====== Locus ======

A locus (plural loci) in [[genetics]] is a fixed position on a [[chromosome]], like the position of a [[gene]] or a marker (genetic marker).

A locus is a position on a [[chromosome]] where a [[gene]] or other genetic marker is located, while an [[allele]] is a variant of a gene (i.e. a variant form of the [[DNA sequence]] located at a specific locus, coding for a specific functional product, associated with a trait)

Each chromosome carries many genes; human's estimated '[[haploid]]' protein coding genes are 19,000–20,000, on the 23 different chromosomes. 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 [[gene map]]. [[Gene mapping]] is the process of determining the locus for a particular biological trait.

[[Diploid]] and [[polyploid]] cells whose chromosomes have the same allele of a given gene at some locus are called [[homozygous]] with respect to that gene, while those that have different alleles of a given gene at a locus are called [[heterozygous]] with respect to that gene.