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Mouse embryos at morula stage were treated with various concentrations (5 to 50ng/ml) of vinblastine sulfate for 17h. A concentration of 30ng/ml was recognized to be a critical dose sufficient for the production of high incidence of metaphases. The 17-h incubation was too long, which brought about excessive contraction of chromosomes in most of the metaphases accumulated.Average lengths of no. 1 chromosomes in the embryos treated with 30ng/ml vinblastine sulfate for 8, 10 and 17h differed significantly according to the time length of vinblastine treatment.A combination of 10-h incubation and 30ng/ml vinblastine produced high average incidence of metaphases, and chromosomes were analyzable in many metaphases because of their moderate contraction. This combination was recommended for chromosome preparation of mouse embryos at morula stage.Incidences of hyperdiploid (2n+1) and triploid (3n) embryos were 0.7% and 0.5%, respectively.

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Manyinvestigators have examined the