Mapping of the yellow inhibitor gene I in silkworm Bombyx mori using SSR markers

Abstract

The yellow color of silkworm (Bombyx mori) cocoon is mainly controlled by three genes, Y (yellow blood), I (yellow inhibitor) and C (out-layer yellow cocoon) genes. I gene locates on the 9th chromosome of silkworm and prevents the transport of carotenoid from epithelia of midgut into hemolymph. Owning to a lack of crossing over in females, reciprocal backcrossed F1(BC1) progenies were used for linkage analysis and mapping of the I gene based on the SSR linkage map using silkworm strains Baghdad (Ba), which express white hemolymph (II+Y+Y), and KY, which express yellow hemolymph (+I+IYY). The gene of interest was linked to three (S0904, S0905, and S0906) SSR markers. All the individuals with white hemolymph in the BC1F (BC1 was generated using F1 as female) showed heterozygous profile of (BaxKY) F1, and the yellow ones in BC1F showed the homozygous profile of the strain KY. Using a reciprocal BC1M cross, we con-structed a linkage map of 38.4 cM, and the distance between I gene and the nearest marker S0904 is 7.4 cM.