| Study and application of polyploid in the silkworm is one of leading important research fields in genetic analysis, exploitation of breeding material, breeding and biological control, which can be related to many other research areas. Although many delighting achievements had been acquired by the continuous hard working of former researchers, there still exists a lot of problems that needs further studing. Based on this, we carried out this studing, and the results were described as follows:1 Polyploid can be induced by microwave treatment in the eggs of hybrid silkworm, and the induced ones were identified by their difference in the size of the egg, shape of the egg, chromosome and Sex-chromatin body(SB) numbers of the cell. Here, I introduce a new method to induce polypoid in silkworm , Bombyx mori, which was established by myself.2 Tetraploid can be induced by the method of super-cooling in silkworm . Different, factors such as stage of embryo after egg laying, temperature, super-cooling times and preservation temperature after super-cooling treatment determine the rate of polyploid induction. In our study, we had designed different levels for each factor, and found that the combination of 150 minutes after egg laying, treated at -10癈, for 24 hours and preservation at 17-19癈 is the optimizedcondition for polyploid induction.3 In this paper, we discussed the effect of the super-cooling treatment at different embryo stages based on their rate of tetraploid induction and the sex ratio of triploid in the next generation. In all hybrids, the tetraploid ratio of the female silkworm was determined by the number of embryo which are at their first cleavage period. If the number of embryo at the first cleavage period is more, the rate of tetraploid induction also be higher. In this paper we discussed the reasons for the change in sex ratio from 3 female : 1 male to 5 female : 1 male from the triploid female silkworm which is generated from a tetraploid female silkworm. This may be due to the active mechanism involved during meiosis of tetreploid parent chromosomes. In triloids, the selective synapsis is found to occur within Z and Z chromosomes, W and W chromosomes firstly, and hence the sex ratio here is 3 female : 1 male. With the increase in selective synapsis, the frequency of free synapsis between Z and W chromosome also will increase, resulting in the sex ratio of 5 female: 1 male.4 Based on the SB numbers of the female adult, the characters of eggs laid, the separate ratio of marker gene, sex, and body color of newly hatched larvae, we obtained silkworms of 3A + ZZWW type from the next generation of the induced ZZWW tetraploids. Depending on the characters of abnormal eggs laid by ZZWW triploids , we overrule the hypothesis laid by previouse researcher that the quantitive Egg determining gene (Esd) determining the egg size on the W chromosome. 5 From our finding that the triploids types like 3A+ZZ, ZZW, ZWW and 3A+ZZWW are generated from the cross between induced ZZWW tetraploid type and ZZ diploid type, we can conclude that there are free synapsis andselect synapsis during raeiosis in the female silkworm simultaneously. The results of our experiments is supplementary with the previous studies already reported. Due to the interference of W chromosome transposition, impregnation and other factors during the procreation, the ratio of ZWW type is found to be very low in our exprements. The ratio of Z-Z-ZWW-ZWW synapsis separate model is lower than other synapsis separate models in our study and this may be the reason for having a lower rate of ZZZ type in male and ZZWW type in female than the rate of ZZW type in male silkworm .6 The eggs of female formed from the cross betweem ZW and ZZ, when subjected to hot water treatment seems to enlarge some eggs' size, these big eggs when crossed with ZZ , they produced a progeny with some ZZZZWW hexaploid. These above facts proved that stimulation at embryo stage could cause the chromosome to double or no-meiosis.7 We had also inves...
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