Locus (loci in plural) is the specific, fixed location or position of a gene on a chromosome.

Genes have specific positions or locations on the chromosome referred to as a locus (loci in plural). The locus is the same on homologous chromosomes carrying a particular gene.

Key Points

• Locus is the specific position or location of genes on a chromosome and is the same location on homologous chromosomes carrying a particular gene.

Key Terms

locus: the position of a gene on a chromosome

homologous chromosomes:  chromosomes of the same length with genes in the same location; diploid organisms have pairs of homologous chromosomes, and the members of each pair come from different parents

chromosome: a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.

gene: a distinct sequence of nucleotides forming part of a chromosome coding for a phenotype