Analysis of sex chromosome pairings in tetraploid females of the silkworm by using the sex-linked recessive gene.

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  • 伴性劣性遺伝子を利用した４倍体雌蚕における性染色体対合の解析
  • バンセイ レッセイ イデンシ オ リヨウシタ 4バイタイ メス カイコ ニ オ

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The tetraploid female silkworms (RW4n) were induced by applying a cold shock to the eggs. Three kinds of triploids, RWsch, RWNo, and RWEq, were produced from the cross between the tetraploid females and the diploid males of three different strains characterized by a sex-linked recessive marker gene: the sex-linked chocolate (sch: sch/sch·od/od), the sex-linked translucent (No: os/os), and the elongate (Eq: e/e). The expression of the marker gene signified two kinds of the sex-chromosomal arrangement, ZZW and ZWW. Percentage of ZZW individuals for three populations, RWsch, RWNo, and RWEq, were determined as 80.20%, 80.15%, and 79.60%, respectively. The occurrence of ZZW individuals was significantly higher than the theoretically expected figure (i. e. 66.67%). This result suggested that, in the tetraploid oocytes, Z-Z and W-W pairings occurred more preferentially than the random pairing. The number of the females having ZWW chromosomes were quite low in three triploid populations. Since the ZWW females in RWsch failed to hatch spontaneously, the chorion had to be artificially removed for their survival. On the other hand, all of the ZWW females in RWNo and RWEq triploids were found among the spontaneously hatched larvae. It is suggested that the duplication of the W chromosome is not responsible for the failure. The ZWW females in the three groups consistently deposited much larger eggs than those laid by the ZZW females. The adults with ZZW chromosomes produced the normal-sized eggs mixed with many irregular ones.

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