Linkage analysis and mapping of a gene responsible for the lethal 19 mutation in the silkworm, Bombyx mori

Abstract

In the silkworm Bombyx mori, more than ten mutations exhibit an embryonic lethal phenotype. The lethal 19 (l-19) mutation is one of these, and embryos exhibiting this mutation die at blastokinesis. The l-19 mutation is controlled by a single recessive gene mapped to chromosome 19. However, the responsible gene has not yet been identified. In this study, we performed morphological observations of the eggs and embryos using microscopy and mapped l-19. Observations revealed that eggs with the l-19 mutation die before or after the body pigmentation stage, but only embryos in eggs before the body pigmentation stage were dead at blastokinesis. This result suggests that the phenotype of the l-19 mutation can be identified by sampling dead eggs at this stage. We next performed mapping of l-19 using primer sets designed for chromosome 19. However, we could not identify the l-19-linked region, because there were no regions where the genotypes of all F2 individuals were homozygous for the l-19 mutant, suggesting that l-19 does not map to chromosome 19. Therefore, we performed a linkage analysis using primer sets designed for each chromosome. Our analysis showed that l-19 does not map to chromosome 19, but instead maps to chromosome 12. Further mapping indicated that the l-19-linked region spanned approximately 10 Mb on chromosome 12.