<P> In the study of molecular evolution, a haplogroup is a group of similar haplotypes that share a common ancestor with a single nucleotide polymorphism (SNP) mutation . Haplogroups pertain to deep ancestral origins dating back thousands of years . </P> <P> The most commonly studied human haplogroups are Y - chromosome (Y - DNA) haplogroups and mitochondrial DNA (mtDNA) haplogroups, both of which can be used to define genetic populations . Y - DNA is passed solely along the patrilineal line, from father to son, while mtDNA is passed down the matrilineal line, from mother to both daughter and son . The Y - DNA and mtDNA may change by chance mutation at each generation . </P> <P> A variable number tandem repeat (VNTR) is the variation of length of a tandem repeat . A tandem repeat is the adjacent repetition of a short nucleotide sequence . Tandem repeats exist on many chromosomes, and their length varies between individuals . Each variant acts as an inherited allele, so they are used for personal or parental identification . Their analysis is useful in genetics and biology research, forensics, and DNA fingerprinting . </P> <P> Short tandem repeats (about 5 base pairs) are called microsatellites, while longer ones are called minisatellites . </P>

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