Locus (genetics)

The locus (lat: "place", plural: loci ) or gene locus ( locus ) is the physical location of a gene in the genome. The genome consists of several chromosomes, the locus of the location on the chromosome to which the gene is located. Different forms or variants of this gene are called alleles, all of which are located in the same place on the chromosome, namely the locus. The term originated in the creation of the first genetic maps and is linked to the realization that genes have a certain arrangement on the chromosomes.

To name the locus you are first, the number of the chromosome, then one of the letters for the arm with respect to the centromere, either p ( from French petit ) for the shorter or q ( simply drop the following letter) for the longer, and finally numbers for the region, the belt and the lower belt on the chromosome, the latter is separated by a dot. In the first drawing the locus 22q12.2 is highlighted in red. This nomenclature is no reference to the function of the gene, as one, for example in terms such as Hox gene MYH9 or encounters, but merely describes the place. So one can say that MYH9 in humans is the gene locus 22q11.2. Another example of this notation is the disease 1q21.1 - deletion syndrome, which is caused by partial deletion of the gene locus 1q21.1.