Genetic mapping of RAPD markers linked to the densonucleosis refractoriness gene, nsd-1, in the silkworm, Bombyx mori

In the silkworm, Bombyx mori, nonsusceptibility to B. mori densonucleosis virus type-1 (BmDNV-1) is controlled by a recessive gene, nsd-l (nonsusceptibility to DNV-1), located on the twenty-first chromosome. We investigated genetic linkage between five random amplified polymorphic DNA (RAPD) markers and the +(nsd-1) gene. Initially, we constructed the CSD-1 strain (nsd-1/+) which is congenic to strain C137 (nsd-1/nsd-1) for the twenty-first chromosome, starting with a female of C137 and a male of strain J137 ((nsd-1)/+(nsd-1)). For the crossing over experiment, a female of C137 was crossed with a male (nsd-1/+) Of CSD-1. Segregation analysis showed that the most closely linked RAPD marker mapped 3.0 cM distant from +(nsd-1). A more specific marker for +(nsd-1) was made by converting this RAPD band into a sequence characterized amplified region (SCAR) using a series of newly designed primer pairs based on its DNA sequence.