STRs, are sometimes referred to as microsatellites or simple sequence repeats. They are brief lengths of non-coding region of the human genome. They consist of less than 400 base pairs, hence "short." STRs are 3-15 repeating units. Each of these contain 3-7 base pairs. Short tandem repeats occur on all 22 pairs of autosomal chromosomes and X and Y sex chromosomes. They vary greatly between individuals. This results from mutations, natural selection, independent chromosomal variation and recombination.
