Induction of sex-limited cocoon color character by translocation of yellow blood gene Y(Ⅱ-25.6) onto W chromosome by γ-irradiation in silkworm, bombyx mori

Sex discrimination is an indispensable and labor-demanding process for production of hybrid eggs in the silkworm Bombyx mori L. Cocoon color character can be effectively applied for sexing if the yellow blood gene Y(Ⅱ-25.6) be artificially translocated onto W chromosome to result in sex-limited trait. A total of 8,618 RF₂ batches had been screened for W-translocation type during the 7-year period of 1982 through 1988. Sex-linked oily gene(Zod) had been used for early screening of female larvae in the RF₂ generation. A single egg-laying of translocation type had been identified from 4th-day female pupae under 6 Krad irradiation in 1988. The frequeneies of the unexpected individuals in both sexes were 7.6% in RF₂ and 6.3±2.4% in RF₃, the variation of which reflects the unstable nature of the translocated chromosome fragment in each genetic background. If the translocation be stabilized through genetic manipulation, parent inbreds be identified for superior hybrids and other economic characters be improved, the translocation type can be utilized for sex discrimination (yellow cocoon for female and white for male) of the inbred to save sexing labor for hybrid egg production.