Genetic studies on the novel lethal mutant, light orange lethal, in the silkworm, Bombyx mori

抄録

 Many lethal mutations of the silkworm egg have been reported. The lethal phenotype is exhibited at several stages including blastokinesis, head pigmentation, and body pigmentation. We recently isolated a novel lethal mutant, which the skin color of the mature embryo became a light orange and the embryo died before hatching. In this study, we performed morphological observation and genetic analysis of this lethal mutation. Phenotypic observation showed that the phenotype of this lethal mutant is quite similar to that of the sex-linked chocolate lethal (sch^l), chocolate (ch), chocolate 2 (ch-2), and maternal chocolate (cm) mutants. We first performed the crossing experiment, which revealed that this mutation is regulated by a single recessive gene, and is not linked to the sex chromosome on which the sch^l mutation is located. We next performed the pre-linkage test with this lethal mutation and three other mutations, which revealed that an allelic relationship among these mutations could not be detected. Therefore, we determined that this is a novel lethal mutant, which we named light orange lethal (l-og). We next performed the linkage analysis of the l-og mutation using 20 F₂ individuals and primer sets designed for each chromosome. The linkage analysis revealed that the l-og mutation is definitely located on chromosome 10. Furthermore, the rough mapping using 119 F₂ individuals and 7 primer sets designed for chromosome 10 revealed that the l-og-linked region was narrowed down to approximately 3.7 Mb long on chromosome 10.