This tutorial is Part 5 of a 10 part series.
Part 1, What is mtDNA?
Part 2, Facts about mtDNA
Part 3, Structure of mtDNA
Part 4, Ancestral Markers in mtDNA
Part 5, Detecting Markers in mtDNA <<== You are here
Part 6, Tracing Ancestry with mtDNA
Part 7, The Cambridge Reference Sequence
Part 8, mtDNA Test Types
Part 9, mtDNA Haplogroup Determination
Part 10, mtDNA Subclades
A basic understanding of DNA testing techniques will help you to understand the science behind DNA ancestry testing.
DNA Testing 101
The entire genetic sequence of the mtDNA region tested is uncovered using a sequencing method called "Sanger Squencing". DNA sequencing is a special process which is used to read the chain of nucleotides in a specific segment of your DNA, much like reading a book.
This technology allows the lab read the entire genetic code of a whole section of your mtDNA. The following report is an example of the results of a sequencing test in the HVR1 region of an individual’s mtDNA.
As you can see, all of the nucleotides in HVR1 region (locations 16001 to 16520) have been decoded. All mutations detected in the sequence are indicated in pink.
The benefit of DNA Sequencing technology is that it can accurately read entire lengths of your DNA and represents the most comprehesive way to test mtDNA. The drawback of DNA Sequencing technology is that only approximately 400 to 500 nucleotides can be read at a time (in one run) so it is very expensive to perform.
Sequencing technology can be used to sequence the entire HVR1, HVR2 and Coding regions of your mtDNA. The HVR1 region is approximately 500 nucleotides in length (spans location 16,000 to 16,569). The HVR2 region is approximately 400 nucleotides in length (spans locations 1 to 400). The Coding region is approximately 15,500 nucleotides in length (spans location 400 to 16,000).
DNA Sequencing technology is the most comprehenstive way to detect mutations in the mtDNA. The HVR1 and HVR2 reigons are the most widely studied region of the mtDNA for ancestral studies and a great starting point for beginner genetic genealogists.
The Coding Region of the mtDNA is extremely large and very expensive to sequence due to its large size. While the Coding Region does not have a high concentration of mutations, the mutations that it does carry are highly informative. Testing the mutations in the Coding Region is necessary in order to confirm an individual's haplogroup and subclade. Once the HVR1, HVR2, and Coding regions are fully sequenced, the entire mtDNA will be uncovered an no further mtDNA testing will ever be required. Sequencing all three regions will allow the laboratory conclusively confirm your mtDNA Haplogroup and mtDNA Subclade. Furthermore, as more mtDNA data becomes availabe and the mtDNA tree continues to grow, you will continue to receive the latest classifications and updated results if all three regions of your mtDNA have been sequenced.