γ線照射によるサケのHertwig効果と雌性発生誘起

概要

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In order to determine the suitable dosage of γ-rays to induce gynogenesis in the chum salmon Oncorhynchus keta, the " hertwig effect " was investigated. Normal eggs were inseminated with milt which had been exposed to γ-rays of 60Co for doses ranging from 102 rad to 105.8 rad. The fertilization rate was not affected by irradiation even at 105 rad but fertilization did not occur at 105.8 rad. The Hertwig effect appeared in survival rate, early cleavage and embryogenesis. Most harmful doses were 103.5 ra and 104 rad at which doses no embryonic body was formed and most embryos died until 18 days after insemination although they advanced early cleavages. The irradiation beyond 104 rad recovered the survival rate and the injurious action of irradiation on the development was strikingly reduced at 105 rad. Various aneuplkodides were observed at doses from 103 rad to 104.4 rad. Paternal chromosomes were borken into fragments with increasing irradiation and gradually reduced in number. All paternal chromosomes were eliminated at the dosage of 105 rad and gynogenetic heploid embryos were induced at this dosage.
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