From the Belgian Blue to the Brown Swiss and the Tibetan yak...
Some animals from the Brown Swiss breed also have the “lineback” phenotype. “We discovered that researchers from the University of Bern were working on the genetics of this breed’s coat and we contacted them so that we could collaborate with them. We wanted to check whether this phenotype resulted from the same genetic mechanism in the Brown Swiss”, Carole Charlier explains. Initially, this didn’t seem to be the case: “The analyses they had already initiated had allowed them to locate the region of the genome responsible for this phenotype in chromosome 6, in a region close to the KIT gene”, the scientist specifies. At first sight, these results were therefore incompatible with those found for the Belgian Blue.
But it would have taken a lot more to discourage the group of researchers from Liége! Once they had the Brown Swiss DNA samples in their hands, they carried out the same genetic analyses as those performed for the Belgian breed. “These analyses revealed that in the Brown Swiss, part of the duplicated piece of chromosome 6 inserted into chromosome 29 had excised and circularised itself, taking a fragment of chromosome 29, and had reinserted itself into chromosome 6 through a homologous recombination mechanism”, Carole Charlier points out (see diagram).
Eager to continue now that they were getting somewhere, the researchers extended their analyses to a wide range of cattle breeds with the “lineback” phenotype. In both European and African breeds, and even the Tibetan yak, they found the same characteristic insertion points as in the Belgian Blue and Brown Swiss. “Some breeds have the same allele as the Belgian Blue and others the same as that of the Brown Swiss, while others have both of these alleles”, Carole Charlier continues. “Hence, an original unique event occurred – the one characteristic in the Belgian Blue – that was transmitted to all cattle breeds with the “lineback” phenotype. In some of these breeds, this was followed by the second event described in the Brown Swiss. In both cases, these events help to explain this coat phenotype for the majority of the breeds we studied”.