A locus, as related to genomics, is a physical site or location within a genome (such as a gene or another DNA segment of interest), somewhat like a street address. The plural of locus is loci.
Locus. Locus is a term that we use to tell us where on a chromosome a specific gene is. So it's really the physical location of a gene on a chromosome. It's a way of defining the gene's neighborhood. If you consider the entire chromosome as a country where the gene is found, and then a region of the chromosome would be the city. The more specific area, or the locus, is this particular neighborhood where the gene is found.
Chief & Senior Investigator
Medical Genetics Branch