Translocation of Dark Purple Serosa Color Gene (w₂⁺, 10-16.1) to Sex Chromosome W to Induce Sex-limited Egg Color Trait in Silkworm, Bombyx mori L.

Male silkworm:. produce more silk than the female for the same amount of mulberry-leaf consumption. Although sex discrimination at the larval stage has been successful, discrimination at the egg stage is most economical for the male silkworm rearing. For the induction of female sex-limited egg character, the wild type black egg color gene (dark purple serosa color; w₂⁺, 10-16.1) had been translocated to the sex chromosome W by the γ-irradiation (131.6R/min, 7896R) at the middle stage of heterozygous female pupae (w₂⁺ w₂). Through a series of test-crosses to the homozygous white egg male (ZZ, w₂w₂), a translocation type of sex-limited egg color had been identified among black female eggs from 1,423 RBC₁ egg batches. The sex-limited egg character will be utilized to breed commercial varieties with improved practical characters for male silkworm rearing, along with experiments to minimize the duplicated segment in the gerome and to stabilize the translocated portion onto the W chromosome. Also a proposal was presented for the measurement of degree of stability of the translocation; Stability Index (SI). SI value in the study was estimated to be 89.1%.