Characteristics of tsg, the low temperature sensitive gray-egg mutation in Bombyx mori

The low-temperature sensitive gray egg (tsg), which is a spontaneous mutation and is controlled by a single recessive gene belonging to the 5th linkage group, was characterized. This trait was expressed in a mosaic only when female pupae homozygous for tsg were subjected to a cold shock, which was most effectively conducted by chilling at 6 to 15°C at a pupal age of day 5 or 6 after the larval-pupal ecdysis. Animals thus treated deposited a mixture of normal and gray eggs; chilling for 10 hr at 10°C produced about 8 gray eggs per individual. This number corresponds to the follicle population shortly before or after the onset of choriogenesis at a given moment, indicating that this phase may be critical for the cold response. Scanning electron microscopy indicated that the lamellar structure at the middle layer of the chorion region affected by the mutation was less uniform than normal.