Genetic characterization of silkworm (Bombyx mori L. ) strains (Lepidoptera: Bombicidae) with different geographical originon the basis of isozyme markers

The aim of the present study was to assess genetics variations within and among strains with different geographical origin, belonging to Bulgarian germplasm bank of mulberry silkworm (Bombyx moriL.)and to establish their relationships using isoenzyme markers. Polyacrilamide gel electrophoresis (PAGE) was used to study the isoenzymes of nonspecific esterases (EST), malate dehydrogenase (MDH) and acid phosphatase (ACP) from haemolymph, phosphoglucomutase (PGM) and hexokinase (HK) from silk glands and alkaline phosphatase (ALP) from midgut of mulberry silkworm (Bombyx moriL.). Variability was evident in all of these enzyme systems among twelve strains from Bulgarian germplasm resources of B. mori.Total of nine lociwere detected. All of them (100%) were polymorphic. “Null” alleles in four lociwere determined. Intra-and inter-strain polymorphism was obtained. The degree of polymorphism ranged from 0% to 77.80%. Low levels of observed heterozygosity in comparison with the expected one have been calculated in almost all of strainsas well as deviations from Hardy-Weinberg equilibrium in almost all analyzed loci, resultingof excess of homozygotes. The value of FSTwas 0.4903. The dendrogram constructed with the values of genetic distance manifests that Romanian strain Cislau Tokay is formed one main clade while the rest strains studied (from Bulgaria, Japan, China, Vietnam, Spain, Syria and Egypt) are formed the other clade withsubclades. The genetic data of the tested strains from different geographical regions, would be used for identifying suitable parents for breeding programs with a view to yield improvement in this species with economic significance.

Identification of 2nd chromosome region translocated onto the W chromosome by RFLP with EST-cDNA clones in the Gensei-kouken strains of the mulberry silkworm, Bombyx mori L

In silkworms, sex-limited strains are either obtained spontaneously or induced by X-rays or gamma rays. When a fragment of an autosome carrying a dominant allele of those genes responsible for certain characters is translocated onto a W chromosome, the female of the successive generations will express these phenotypic characters and sex discrimination can be facilitated. Gensei-kouken strains are sex-limited strains of silkworms developed by irradiating the pupae with gamma rays, by which a portion of the second chromosome is translocated onto the W chromosome. In these improved strains, the females are yellow-blooded and spin yellow cocoons. By using the EST-cDNA clones mapped on the Z chromosome, we identified the sex according to the polymorphic banding pattern or intensity of the signals. Furthermore, by using the clones on the second chromosome, the region of the second chromosome translocated onto the W chromosome was also defined. In both the A95 and A 96 strains selected for the present study, only the mid-portion of the second chromosome was translocated. The differences in length of the fragments translocated in these strains are discussed.