USING CHLOROPLAST DNA TO TRACE POSTGLACIAL MIGRATION ROUTES OF OAKS INTO BRITAIN

Postglacial migration is a major factor responsible for the patterns o f genetic variation we see in natural populations. Fossil pollen data indicate that early postglacial colonists such as oak, were able to ta ke both western and eastern migration routes into Britain. Analysis at a finer level is now permitted by the use of modern molecular techniq ues. A 13-bp duplication in the chloroplast tRNA(Leu1) intron occurs i n natural populations of East Anglian oaks, but is not found in other parts of Britain or from mainland Europe. The distribution of this mar ker suggests that the mutation occurred either in southern England, or during migration from the mainland, and became fixed in a source popu lation from which East Anglia was colonized. Planting of non-native tr ees for roadside boundaries and in the grounds of old houses and estat es, explains the absence of the marker from some East Anglian oaks.