Alleles of the fibroin gene coding for proteins of different lengths.

Bombyx mori silkworms producing fibroin proteins of different lengths have been analyzed genetically and shown to possess variant alleles of a single fibroin gene. The structures of two alleles have been compared by using restriction endonuclease sites inside and outsite the fibroin gene as physical markers. We find that fibroins distinguishable on the basis of length are encoded by genes with different internal structures and overall lengths. Our results strongly support the idea that rearrangements within the highly repetitive sequences of the fibroin gene are the result of unequal recombination, and can give rise to variant fibroin genes with altered coding lengths.