Molecular genetic characterization of Robertsonian translocations in cattle

The chromosome fusion of acrocentric chromosomes, known as Robertsonian translocations, are the most common chromosome rearrangement in Bovidae. Cytogenetic studies revealed differences between the centromeres of Robertsonian translocations: the rob(1; 29) is called monocentric, whereas rob(14; 20) is a dicentric chromosome. To analyse the type of fusion, satellite sequences were hybridised to metaphase chromosomes of carriers of rob(1; 29) from different breeds and rob(14; 20) from the Simmental breed. A repeat element of the bovine 1.715 satellite was located in the centromeric regions of all 29 bovine acrocentric chromosomes. No signals were observed on either the X-,Y- or the rob(1; 29) chromosomes. In contrast, all rob(14; 20) chromosomes gave a distinct hybridisation signal. Microsatellite markers in the linkage group, originating from the fusion, revealed a characteristic allele combination for rob(1 29) in all carriers and were able to confirm the screening of metaphases of 220 daughters of a heterozygote carrier of the rob(1; 29). The results indicate that rob(1; 29) lost parts of both centromeres and that the 1.715 satellite DNA is not necessary for the functioning of the centromere. Furthermore, rob(1; 29) appears to derive from the same mutation and is transmitted according to Mendelian law.