Abstract: 【Aim】 The hybrid offspring of an alive female silkworm, Bombyx mori “Qiufeng× Baiyu” brought back to the earth after travelling onboard Tiangong-2 space laboratory in space for 33 d in 2016 was mated with the male moth of “Baiyu” strain reared on the earth ’s surface for producing eggs. Small cocoon individuals were found from the offspring, and then the normal cocoon strain TG and small cocoon mutant strain sc of ‘space silkworm’ were isolated and established. The objective of this study is to reveal the gene that leads to this mutant by analyzing its inherited characters and mapping the mutant gene. 【Methods】 Phenotypic analysis of TG and sc was performed. The sc, TG and normal large cocoon strain 0223V1 were served as experimental materials for preparation of (sc♀×0223V1♂) F₁ and its backcross types, (sc♀×0223V1♂) F₁♀×sc♂ and sc♀×(sc♀×0223V1♂) F₁♂, which were designated as BC1F and BC₁M, respectively. To screen polymorphic SSR markers, the genomic DNAs of sc, 0223V1 and F₁ were used as templates, and 10 SSR primers were randomly selected from each linkage group of B. mori for PCR amplification. By utilizing the characteristic of non-crossing-over between chromosomes in female B. mori, BC₁F population was used to identify the linkage group of sc gene. According to the SSR linkage map of B. mori, BC₁M population was used for gene mapping. 【Results】 Phenotypic analysis showed that the body size of sc larvae was smaller than that of TG larvae, and the cocoon weight of sc was about half that of TG. Genetic analysis showed that the mutant was controlled by a pair of recessive gene sc. Gene mapping results showed that sc is located between S2930-363 and S2930-289 SSR markers in the 3rd linkage group of the B. mori genome, with a physical distance of 684 kb containing 33 candidate genes. 【Conclusion】 This small cocoon mutant of space silkworm is controlled by a pair of recessive gene named sc located in the 3rd linkage group of the B. mori genome.

Key words: Bombyx mori, space mutagenesis, small cocoon, SSR markers, gene mapping