Identification and genetic mapping of RAPD markers linked to the densonucleosis refractoriness gene, nsd-2, in the silkworm, Bombyx mori

In the silkworm, Bombyx mori, nonsusceptibility to B. mori densonucleosis v irus type-a (BmDNV-2) is controlled by a recessive gene, nsd-2 (nonsuscepti bility to DNV-2). We investigated the genetic linkage between two random-am plified polymorphic DNA (RAPD) markers and the +(nsd-2) gene. Initially, we constructed the JSD-2 strain (nsd-2/+), which is congenic to strain J137 ( nsd-2/nsd-2) with respect to the chromosome containing the +(nsd-2) gene, s tarting with a female of strain J137 and a male of strain C137 (+(nsd-2)/+( nsd-2)). Genomic DNAs were compared between infected individuals of the JSD -2 strain and J137 by a polymerase chain reaction (PCR) with 700 arbitrary 10-mer primers. Two RAPD markers (OPH19R and OPP01R) linked to the +(nsd-2) gene were found. For the crossing-over experiment, a female of J137 was cr ossed with a male (nsd-2/+) of JSD-2. Segregation analysis showed that the most closely linked RAPD marker (OPP01R) was mapped 4.7 cM distant from +(n sd-2).