Genetic Genealogy

(Published in Fife Family History Society journal No. 2 Winter 2004)

 

DNA testing is a technique which is very much in its infancy as a method of family history. What are the possibilities for using our DNA to prove or disprove family connections?

DNA (deoxyribonucleic acid) is the chemical within our cells which determines our inherited characteristics, and carries all the instructions for creating a human being. DNA consists of four "letters" - A, C, G and T. Each three letter group is the code for one amino acid, which are some of the main building blocks of life. There are many millions of these letters in each person's DNA, but only 0.2% of these differ.

There are three main types of testing at the moment - testing of autosomal, mitochondrial and Y chromosomal DNA. The first of these, genetic fingerprinting of our autosomal DNA, of the type used in forensic investigations or paternity tests, is of very limited use to a family historian. It is only good at determining very close family relationships, since we only inherit half of our DNA from each parent. We only share ¼ of our DNA with each of our grandparents, and 1/16 with first cousins. It becomes difficult to prove a connection which is more than a few generations apart.

Mitochondrial DNA (mtDNA for short) is a type of DNA which is passed unchanged from mother to child. It is found in the mitochondria - the powerhouses of our cells. Testing of the mtDNA can only be used to investigate the maternal line, because none is inherited from the father (he does receive mtDNA from his mother, but does not pass it on to his children). If a match in the mitochondrial DNA of two people is found, it proves that their maternal lines converge in one woman at some point in the past 10,000 years - a much larger time scale than is of use to the family historian who wants to know whether there was a connection in the past 500 years or so. However, the chance of the mitochondrial DNA of two people chosen at random matching is only 2%, so it may be useful corroborating evidence. Our mitochondrial DNA can also tell us something about where in the world our maternal line originated, which is interesting but not necessarily of help in researching our family tree.

The most useful type of DNA to the family historian is that carried on the Y chromosome. This is passed unchanged from father to son - daughters do not inherit it. It's particularly useful to people who are interested in tracing their paternal line, or to those carrying out one-name studies. Testing of this type of DNA can determine whether there was a common ancestor within the past 16 generations or so - a much more useful timescale. The more markers, or locations, on the DNA, that are tested, the more useful the result.

DNA testing is still prohibitively expensive as far as many of us are concerned. It costs about £150 to test one person's DNA, and the same amount for each additional person whose DNA you want to compare. A large number of companies are springing up which specialise in testing DNA for family history purposes, and generally they will send out a kit to enable you to take the sample yourself, which is then sent back to the laboratory for testing. DNA testing usually involves scraping a small sample of cells from the inside of the cheek - a painless process. Different companies test different markers in the DNA, and some test more markers than others.

Although it is possible to obtain DNA from old bones, and it has been collected from some very ancient bones indeed, most of us would find it disrespectful to dig up our ancestors to test their DNA. So we have to rely on people who are living to provide the DNA samples. We can find out about lines other than the direct maternal or paternal lines through the DNA of aunts, uncles, cousins and more distant living relatives.

Perhaps one day it will be possible to put everyone onto one huge genetic family tree. Many people are already posting their DNA profiles on the internet, in the hope of finding relatives, and some of them have. But it may be decades before an amount of data comparable to that held in family tree databases is amassed, and there is no one overall database on which to compare your results.

DNA testing needs to be used with care so that people don't make leaps of imagination about their shared ancestry. DNA can tell us we have a common ancestor, but not in which generation that ancestor is to be found - it can only give probabilities.

Of course genetics can tell us nothing about the way our ancestors lived, or what experiences they had over the course of their lifetimes, so there is still plenty of work for us to do using traditional family history research methods!

 

Recommended reading:

 

Books:

The Seven Daughters of Eve, by Bryan Sykes

In the Blood - God, Genes and Destiny, by Steve Jones

 

Websites:

Rootsweb mailing list -

http://lists.rootsweb.com/index/other/DNA/GENEALOGY-DNA.html

 

Chris Pomery's DNA Portal -

http://freepages.genealogy.rootsweb.com/~allpoms/genetics.html