A Beginners Guide to Using DNA in Family History


Margaret Jordan advises

When you hit the proverbial ‘brick wall’ in family history research, DNA testing can come to the rescue in many cases and it can help to solve mysteries. It can also uncover new mysteries such as non-paternity events (NPE).

It is important to understand the basics before embarking on genetic testing for family history so that you know what it can and cannot do [www.dna-testing-adviser.com]. There are three main types of testing used in family history research: mitochondrial DNA (mtDNA), autosomal DNA (atDNA) and y-chromosome DNA (yDNA).

We all have mitochondrial DNA (mtDNA) which is passed down by a mother to all her children. However, males do not pass on their mtDNA to their children, so the value of mtDNA testing is in tracing back along a maternal line (your mother, her mother and so on). Unfortunately, mtDNA doesn’t generally follow a surname as women traditionally changed their surname on marriage.

Autosomal DNA (atDNA) can be inherited from any line. Therefore, it can find matches in any branch of your family tree but it works better when two people share a recent ancestor.

Only men have y-chromosome DNA (yDNA) which is passed down from father to son. yDNA mutates very infrequently, and therefore it can be used to trace a biological paternal line. The most significant benefit of using yDNA in genealogical research is that the surname is generally co-inherited with the yDNA.

As yDNA is currently the most useful and universally used DNA tool in family history research I will focus on this.

The diagram shows how yDNA is passed down from father to son.

dna diagram1

There are many reasons for considering yDNA testing. You may be in the New World and trying to trace your paternal ancestry back to your Irish origins or living in Ireland and looking for descendants of relatives who left Ireland in Famine times. You may be trying to establish a connection with a particular family line or you may be researching your surname in general.

DNA testing can be as simple as a mouth swab, done at home and the sample mailed back to the testing company. The first thing is to decide what you hope to achieve and which family surname you want to research. Then you need to select a male with that paternally inherited surname and choose a testing company.

Family Tree DNA [www.familytreedna.com] which is based in Texas, USA is the testing company with which I am most familiar. Each surname study at Family Tree DNA is managed by voluntary administrators who help participants with understanding their results. For example, the O’Shea yDNA Project [www.familytreedna.com/group-join.aspx?Group=OShea], which I have been involved with since it started in 2003, was set up to study the O’Shea Surname using yDNA. Participants generally start with a 37 marker test and upgrade to 67 markers if required. If no suitable Irish surname yDNA project is available for your particular surname at Family Tree DNA, the Ireland yDNA Project [www.familytreedna.com/project-join-request.aspx?group=IrelandHeritage&projecttype=G] acts as an umbrella project for all men with Irish ancestry on their paternal line.

When the decisions have been made and the kit ordered, the mouth swab is done a few hours after eating and the sample returned to the testing company. Then all you have to do is wait patiently. After a few weeks, the yDNA results will be sent to you by email. The results comprise a set of numbers (y-haplotype) relating to the number of short tandem repeats (STRs) on each marker tested, on the y-chromosome. Then the excitement of seeing with whom you match begins. The testing company lists the names of your close matches along with their email addresses. The statistics involved in analysis of yDNA results can provide two people with an estimate to how far back their common ancestor might be. However, yDNA testing cannot tell you what is the exact relationship between two people.

Making contact with people you match across the globe can be exciting. You can compare notes to try to find your common ancestor. People who match each other often share photos and may meet up. This forges links between the Irish Diaspora and those still living in their native homeland. People talk euphemistically about a ‘non-paternity event’ (NPE) when yDNA results are not as expected. On the other hand, some people have questions regarding adoption in their family and yDNA testing can help them find their biological surname.

For the enthusiast, testing SNPs (Single Nucleotide Polymorphisms) can provide further information on the migration of your ancestors, over thousands of years. The National Genographic Project [https://genographic.nationalgeographic.com], started by Spenser Wells in 2005, studies this migration of people from Africa about 60,000 years ago to all areas of the globe.

In conclusion, DNA testing can be exciting and surprising. Finding genetic cousins can open up new lines of communications across continents. Adding the genetic genealogy tool to your family history research armoury adds an exciting dimension and can produce some interesting twists.

[Margaret Jordan is a Member of the Association of Professional Genealogists in Ireland, and is joint co-ordinator of the Ireland yDNA Project.]