Study on Inheritance and Transgressions at Cocoon and Shell Weight Characters between Genetically Sex-limited Silkworm Bombyx mori L. Lines

Abstract

Inheritance of cocoon and shell weight characters in silkworm crosses between sex-limited at larva stage lines, including three (NIG1 × TV3/2, NIG1 × TBV2/24 and NIG1 × B2/6) from Japanese type and three (NIG2 × B2/6, TV3/2 × NIG1 and NIG2 × TBV2/24) from Chinese type was studied at Regional Centre for Scientific-Applied Service - Vratza during the period of 2000 -2002. Inheritance of tested characters in F1 was determined through genetic parameters, additiveness (a),dominance (d) and their ratio (d/a). Degree and frequency of transgressions in F2 were calculated also. Over dominance (d/a > 1) with bigger contribution of the parent with higher value was determined at inheritance tested characters. Transgressions obtained at cocoon and shell weight characters were positive and varied in wide limits. The productivity of parent’s lines had defined the variability of genetic parameters for degree and frequency of transgressions. Combination of positive transgressions at cocoon and shell weight characters in F2 hybrid populations from sex-limited at larva stage allow us to select individuals with high productive potential for further use in selection programs.