Modern DNA

The most widely used method for looking for genetic signatures of past populations is to sample from modern populations and extrapolate back to the most likely sequence of events to explain the modern genetic patterns. This method certainly has advantages. It is easy to collect samples: research groups offering genetic testing (especially where results are returned to individuals) are often overwhelmed by people willing to take part in a study. Sampling often takes the form of volunteers providing buccal (cheek) cells and can be done by sending out ‘spit-kits’ through the post. The DNA extracted from the samples is abundant, intact and straightforward to examine and it is possible to look at any section we choose—we are not limited by what DNA remains as is the case with ancient specimens. Due to their simple method of inheritance, it is the Y chromosome and mtDNA which are the most extensively studied part of the genome when examining past population histories using modern DNA.

This method is not without its own drawbacks, however. Modern samples represent the end result of all the events that have formed the population as it stands today. Questions arise as to what criteria to use when choosing who to sample to best represent the events we are interested in—sampling individuals with deep ancestry in the area is the ideal. Furthermore, researchers often wish to sample from rural rather than urban areas. As towns consistently attract immigrants from both the local surroundings and further afield, urban samples are more likely to include individuals whose ancestry is not local. Finally, few people have knowledge of where their ancestors were born, the limit often being at the grandparental level. Therefore individuals are often sampled based on parental or grandparental place of birth being within a region or with certain distance of a town giving a relatively shallow time-depth for known ancestry in the area. Such studies have concentrated on the proportion of Scandinavian ancestry in for example Iceland (Helgason, et al. 2001), the Faroe Islands (Als et al. 2006), Orkney and Shetland Islands (Goodacre, et al. 2005), the islands of the North Atlantic and the British Isles (Capelli, et al. 2003).