Locus

Locus is a term used in genetics to describe the physical location of a gene or mutation on a chromosome. A variant of the similar DNA sequence located at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map. Gene mapping is the process of determining the locus for a particular biological trait.

Definition

In genetics, a locus (plural loci) is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. Each chromosome carries many genes, with each gene occupying a different position or locus; in humans, the total number of protein-coding genes in a complete haploid set of 23 chromosomes is estimated at 20,000 to 25,000.

Alleles

An allele is a variant form of a gene. Some genes have a variety of different forms, which are located at the same position, or genetic locus, on a chromosome. Humans are called diploid organisms because they have two alleles at each genetic locus, with one allele inherited from each parent.

Genetic Map

A genetic map is an ordered list of the genetic loci along a chromosome. The distance between the genes is measured in centimorgans (cM). This is a unit of recombinant frequency which is used in the construction of genetic maps.

Gene Mapping

Gene mapping describes the methods used to identify the locus of a gene and the distances between genes. There are two gene mapping strategies: linkage mapping and physical mapping.

See Also

• Genome
• Genetic linkage
• Genetic marker
• Centimorgan
• Recombinant frequency