Induction of zzzw sex chromosome type tetraploid strain by treatment with hot water of inseminated eggs laid by triploid female moths in the silkworm bombyx mori

Hirokawa, M.

When the inseminated eggs from the female carrying the black egg color, normal blood and sex-limited sable marking genotype (pe, +/+, re, p, + Y/, + Y, ZW psa) crossed with the male carrying the pink egg, yellow blood and plain marking genotype (e, re/pe, re, p Y/p, Y, ZZ) were treated immediately after oviposition with hot-water at 46.degree. C for 18min., 42.9% of the treated eggs hatched out. The sex ratio of female: male was 158 : 3 and 154 out of 158 females characterised by pale sable marking, yellow blood and black eyes were triploid. The inseminated eggs from triploid females crossed with diploid males were subjected to the same treatment as that mentioned above. Hatchability of the treated eggs was 22.5% and the sex ratio of female: male was 133: 4. All the females expressed the black eye, yellow blood and pale sable marking character and segregation of egg color, blood color or marking was not recognized. The chromosome number of the embryos in the treated eggs and oogonia of female larvae hatched was tetraploid (4n = 112). Furthermore 7 females were crossed with diploid males carrying the sex-linked recissive oily skin gene; os/os and 40.9% of these eggs hatched out. No oily skin larvae were detected and the sex ratio of female: male was 170: 209, almost 1: 1. Based on these results, it was confirmed that the reduction division in the triploid egg nucleus was inhibited by the hot-water treatment and the resultant ameiotic triploid egg nucleus (ZZW) fused with the haploid sperm pronucleus (Z), leading to the formation of ZZZW sex-chromosome type tetraploid female zygote.