Relation between lethality of <i>H</i>-and <i>Kp</i>-recombinants (<i>E</i>-pseudoallelic group) and environmental conditions in silkworm

Abstract

Recombination analysis between H and Kp, two genes of the E-pseudoallelic gene group has been reported in another paper.2) The present paper deals with the relationship of the lethality of the recombinants to environmental conditions.The hatching ability of the eggs of genotype HKp/++ incubated under favorable conditions, for example at a temperature of 23-25°C and 75-80% humidity in the incubation room are shown in Tables 1-2. The mean hatching rate was 79.0% in the cross +×HKp/++ and 83.6% in the reciprocal cross. According to the survey of the hatched larvae the number of the HKp heterozygotes is less than that of normal larvae. In both crosses, +×HKp/++ and HKp/++×+, normal and HKp heterozygous larvae segregated in the ratio 1.5:1.On the contrary, under less favorable conditions, for example at a high temperature of 27-28°C and low humidity of 50-60% in the thermostat, the same eggs showed a low hatching ability as shown in Tables 3-4, i. e. the mean hatching rate was 58.2% in the cross +×HKp/++ and 51.5% in the reciprocal.The phenotypic segregation of the hatched larvae is represented in Tables 5-6. In the segregation of both crosses, +×HKp/++ and HKp/++×+, the number of larvae heterozygous for HKp is too small in proportion to the normals. Normal and heterozygous larvae segregated in the ratio 2.9:1 in the former and 7.4:1 in the latter cross.Theoretically speaking, when the normals are backcrossed to the heterozygotes the two types of larvae should be segregated in the ratio 1:1. The fact that the heterozygous larvae are always fewer than the normals can be explained by the lethal action of the genetic constitution HKp/++ which affects the embryonal stage. We can find many dead eggs produced in each of the batches of Tables 1-4. Probably a major part of the individuals found dead within the eggs may be regarded as HKp heterozygotes. It is clear from the results mentioned above that this lethal action affects the larvae more severely under unfavorable than favorable conditions.However, some batches showed an abnormal segregation in which the number of the larvae of genotype HKp/++ was by far smaller than that of the normals, even if the individuals within all dead eggs were regarded as HKp heterozygotes. Studies on the cause of this abnormal segregation are now under way.