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Issue 85 - DNA Testing For Scottish Ancestry

Scotland Magazine Issue 85
February 2016

 

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DNA Testing For Scottish Ancestry

Dr Bruce Durie explains the basics of genetic genealogy

When I studied Molecular Biology classes at Edinburgh University back in the mid-1970s, I realised that I was learning things at the forefront of a very young discipline, but I hardly appreciated that what I learned about human DNA would feed into standard genealogical practice 40-odd years later.

DNA MADE SIMPLE

DNA is a remarkably simple molecule with only four components (called bases and labelled A, T, C and G), but the order and organisation of these “letters” makes “words” - the genes. A gene can be thousands of bases long, which is why it is possible to produce the equivalent of an encyclopaedia using words composed of only four letters in some order and length. DNA is the “knitting pattern” that contains the linear sequence of genes. Most cells in humans have a nucleus that contains 23 pairs of chromosomes – DNA packaged up with proteins – which contain the linear sequence of genes. These tell a cell which proteins to make, in which order and in what quantity. This therefore determines the nature of the tissue concerned and in turn, the form of the whole organism.

Genes are inherited from the parents and recombine (swap parts of themselves) so as to produce an individual who is half-and-half from the father and the mother; however the recombination makes each offspring (except identical twins) slightly different from its siblings. However, the DNA of all of us bears our individual genetic bar code that stretches all the way back to the pond-slime from which we evolved, via every evolutionary step on the way. The closer the relationship between two people, the more similar their DNA will be and it is possible to derive an indication of Time to Most Recent Common Ancestor (TMRCA) by comparing the two test results. DNA changes over time, because of accumulated mutations. However, people who are closely related or belong to the same ethnic group and/or are from the same original locality, will be more similar to each other. Put simply: the more similar the DNA, the closer the relationship. Therefore, it is possible to identify closely related people who live far apart – Scotland, America and Australia, for example.

DIFFERENT TESTS

1. The Y-test.

One of the 23 pairs of human chromosomes has a specialised function – the sex chromosomes, X and Y, which largely determine gender. Females are XX, with one X contributed by each of the parents. Males are YX, and the Y can ONLY come from the father, and his father, and his father etc. In the simplest case, the Y should follow the surname back many generations and testing the Y in many individuals should determine their relatedness in the paternal line, their inter-relatedness, the make-up of branches of the name and so on. Usefully, it is possible to assign relatedness within the last 1000 years or so and thus often within the period covered by documentary evidence such as pedigrees, certificates of birth, marriage and death, along with all the other clubs in the genealogist’s bag.

Humans have some 25,000-30,000 active genes, but the Y only has 25-30, making it about 1000th of a male’s overall genetic make-up. However, it does provide a “signature” of the paternal line, hence the importance for surname and male-line inheritance.

STRs and SNPs

There are two types of test. There are short, repeated segments of DNA at various places between the actual genes on the Y-chromosome. The nature of these Short Tandem Repeats (STRs) and their number at any given place (called a locus, or marker) can be read off like a barcode. Typically, a Y-DNA test will analyse the number of STRs at 37, 67 or 111 markers, producing a string of numbers. How similar or different this pattern is gives an estimate of relatedness and the more markers tested, the more refined the answer. An STR test will also predict the haplogroup (see map) the individual belongs to.

The SNP (Single Nucleotide Polymorphism) test looks for individual changes at a number of individual markers. The “terminal” SNP is the marker for a particular haplogroup. An STR haplogroup designation like R1b1a2a1a2c is meaningful as it shows the position in the haplogroup I tree, but it can become unwieldy. Therefore it is often referred to by its SNP equivalent.

2. The Autosomal Test

The other 22 pairs of chromosomes (called ‘autosomes’) are also inherited from the parents, but recombination means there is no straight-line relationship back to all ancestors. However, testing the autosomal DNA shows two things:

a) The deep ancestral admixture peculiar to that individual.

b) Relatedness across all lines between individuals back about 7 generations (so 5th cousins and closer, within about the last 200 years) and therefore likely to be found in typical family trees.

3. Mitochondrial DNA

Separate from the cell nucleus, cells contain tiny power-generators called mitochondria, uniquely inherited from the mother, which contain their own DNA. Therefore, they can trace a line back from a man or woman through the mother, her mother, grandmother etc. This will obviously not follow a single surname, but can be used to link an individual to a known maternal line or ancestral ethnic origin – as applied recently to the remains of King Richard III.

WHICH TESTING COMPANY?

Being told “Your male ancestors were Gael/Norse/British/Chinese” is a lot less satisfying than “You match the Y-STR signature of [however many] others with your surname and you fall into a certain subgroup, so go and compare family trees with them”. Clearly it is best to test with a company that offers both types of test and has a large database within which to find matching tested individuals. At present, only Family Tree DNA (www.ftdna.com) provides these. Test results from companies which offer only SNP tests cannot help much with genealogical research, but this will change as more Y-SNPs are added to the panel of tested markers. Family Tree DNA offers “The BigY”, which tests across about 12 million bases in the male-specific region of the Y-chromosome (MSY) and other companies have similar offerings. The STR remains the starting point for serious genealogical investigations.

IS MY DNA SCOTTISH, IRISH, NORMAN, ETC?

There is considerable doubt about what actually constitutes 'Norman', Flemish or 'Viking' DNA as these were not homogeneous ethnic groups. ‘Celtic’ was a culture, not an ethnicity. The Scots are made up of Celts, Picts, Britons, Gaels, Norse, Irish, Anglo-Dane and other incursions. These incomers were themselves made up of a wide range of unconnected genetic lineages.

What DNA testing can do, if enough of the right people have tested and the right level of tests are taken, is identify the geographical prevalence of one line amongst people alive today. That may be different from those who lived in the same places a thousand or more years ago. For a few lineages which have solid and documented pedigrees back to 1200/1300 or so, then the genealogical data may corroborate the DNA evidence and vice-versa. However, more than in many countries, the different ethnic groups which made up the Scottish population have stayed highly represented where they first arrived – especially in relatively isolated places with settled populations such as Orkney.

THE FUTURE

DNA testing is here to stay and can only get more refined, cheaper and widespread. This runs alongside the increasing accessibility of relevant documents and traditional family trees. Bringing these together is the new holy grail of genealogy. If it produces uncomfortable results… well, that’s also a charge laid against the ready availability of vital records. The genie cannot be re-bottled!

Dr. Bruce Durie is Shennachie to the Chief of Durie, Honorary Fellow at the University of Strathclyde and Member of the Académie Internationale de Généalogie Email: gen@brucedurie.co.uk Website: www.brucedurie.co.uk