. They offer the widest range of tests and have by far the largest genetic genealogy database. They have over 7300 surname projects, a large number of geographical projects as well as projects for all the Y-DNA and mtDNA haplogroups. The 23andMe test is essentially a health and traits test but it also provides haplogroup assignments and it includes a cousin-matching service, known as Relative Finder, based on autosomal DNA. If you are interested in the 23andMe test you can read my reviews here.