Recombinant DNA technology and modern molecular biology allow information about an individual’s genotype to be defined at the molecular level. Two types of variation are present in DNA: sequence variation and length variation. At a given locus, variations in nucleotide sequence create different alleles, and different phenotypes. These variations can also create or destroy restriction enzyme cutting sites, producing heritable differences in the size of restriction fragments. These variations are called restriction fragment length polymorphisms (RLFPs). Many genomes also contain clusters of repeated nucleotide sequences called minisatellites. Each repeat can contain between 10-100 nucleotides, and the number of repeats at each locus can vary from 2 to more than 100. These variable variations in length are called variable number tandem repeats (VNTRs), and each variation is an allele. These differences in the number of sequence repeats between individuals can be visualized to determine the genetic identity of a DNA sample, producing what is called a DNA fingerprint.
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