MOLECULAR POLYMORPHISM IN THE PERIOD GENE OF DROSOPHILA-SIMULANS

The threonine-glycine (Thr-Gly) repeat region of the period (per) gene of eight natural populations of Drosoiphila simulans from Europe and North Africa was analyzed by polymerase chain reaction, DNA sequencing and heteroduplex formation. Five different length alleles encoding 21 , 23, 25 and two different kinds of 24 Thr-Gly pairs in the uninterrup ted repeat were found. In the 3' region flanking the repeat 6 nucleoti de substitutions (3 synonymous, 3 replacement) were observed in three different combinations that we called haplotypes I, II and III. The co mplete linkage disequilibrium observed between the haplotypes and thes e length variants allowed us to infer from the repeat length, the DNA sequence at the 3' polymorphic sites. The haplotypes were homogeneousl y distributed across Europe and North Africa. The data show statistica lly significant departures from neutral expectations according to the Tajima test. The results suggest that balancing selection might have p layed a role in determining the observed levels and patterns of geneti c diversity at the per gene in D. simulans.