EVOLUTION OF THE DEC-1 EGGSHELL LOCUS IN DROSOPHILA .2. INTRASPECIFICDNA-SEQUENCE ANALYSIS REVEALS LENGTH MUTATIONS IN A REPETITIVE REGIONIN DROSOPHILA-MELANOGASTER

The dec-1 eggshell gene in Drosophila melanogaster encodes follicle ce ll proteins required for proper eggshell assembly. As shown by Souther n and Northern analyses the dec-1 gene occurs in four alleles (Fc1-4) among wild-type strains. Its second exon has a distinct feature in the form of 12 repeats with 78-91 nucleotides; the first five show nearly 100% homology. DNA sequence comparison of the repeated region of the alleles revealed that the length polymorphisms are caused by changes i n the numbers of the first five repeats. The results suggest that the alleles have been generated by un-equal intragenic crossing-over and/o r slippage during DNA replication and that the allelic length variants have arisen independently. The possibility that the most common allel e, FC1, has a selective advantage over the other alleles is discussed.