A
locus (plural
loci), in
genetics, is the specific location or position of a
gene,
DNA sequence, on a
chromosome. Each chromosome carries many genes; humans' estimated '
haploid' protein coding genes are 20,000-25,000, 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.