Mitochondrial DNA: Connecting Generations

The need to put ourselves into a historical family context and discover our ancestry seems to be a quasi-innate need in each of us. Centuries-old family trees, ancestral worship in various cultures, theological debates on the afterlife, and even Darwin’s theory of evolution all point to a very basic human need: to know where we came from.  This article discusses advancements in maternal lineage testing that allows us to evaluate mitochondrial DNA to assist us in this quest.

Your Ancient Ancestral Lines

An ancestry DNA test can be used to help you discover your ethnic and ancestral blend by testing the indelible marks your ancestors left on your own genetic makeup. By comparing your DNA to the hundreds of records of studied anthropological groups and tribes in genetic databases, an ancestry test can reveal which ancestral group your genetic blueprint most closely matches. Furthermore, since each studied anthropological group originated in a known geographic region, your DNA can be linked to the place your ancestors came from. It is important to keep in mind, however, that because ancestry testing detects your ancient origins and will take you back thousands of years, a DNA test likely will not link you to specific countries because your ancestral roots are far older, predating the political world map we have today.

Honing In: Your Maternal Roots

Certain tests can specifically focus on the aspect of your ancestry you are most eager to discover. You might want to exclusively trace your ancient maternal ancestry with a maternal lineage ancestry test. This test will locate your maternal origins through the analysis of your mitochondrial DNA, a special type of DNA which is found inside one of the components within the mammalian cell, known as mitochondria.

What Are Mitochondria?

Mitochondria are capsule-shaped cell organelles which can be thought of much like batteries – they are responsible for generating the energy the cell needs to function. Mitochondria are often referred to as “the powerhouse of the cell” and float freely within the cell. Energy is generated in the form of a molecule known as Adenosine Triphosphate (ATP), which is mainly created inside the mitochondria. Cells that require more energy, such as those making up muscle tissue, have a higher number of cell mitochondria inside them. A secondary function of mitochondria is to synthesize proteins which the organelles require for their own use.

MtDNA vs. Nuclear DNA: What Are the Differences?

The mammalian cell contains two types of DNA: mitochondrial DNA (mtDNA) and nuclear DNA. Nuclear DNA and mtDNA are found in entirely different parts of the cell: mtDNA is found in the cell mitochondria with many copies found in each cell, while nuclear DNA is found in the cell nucleus with just one copy per cell. The two types of DNA differ mainly in structure as well as in the number of genes carried in each. Nuclear DNA contains about 20,000 encoding genes while mtDNA carries just 37 genes. Mitochondrial DNA carries characteristics inherited from a mother in both male and female offspring. Thus, siblings from the same mother have the same mitochondrial DNA. In fact, any two people will have an identical mitochondrial DNA sequence if they are related by an unbroken maternal lineage. An mtDNA test cannot distinguish the type of relationship between people tested because all individuals from the same maternal line will share the exact same mitochondrial DNA profile, making it impossible to know if individuals are grandmother and grandchild, mother and child, maternal aunt and nephew, etc. Given the inheritance pattern of mitochondrial DNA, diseases associated with the mitochondria, such as Leigh syndrome and Leber's hereditary optic neuropathy (LHON), are solely maternally inherited.

Maternal Haplogroups

We have already mentioned that mitochondrial DNA is a special type of DNA that you inherited from your mother, which your mother, in turn, inherited from her mother, and so on. Discovering the maternal side of your lineage is possible thanks to mtDNA and this test can be carried out by both males and females to help locate one’s maternal origins and indicate where their ancestral mothers came from.

A great advantage of mitochondrial DNA analysis is the fact that it is relatively stable. It is also retained in bodies for several years after death. In fact, it has been possible to analyze fossil caveman DNA with the help of mtDNA analysis.

When a maternal lineage test is carried out, scientists look at specific mutations or polymorphisms. These mutations or polymorphisms are changes in the sequences of an individual’s genetic code and would have been inherited from ancestors and passed down from generation to generation. Due to the specificity of these genetic changes they become accurate lineage markers which can be linked to specific mitochondrial haplogroups (think of a haplogroup as your genetic family clan – all individuals who share the same haplogroup also share the same set of DNA markers). These haplogroups are also associated with the earliest human migrations and can be linked to specific geographic locations. There are 25 known mtDNA haplogroups.

The Regions Tested

There are three regions on your mitochondrial DNA which can be analyzed to reveal information about your maternal ancestry and confirm your haplogroup affiliation. These regions, readily identified in evolutionary studies, are called hypervariable regions and are abbreviated as HVR (the term “hypervariable” refers to the variable number of repeated sequences on the genome). In most cases analysis of Hypervariable region 1 (HVR) will be enough to discover a person’s haplogroup affiliation. In some cases, however, further testing of different regions, namely HVRII and HVRIII, will be required.

Discovering one’s maternal roots through DNA testing is a great way of discovering ancient ancestral origins – but it is just one tool of many. For a comprehensive approach, combine DNA analysis with the services of expert genealogists who can not only help you with the interpretation of your DNA test results, but also help you trace a family tree and find out more about your specific ancestors. To learn more about hiring Legacy Tree Genealogists for help, visit http://www.legacytree.com/services.

References:

“Maternal Lineage Test,” EasyDNA, https://www.easy-dna.com/maternal-lineage-test/, accessed 14 December 2016.

Valerio Carelli, “Keeping in Shape the Dogma of Mitochondrial DNA Maternal Inheritance,” PLOS Genetics, 11.5 (May 2015), e-journal, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4431736/, accessed 14 December 2016.

“Mitochondria,” Molecular Expressions: Cell Biology and Microscopy Structure and Function of Cells and Viruses, https://micro.magnet.fsu.edu/cells/mitochondria/mitochondria.html, accessed 14 December 2016.

2016. Deena T. Kochunni, “Difference Between Mitochondrial DNA and Nuclear DNA,” Major Differences, http://www.majordifferences.com/2015/05/difference-between-mitochondrial-dna.html#.WDW2JvnyvIU, accessed 14 December 2016.

“Mitochondrial DNA,” Wikipedia, https://en.wikipedia.org/wiki/Mitochondrial_DNA#Mitochondrial_inheritance, accessed 14 December 2016.