GENETIC GENEALOGY

..... and What it Can Offer to Family Historians

By Rosemary Bailey

 This article was originally published in the December 2011 edition of Soul Search, the journal of The Sole Society

DNA testing can be used as a compliment to the traditional methods of researching family history.  The DNA is collected using mouth swabs, so no problem for the needle phobics amongst us.  There are three types of testing, all of which aim to answer different questions.

Y-DNA

This type of testing uses the Y chromosome which is only carried by men and is passed intact from father to son down through the generations.  So a man has the same genetic signature as his father, grandfather, great grandfather etc..  So if you find someone with the same Y chromosome, you share a common ancestor.

It would be too costly to look at all the DNA on the Y chromosome so the test looks at several parts, known as markers, which are highly variable between individuals.  Results are presented as a set of numbers for each marker.  The testing companies hold databases of results and if another researcher’s DNA produces the same set of numbers for all the markers then you probably share a common ancestor. A comparison of both trees might already show that ancestor, or it might be further back than researched at that time.  But at least you can collaborate on future research.

Because there are many testing companies and your results will only be compared against others using that company you will need to go further afield to look for matches. There are now genetic surname projects to which researchers of the same surname can submit their Y-DNA results to look for matches.

Because it uses the Y chromosome only men can take the test but if you are a woman researching your family history you could get your father, brother or other close male relative to take the test.

There are disadvantages to this type of DNA testing, the tests are costly, and at present the number of people tested is still relatively small so the chance of finding a match is low.  (It’s catch 22 situation, people don’t want to participate because the databases are small, but until people do take part they will remain small.)  And of course it’s never going to work if grandfather’s father was not great grandfather but actually the milkman!

Mitochondrial DNA (mtDNA)

MtDNA is passed from a mother to her children, both male and female, however males do not pass it on to their children but this does mean that both men and women can take the test. So a person’s mtDNA is the same as their mother, grand mother, great grandmother etc..

However at the  moment MtDNA is of little use to genealogists as it is a much deeper ancestry test and will reveal which of ‘The Seven Daughters of Eve’ you are descended from.  These are the seven women who 95% of the European population descend from and who lived between 10,000 and 45,000 BC.  So while that might be very interesting it’s not going to help you with more recent ancestry.

Fortunately research is suggesting that there are ways that mtDNA may be of used to give information about more recent ancestors and tests are being developed.

Biogeographical Tests

Another possibility is Bio Geographical or admixture test which breaks your geographic heritage into four broad chunks: European, African, Asian and Native American and gives you a percentage of each type.  So for instance a person may be 90% European, 6% African and 4% Asian. 

However there is a degree of probability in the results so they are not necessarily very accurate.  For anyone who tests at least 50% European there is now an advanced EuroDNA test that can break that portion down more accurately.