EVOLUTION AND POPULATION BIOLOGY OF THE PERIOD GENE

The clock gene period (per), originally identified in Drosophila, evol ves relatively quickly within the insects; probably for this reason, n o convincing per homologues have been identified outside this class. H owever antibodies to Drosophila PER have labelled neural pacemakers in other organisms, including mammals. Conserved regions, such as the PA S dimerization domain, reflect its functional importance, but the long Thr-Gly repeat encoded within per is not conserved outside the Drosop hila. The repeat appears to be a component of the temperature compensa tion system in the fly. This is reflected in the population structure of natural Thr-Gly length variants of D. melanogaster. Patterns of nuc leotide variation within Drosophila per have been used to examine the selective forces that have shaped the evolution of this gene. (C) 1996 Academic Press Ltd.