In genetics, a locus is a specific, fixed position on a chromosome where a particular gene or genetic marker is located). A gene is a heritable factor that consists of a length of DNA and influences a specific trait, and it occupies a specific position on a chromosome, which is called the locus. The locus is like a genetic street address, and it is a way of defining the genes neighborhood. Each chromosome carries many genes, with each gene occupying a different position or locus). Genes may possess multiple variants known as alleles, and an allele may also be said to reside at a particular locus). Diploid and polyploid cells whose chromosomes have the same allele at a given locus are called homozygous with respect to that locus, while those that have different alleles at a given locus are called heterozygous). The ordered list of loci known for a particular genome is called a gene map). Gene mapping is the process of determining the specific locus or loci responsible for producing a particular phenotype or biological trait).