Chapter 8 MtDNA Markers for Celtic and Germanic Language Areas in the British Isles

In this context, the term ‘marker ’ needs to be explained. Occasionally, in the course of the millen-nia, mutations may occur in the DNA of an organ-ism, such as a human or a seed of grain, and these mutations are passed down to the descendants. If these descendants remain united by a common char-acteristic such as a language, a certain geographic area, or a resistance against cereal rust, the DNA mutation can be considered a marker for that char-acteristic, even though it does not cause the charac-teristic. The two best-characterized genetic systems for identifying evolutionary markers in humans are the Y chromosome (passed down exclusively from the father to his male children) and mitochondrial DNA (transmitted exclusively from the mother to her chil-dren). Individuals living today differ genetically from each other as a consequence of different mutation events which occurred in their past ancestry, irre-spective of whether these mutation events are inter-esting markers for any characteristic. To date there have been two approaches to analyzing data for the exploration of genetic patterning: the summary method and the lineage approach. The summary method treats the entire data set in terms of a population concept which con-siders all the different genetic types as a single herit-able unit, which is passed down through time. The lineage method looks at the geographic spread and mutational age of specific lineages which in turn reflect movement of prehistoric individuals (for a discussion of the two approaches see Richards et al. 1997; Forster et al. 2001). This contrast in approach is also reflected in the choice of methods for detecting geographic patterns in genetic data. We will com-pare available coarse-grained approaches to detect-ing genetic patterns in Europe with the finer-scaled methods we propose in the main part of this paper