The United Kingdom – the first country to have a detailed map of the genetic distribution of its people

The United Kingdom boasts a colourful history of wars, invasions, and both immigration and emigration of many, many different people. Archaelogists and historians can tell us much about how the Romans, Vikings, Normans and many others impacted the lives of the native Britons who lived here – but how are these historical events reflected in the genetic makeup of the population? Did these conquerors leave a lasting impact on the DNA of the people of the British Isles? Twenty years ago, Sir Walter Bodmer (a group leader at the WIMM) initiated a colossal study to collect DNA from thousands of individuals in the UK to address this very question, and the findings were finally published last month in Nature. Katarzyna Hutnik, a scientist in Sir Bodmer’s lab who was involved in the study, explains more.

“The Nature paper describes a way to read the book of history in human DNA to a level of detail that is completely unprecedented. In fact, the new technique is the closest thing we have to a time machine.”

Christine Kenneally, journalist and novelist

In 1994, Sir Walter Bodmer was asked by the BBC Horizon team to present a program on how genetics can be used to help uncover the history of the United Kingdom, answering long-standing questions about how the ancestry of modern day inhabitants of the UK has been affected by the invasion of many different groups of people over centuries of history.

Genetics refers to the study of DNA, which carries all the information required to build a human being. Your unique DNA sequence is a combination of information from your mother and father, and therefore is directly impacted by the ancestry of your parents – e.g. which country they came from. DNA could therefore potentially be used to trace back the history of an individual and their ancestry over hundreds and hundreds of years – which is what Sir Walter Bodmer and Peter Donnelly of the Wellcome Trust Centre for Human Genetics set out to do when they began to collect samples in 2004, and the ‘People of the British Isles’ (PoBI) project was born.

We collected a total of 2039 samples from rural areas of the British Isles; from people whose four grandparents were all born within 80km (50 miles) of each other. After over a decade of sample collection and data analysis, the findings of the study were published in Nature in March this year.

We were absolutely astonished to obtain 17 clusters of individuals based solely on similarities in their DNA that matched remarkably well their geographical locations.

The map shown in Figure 1 is a plot of all the individuals at the average position of their grandparents’ place of birth, where different groups are represented by the combination of the type of symbol and its colour.

The most striking observation is the extraordinary correspondence between the genetic clusters and geographical location.

For each individual, the coloured symbol representing the genetic cluster to which an individual is assigned is plotted at the mean position of their grandparents’ birthplaces. Cluster names are in the side bar. Contains OS data © Crown copyright and database right 2012. © EuroGeographics for some administrative boundaries.

By successively merging the most similar clusters one can obtain a hierarchical cluster tree as shown in the upper right hand part of Figure 1. Here, the groups that are most similar have the shortest branches between them, as for example the three clusters in Orkney (purple squares, green circles and orange crosses), and the two in South Wales (pink squares and inverted yellow triangles).

Interestingly, based on this hierarchical clustering, north and south Wales are about as distinct genetically from each other as are central and southern England from northern England and Scotland, and the genetic differences between Cornwall and Devon are comparable to or greater than those between northern English and Scottish samples.

The most different of all the clusters from the rest of the UK are those found in Orkney, which clearly corresponds to the existence of a Norse Viking Earldom in Orkney from 875 to 1472.

The next level of separation shows that Wales forms a distinct genetic group, followed by a further division between north and south Wales. This division corresponds well with the ancient kingdoms of Gwynedd (independent from the end of the Roman period to the 13^th century) in the north and Dyfed in the south.

Subsequently, the north of England, Scotland, and Northern Ireland collectively separate from southern England. Then, at the next level, Cornwall forms a separate cluster quite distinct from Devon, followed by Scotland and Northern Ireland separating from northern England.

The split in the Northern Ireland group, one with the Scottish highlands and the other with the lowlands, suggests association with the people of Dalriada and with the Picts, respectively, a separation of clans that existed around 600 AD. The split in south Wales (pink squares and yellow inverted triangles) is suggestive of “Little England beyond Wales”.

Particularly striking is the distribution of the large cluster of people (red squares) that covers most of eastern, central and southern England and extends up the east coast. This cluster contains almost half the individuals analysed (1006).

Several of the other genetic clusters show similar locations to the tribal groupings and kingdoms around at the time of the Saxon invasion (from the 5^th century), suggesting that these tribes and kingdoms may have maintained a regional identity for many centuries. For example the Cumbrian cluster corresponds well to the kingdom of Rheged, West Yorkshire to the Elmet and Northumbria to the Bernicia (see Figure 2 in the most recent newsletter on our website, link below).

The existence of these largely quite well separated clusters suggests a remarkable stability of the British people over quite long periods of time. This is in marked contrast to what is often assumed.

To understand the relationships of the clusters to each other we need to consider the history of the British people and the possible contributions to their genetic makeup from the surrounding European countries.

It is important to emphasize that, although the genetic clustering found by our analysis is based on very small genetic differences, we think it nevertheless represents a major step forward in the genetic analysis of human populations.

For more information, please see the ‘People of the British Isles’ website here.

You can also watch a short film by the Wellcome Trust on the PoBI project here: