A Robertsonian translocation and its effect upon fertility in Brown Swiss cattle.

Metaphase chromosomes derived from leukocyte cultures of peripheral blood were observed in 299 head of Brown Swiss cattle. A Robertsonian translocation (centric fusion) was found in 31 of the animals. Estimated from this small sample 2.4% of animals of the Brown Swiss breed carry the translocation. Chromosome measurements and analysis of G-banded chromosomes proved inconclusive in identification of the homologue to the short arm of the translocation chromosome. The long arm was homologous to the longest acrocentric autosome. By C-banding, a single, small area of centromeric constitutive heterochromatin on the translocation chromosome indicated a single centromere. The translocation in Brown Swiss may be homologous to the 1/29 Robertsonian translocation in many other breeds of cattle. The translocation chromosome appeared to have segregated normally from its homologues. Aneuploid karyotypes were not observed. Analyses of breeding data failed to detect any decrease in fertility of translocation heterozygous females as compared to females of the normal karyotype. It would be premature to recommend a selection program against this translocation in Brown Swiss, but widespread use of sires heterozygous for the translocation should not be encouraged.