Mapping of the lethal genes in the sex-linkaged balanced lethal silkworm Bombyx mori using SSR markers.

The males of sex-linkaged balanced lethal silkworm strain (S-14) has two non-allelic recessive genes (lethal gene 1, l1 and lethal gene 2, l2). The two genes are located on two different Z chromosomes and cause death of embryos at body pigmentation stage and end reversal embryo stage, respectively. We firstly hybridized the males of S-14 strain with the females having wild-type genes of P50 strain and then backcrossed the males of F1 with females of P50 strain. A total of 1660 female moths of BC1 generation were divided into two groups, 1 100 in BC1-l1 and 560 in BC1-l2 according to the lethal gene carried by these female mothsfathers-fame moths of F1, respectively. Based on the nucleotide sequence information from the published physical map of Bombyx mori, we developed 16 polymorphic SSR markers in l1 gene region and 18 polymorphic SSR makers in l2 gene region compared to the allelic region of P50 strain and used these SSR markers and groups of BC1-l1 and BC1-l2 to map the two lethal genes, respectively. Gene l1 was mapped on the region of Z chromosome, covering a physical distance of 2.60 Mb. Gene l2 was fine mapped on the region of Z chromosome, covering a physical distance of 0.69 Mb.