The effect of translocated second-chromosome fragments on sex chromosome pairings in ZZWW tetraploid female silkworm, Bombyx mori

Tanaka, N.; Yokoyama, T.; Ninagi, O.; Abe, H.; Oshiki, T.

To investigate the effect of the second-chromosome fragment, which is translocated on the W chromosome, on the behavior of sex chromosomes in the meiosis of tetraploid female silkworms, we induced two types of ZZWW tetraploid female silkworms through cold treatment of the eggs. The two types of the ZZWW tetraploid female silkworm, which were congenic for W chromosomes, were ZZWW and ZZT(W;2)Y T(W;2)Y. The frequency of males in the filial triploids produced by the tetraploid females was only 5.9%. These females had W chromosomes from a sex-limited yellow blood strain for T(W;2)Y, in which the second chromosome fragment is translocated on the W chromosome (ZZT(W;2)Y T(W;2)Y). This shows a clear difference from 21.9%, which was obtained in the case of tetraploids having normal W chromosomes (ZZWW). These results suggest that in the meiosis of the ZZWW tetraploid female, the frequencies of pairing between T(W;2)Y chromosomes are higher than those of normal W chromosomes because of the increased affinity of the translocated second-chromosome fragments.