Sequence polymorphisms around the 5′-end of the silkworm fibroin H-chain gene suggesting the occurrence of crossing-over between heteromorphic alleles

Nucleotide sequences around the 5′-ends of the silkworm fibroin H-chain genes of the three strains, Nd[2), J-139, and F₁(Gunka × Hoshun), of Bombyx mori were determined. Comparison of the sequences among these strains and the sequences reported previously for the two other strains, F₁(Gunpo × Shugyoku) and Daizo, indicates that polymorphisms are present in the 5′-flanking and intron regions and that each region has at least two sequence variants independent of each other. These results suggest that crossing over between the heteromorphic H-chain alleles has occurred during the breeding of these strains.