Hypervariable region

A hypervariable region (HVR) is a location within a sequence where polymorphisms frequently occur. It is used in two contexts: * In the case of nucleic acids, an HVR is where base pairs frequently change. This can be due to a change in the number of repeats (which is seen in eukaryotic nuclear DNA) or simply low selective pressure allowing a great number of substitutions and indels (as in the case of mitochondrial DNA D-loop and 16S rRNA). * In the case of antibodies, an HVR is where most of the differences among antibodies occur. This region is also called the complementarity-determining region. Because there already is a separate article for the antibody region, this article will focus on the nucleic acid case.

A hypervariable region (HVR) is a location within a sequence where polymorphisms frequently occur. It is used in two contexts: In the case of nucleic acids, an HVR is where base pairs frequently change. This can be due to a change in the number of repeats (which is seen in eukaryotic nuclear DNA) or simply low selective pressure allowing a great number of substitutions and indels (as in the case of mitochondrial DNA D-loop and 16S rRNA). In the case of antibodies, an HVR is where most of the differences among antibodies occur. This region is also called the complementarity-determining region. Because there already is a separate article for the antibody region, this article will focus on the nucleic acid case. ==Mitochondrial== There are two mitochondrial hypervariable regions used in human mitochondrial genealogical DNA testing. HVR1 is considered a "low resolution" region and HVR2 is considered a "high resolution" region. Getting HVR1 and HVR2 DNA tests can help determine one's haplogroup. In the revised Cambridge Reference Sequence of the human mitogenome, the most variable sites of HVR1 are numbered 16024-16383 (this subsequence is called HVR-I), and the most variable sites of HVR2 are numbered 57-372 (i.e., HVR-II) and 438-574 (i.e., HVR-III). In some bony fishes, for example certain Protacanthopterygii and Gadidae, the mitochondrial control region evolves remarkably slowly. Even functional mitochondrial genes accumulate mutations faster and more freely. It is not known whether such hypovariable control regions are more widespread. In the Ayu (Plecoglossus altivelis), an East Asian protacanthopterygian, control region mutation rate is not markedly lowered, but sequence differences between subspecies are far lower in the control region than elsewhere. This phenomenon completely defies explanation at present. ==See also== Cambridge Reference Sequence Genealogical DNA test Human mitochondrial DNA haplogroup mtDNA control region ==References== ==External links== DNA: Forensic and Legal Applications, Explanation of Hypervariable Regions

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