Additional evidence of the formation of unbalanced embryos in cattle with the 7/21 Robertsonian translocation.
To confirm the effect of the 7 21 Robertsonian translocation on fertility in Japanese Black Cattle, cytogenetic studies were performed on embryos collected from the following 3 mating groups: normal bull cross normal cow, translocation carrier bull cross normal cow, and normal bull cross translocation carrier cow. All the analyzable embryos showed normal chromosome complements when the parents had a normal karyotype. In the group sired by the 7 21 translocation heterozygous bulls, a total of 56 embryos had metaphases suitable for chromosome analyses. Out of these embryos, 28 had normal chromosome complements and 25 were embryos with a balanced karyotype. However, 3 (5.4%) were monosomic and trisomic embryos, presumably resulting from the fertilization of normal ova by aneuploid spermatozoa. Unbalanced embryos were also observed in the chromosome analyses of embryos derived from the 7 21 translocation heterozygous cows. These results suggest that the 7 21 translocation in the heterozygous state may be associated with a slight reduction in reproductive efficiency.
Hanada
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Department of Animal Breeding and Genetics, National Institute of Animal Industry, Tsukuba Norinkenkyu Danchi, Ibaraki 305, Japan.
Geshi
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Suzuki
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