Any site (locus) in the genome of an organism at which the DNA base sequence varies among the different individuals of a population. Such markers generally have no apparent effect on the phenotype of the individual, but they can be determined by biochemical analysis of the DNA and are used for a variety of purposes, including chromosome mapping, DNA profiling, and genetic screening. Genetic tools such as restriction enzymes and the polymerase chain reaction plus the ever-growing abundance of DNA sequence data, coupled with automated high-throughput assays, have revealed several classes of molecular markers, including restriction fragment length polymorphisms (RFLPs), variable number tandem repeats (VNTRs), short tandem repeats, microsatellite DNA, and single nucleotide polymorphisms (SNPs).