Mitochondrial DNA test

From ISOGG Wiki

Map of human migration out of Africa, according to mitochondrial DNA. The numbers represent thousands of years before present time. The blue line represents the area covered in ice or tundra during the last great ice age. The North Pole is at the centre. Africa, the centre of the start of the migration, is at the top left and South America is at the far right.

A mitochondrial DNA test (mtDNA test) traces a person's matrilineal or mother-line ancestry using the DNA in his or her mitochondria. mtDNA is passed down by the mother unchanged, to all children. If a perfect match is found to another person's mtDNA test results, one may find a common ancestor in the other relative's (matrilineal) "information table". However, because mtDNA mutations are very rare, the match will not necessarily be within a genealogical time frame.

Note that in cultures lacking matrilineal surnames to pass down, neither relative above is likely to have as many generations of ancestors in their matrilineal information table as in the above patrilineal or Y-DNA case.

What gets tested

mtDNA by current conventions is divided into three regions. They are the coding region (00577-16023) and two Hyper-Variable Regions (HVR1 [16024-16569], and HVR2 [00001-00576]). All test results are compared to the mtDNA of a European in haplogroup H2a2a. This early sample is known as the Cambridge Reference Sequence (CRS). A list of single-nucleotide polymorphisms (SNPs) is returned. The relatively few "mutations" or "transitions" that are found are then reported simply as differences from the CRS, such as in the examples just below.

The two most common mtDNA tests are a sequence of HVR1 and a sequence of both HVR1 and HVR2. Some mtDNA tests may only analyze a partial range in these regions. Some people are now choosing to have a full sequence performed, to maximize their genealogical help.

Understanding test results

The most basic of mtDNA tests will sequence hyper-variable Region 1 (HVR1). HVR1 nucleotides are numbered 16024-16569. Some test reports might omit the 16 prefix from HVR1 results, i.e. 519C and not 16519C.

More extensive tests will also sequence Hyper Variable Region 2 (HVR2). HVR2 nucleotides are numbered 00001-00576.

See also

• mtDNA testing comparison chart

External links

• ISOGG chart showing path of mtDNA transmission

Licence

This article is licensed under the GNU Free Documentation Licence. It incorporates material from the Wikipedia article "Genealogical DNA test".