Molecular mapping of test mapping strain for 18th linkage group recessive genes elp, ch-2 and mln in silkworm (Bombyx mori)

Abstract

The ellipsoid egg, the second recessive gene of chocolate larvae, and melanism are controlled by three recessive genes, elp, ch-2, and mln in silkworm, respectively. Their order and genetic distance have been scheduled in established linkage group. Owing to lack of crossing over in females, the reciprocal backcrossed F1(BC1) progenies were bred for linkage analysis using the wild type silkworm strain P50(+elp+ch-2+mln /+elp+ch-2+mln) and W18 with ellipsoid egg, the second recessive gene of chocolate larvae, and melanism (elp ch-2 mln / elp ch-2 mln). In this research, we mapped three mutant genes, elp, ch-2, and mln on the chromosome 18 based on the SSR linkage map and STS markers designed based on silkworm genome sequence. The established linkage group, molecular linkage group, and the physic map of chromosome 18 had been corresponded. The genetic distance for this chromosome in this research was 94.2 cM, and the order of the mutants and molecular markers were consistent with the established silkworm linkage maps and the fine genome sequences. This research will lay important bases for map-based cloning for other mutants on chromosome 18.