Genetic Structure Genetic Locus Locus, Genetic Loci, Genetic Genetic Loci MESH:D056426 SCDO:1000103 Sufficient A specific region that is mapped within a genome. Genetic loci are usually identified with a shorthand notation that indicates the chromosome number and the position of a specific band along the P or Q arm of the chromosome where they are found. For example the locus 6p21 is found within band 21 of the P-arm of CHROMOSOME 6. Many well known genetic loci are also known by common names that are associated with a genetic function or hereditary disease.