NIJ Training Course for Forensic DNA Officers of the Court: Genes and Loci

Genes are not contained  randomly on the chromosomes rather any particular gene can be found in a  specific location on a specific chromosome.  The gene that controls hair color for instance  is always found in the same particular location on the same particular chromosome, just as the  gene that controls right or left-handedness can always be found in its own designated location.  This location is referred to as the gene's locus and every gene has its own. There are  also some areas of the chromosomes that do not code for a physical variation in a  person such as hair color or earlobe shape. Instead, these loci contain non-coding DNA  markers as are used in forensic identity testing.