Microsatellites in the silkworm, Bombyx mori:: Abundance, polymorphism, and strain characterization

We have isolated and characterized microsatellites (simple sequence repeat (SSR) loci) from the silkworm genome. The screening of a partial genomic library by the conventional hybridization method led to the isolation of 28 microsatellites harbouring clones. The abundance of (CA)(n) repeats in the silkworm genome was akin to those reported in the other organisms such as honey bee, pig, and human, but the (CT)(n) repeat motif is less common compared to bumble bee and honey bee genomes. Detailed analysis of 13 diverse silkworm strains with a representative of 15 microsatellite loci revealed a number of alleles ranging from 3 to 17 with heterozygosity values of 0.66-0.90. Along with strain-specific microsatellite markers, diapause and non-diapause strain-specific alleles were also identified. The repeat length did not show any relationship with the degree of polymorphism in the present study. The co-dominant inheritance of microsatellite markers was demonstrated in F-1 offspring. A list of primer sequences that tag each locus is provided. The availability of microsatellite markers can be expected to enhance the power and resolution of genome analysis in silkworm.