To confirm the effect of the 7/21 Robertsonian translocation on fertility in Japanese Black Cattle, semen characteristics of the carrier bulls were analyzed. Further cytogenetic studies were carried out on spermatozoa and embryos derived from bulls heterozygous for the 7/21 translocation. The 7/21 translocation seemed to cause no adverse effects on semen characteristics and the fertilization in in-vitro culture system. In bulls heterozygous for the 7/21 translocation, however, unbalanced spermatozoa resulting from adjacent meiotic segregation were detected but only at a rate of 4.1%. A few unbalanced embryos, due to the 7/21 translocation, were also observed in the chromosome analysis of the embryos derived from 7/21 translocation heterozygous carriers. These results indicate that the 7/21 Robertsonian translocation in a heterozygous state brings about only a slight reduction in reproductive efficiency. In Japanese Black Catde, the 7/21 translocation appeared to be under little or no negative selection due to the slight disadvantage in reproduction.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 27: Reproduction; fish breeding; genetics and the environment; genetics in agricultural systems; disease resistance; animal welf, , 75–78, 1998
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