Preferential Pairing of Sex Chromosomes in the Tetraploid Silkworms (Bombyx Mori)

摘要

In the oocytes of the silkworm, Bombyx mori, only the sex chromosome bivalent (ZW) can be identified among the 28 bivalents, when we use the females of the sex-limited yellow cocoon (Sy) strain, in which the W carries a long fragment of the second chromosome. Autotetraploid silkwonns were induced from Sy females, in order to investigate whether preferential pairing between Z and Z as well as W and W occurs in the 4n oocytes. Two types of pairing patterns, (ZZ + WW) and (ZW +ZW), were observed in the oocytes, and the ratio of the pairing patterns, (ZZ+WW): (ZW + ZW), was 34:21 in Sy4n (Sy♂× Sy♀), while 16:2 in Syr4n (Sy♂× re9♀). Sex chromosome formulae of the eggs formed by the tetraploid can he confirmed when tetraploid females are crossed with sch males (sex-linked chocolate larva). The triploid off spring from Syr4n females mated with sch males, showed ZW gametes and ZZ gemetes produced in a 22:l ratio, which coincides with the ratio calculated from the pairing pattern ratio, 16:2. The results indicated preferential pairing of Z with Z and of W with W in tetraploid oocytes.