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The crazy tale of the Belgian Blue’s coat
3/27/12

A duplication to complicate matters

Following this work, the researchers found themselves faced with two conflicting pieces of information: the location of the gene responsible for the “lineback” phenotype in Belgian Blues on chromosome 29, and the fact that the animals with this phenotype have a duplication of the KIT gene, the gene of chromosome 6, in common.  Therefore, they had to reconcile these two pieces of information. “We thus put forward the hypothesis that the fragment of duplicated chromosome that contained this gene wasn’t duplicated in the region of origin but had inserted itself elsewhere in the genome, i.e., in the place where we had located the gene responsible for the phenotype”, Carole Charlier explains. This type of mechanism is known as duplicative translocation: instead of duplicating itself in tandem, i.e., alongside the original chromosome segment, the duplicated segment inserts itself into another chromosome. 


In order to verify this hypothesis, Keith Durkin took the analyses further by using a technique that reveals precise chromosomal segments with the help of fluorescent probes (FISH technique). “He was thus able to show that the duplicated chromosome segment containing the KIT gene had indeed inserted itself into the chromosome 29 region that we had located during the first stage of this research”,  the scientist continues. But how did this fragment of duplicated chromosome come to be there? What processes had taken place between the excision from chromosome 6 and insertion into chromosome 29? The next step for the GIGA researchers was to answer these questions. “If the piece of chromosome 6 had inserted itself into chromosome 29 in a linear manner, we would have seen the following: a piece of chromosome 29 followed by a piece of the duplicated chromosome 6 contained between two insertion points, followed by the rest of chromosome 29”, Carole Charlier describes. But this isn’t exactly what the analyses using the whole genome resequencing technique showed. The result was somewhat more complex. “In short, the segment of chromosome 6 that had inserted itself into chromosome 29 had formed a circular intermediate between these two events”, the researcher reveals. Thus, after having excised itself from chromosome 6, the duplicated segment circularised itself. And before inserting itself into chromosome 29, it then opened up again at another point, thus changing the initial order of parts composing it (see diagram).
Metaphase-chromosome

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