Abstract
Effects of temperature during embryonic development upon the manifestation of multistar marking, which appears on the larval integument of the silkworm, were studied using five strains showing different phenotypes. Two kinds of multistar marking controlled by the non-allelic genes, ms-i and ms-d, are discriminated by the effectiveness of low temperature, the manifestation of the phenotype on the 10th segment and the result of breeding experiments. One, ms-i, increases the expressivity at low temperature (15°C) and lacks the star marking on the 10th segment, while the other, ms-d decreases the expressivity and produces the marking on the 10th segment. Temperature is effective for both multistar markings during early embryonic blastokinesis, at which time the dorsal integument of the abdominal segment as well as the anlage of this marking differentiates. Different responses to low temperature in the two genes seem to depend upon the time of gene action; the ms-d gene acts earlier than ms-i. The expressivity of both multistarts was also increased by incubation at 35°C for one day; at this temperature the activity of the suppressors regulating the expressivity of this marking might be inactivated.
