Evolution of the dec-1 eggshell locus in Drosophila. II. Intraspecific DNA sequence analysis reveals length mutations in a repetitive region in D. melanogaster.

The dec-1 eggshell gene in Drosophila melanogaster encodes follicle cell proteins required for proper eggshell assembly. As shown by Southern 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 in the numbers of the first five repeats. The results suggest that the alleles have been generated by unequal intragenic crossing-over and/or slippage during DNA replication and that the allelic length variants have arisen independently. The possibility that the most common allele, FC1, has a selective advantage over the other alleles is discussed.