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Abstract: Two silkworm strains viz, B20 A (high cocoon shell ratio) and C.Nichi (low cocoon shell ratio) were sib mated for 10 generations to determine the homozygosis. Both bulked segregant analysis(BSA) and near isogenic lines (NIL) studies were done to identify the RFLP markers closely linked to cocoon shell parameters. Three hundred and fifty-two random clones were identified as the low copy number sequence and used for identification of restriction fragment length polymorphic (RFLP) marker linked to cocoon weight and cocoon shell character. In the bulk segregant analysis, DNA from the parents (B20 A, C.Nichi), F₁ and F₂ progeny of high shell ratio (HSR) and low shell ratio (LSR) were screened for hybridization with the random clones. Polymorphic banding pattern achieved through southern hybridization with different probes indicated the probable correlation of polymorphism with high and low cocoon shell character which are possible landmarks in identifying the putative marker(s) for the cocoon shell character. Out of the 100 probes tried with parents, F₁, F₂ and their bulks, 10 probes were found to be closely linked to cocoon shell characters.

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