Mitochondrial DNA (mtDNA) is a continuous circle of 16569 genetic bases, each appearing at a distinct marker location. Locations are designated by number from 00001 to 16569.

Locations on the mtDNA circle from 16001 to 00579 are most useful for recent genealogy research. This range of locations is called the "D-loop" or the "control region". The D-loop can be divided into three regions called HVR1 (16024 to 16365), HVR2 (00073 to 00340), and HVR3 (00438 to 00574).

The table below displays the range of locations reported by various companies for each HV region. Please note that these ranges don't always correspond to the technical HV Region definitions.