SSR based linkage and mapping analysis of C, a yellow cocoon gene in the silkworm, Bombyx mori

The yellow color of the cocoon of the silkworm Bombyx mori is controlled by three genes, Y(Yellow haemolymph), I (Yellow inhibitor) and C (Outer-layer yellow cocoon), which are located on linkage groups 2, 9 and 12, respectively. Taking advantage of a lack of crossing over in females, reciprocal backcrossed F-1 (BC1) progeny were used for linkage analysis and mapping of the C gene using silkworm strains C 108 and KY, which spin white and yellow cocoons, respectively. DNA was extracted from individual pupae and analyzed for simple sequence repeat (SSR) markers. The C gene was found to be linked to seven SSR markers. All the yellow cocoon individuals from a female heterozygous backcross (BC1F) showed a heterozygous profile for SSR markers on linkage group 12, whereas individuals with light yellow cocoons showed the homozygous profile of the strain C108. Using a reciprocal heterozygous male backcross (BC1M), we constructed a linkage map of 36.4 cM with the C gene located at the distal end, and the closest SSR marker at a distance of 13.9 cM.