A locus refers to the specific location of a gene on a chromosome. In medicine, it may also refer to the site on a body where a pathogen invades its host.
Every chromosome carries hundreds to thousands of genes, which can make it difficult for geneticists to identify particular genes. The locus serves as a guide, pointing out the physical path to a specific gene. The locus of a gene consists of three major elements: the chromosome number, the arm on which the gene is located and the position of the gene on the arm, identified by a five-digit code.
To find the gene, scientists require a powerful microscope. The locus may not always refer to a gene. It may point to a cytogenetic feature or a non-coding DNA segment. Some genes may also have several loci within them, which will require additional mapping. Being able to map the location of genes has helped geneticists identify the risk genes for certain genetic diseases. According to the National Human Genome Institute, it has also led to breakthroughs in biotechnology, with the breeding of more nutritious crops and plants that are more resistant to diseases. Gene mapping has also become a popular tool used in criminal forensics for crime investigations, paternity tests and more.