What is Mitochondrial DNA (mtDNA)?
Our body is made up of cells.
All cells comprise smaller components called cell organelles, each with a specific function that it performs within the cell.
One such organelle is the mitochondria, responsible for converting energy from food into a form the cell can use.
Since the mitochondria produce energy, it is also called the powerhouse of the cell.
Each cell contains hundreds of mitochondria floating in a fluid in the cell called the cytoplasm.
While most of the DNA in a cell is packed into a structure called the nucleus, a small amount of DNA is also found to occur in the mitochondria.
This genetic material is called mitochondrial DNA or mtDNA.
Almost all the cells in our body contain hundreds of copies of mitochondrial DNA, unlike 23 pairs of chromosomes in autosomal, Y- and X-DNA (the DNA you receive from your parents).
The mitochondrial DNA contains 37 genes, all of which are required for normal mitochondrial function.
13 of these genes give instructions for making enzymes involved in oxidative phosphorylation.
Oxidative phosphorylation is a process that uses oxygen and simple sugars to create ATP (the main source of energy for the cell).
The remaining genes in the mitochondrial DNA provide instructions for producing molecules responsible for protein synthesis and other functions.
Mitochondrial DNA Inheritance
We inherit our mitochondrial DNA from our mother. For this reason, we share our mtDNA with our mothers, sisters, brothers, maternal grandmothers, aunts, uncles, and other maternal relatives.
Since mitochondrial DNA undergoes a high frequency of abnormal changes (called mutations), the mtDNA sequences between closely related maternal relatives may differ.
Mitochondrial DNA is complex; therefore, it may be difficult to predict how mtDNA mutations pass from the mother to her child.
Mitochondrial DNA Disorders
These are chronic (long-term) genetic disorders that occur when the mitochondria cannot produce enough energy for the cell to function.
These disorders are usually inherited from the mother.
Mitochondrial disorders can affect any part of the body. A few common mitochondrial disorders are:
- Alzheimer’s disease
- Muscular dystrophy
- Diabetes
- Cancer
- Lou Gehrig’s disease
Mitochondrial disorders are fairly common; around one in 5,000 people are diagnosed with a condition yearly.
Mitochondrial inheritance
Mutations in the mtDNA that cause mitochondrial disease are inherited exclusively from the mothers, and there is a 100% chance that every child in the family will inherit the condition.
Mitochondrial DNA Testing
This test helps people trace their matrilineal or mother’s line of ancestry through their mitochondria.
Since everyone has mitochondria and each individual inherits them from their mother, people of all genders can take an mtDNA Test.
Mitochondrial DNA testing uncovers an individual’s mtDNA haplogroup (the ancient group of people from whom their matrilineage descends. Apart from this, mtDNA testing also helps determine a common maternal ancestor or look for diseases inherited from this line.
How’s It Done?
Once a blood sample is collected for the mtDNA testing, it is transported safely and securely to the laboratory.
In many cases, the sample collection may happen in the lab.
Once the sample has been prepared and the circular mtDNA isolated, it is divided into three sections:
- Hypervariable control region 1 (HVR1)
- Hypervariable control region 2 (HVR2)
- Coding region (CR)
Who Does The Test?
Several genetic laboratories and companies perform mtDNA testing.
You can look for the one closest to you.
Always check for the necessary accreditations and certifications of the laboratory before going through with the test.
Who Should Take The Test?
Anyone can take an mtDNA test for the following reasons:
- To know more about their maternal ancestors
- To establish maternity
- To determine diseases or disorders that are running in the maternal family
- To look for missing maternal relatives
How Much Does Mitochondrial DNA Testing Cost?
The cost for mitochondrial DNA testing varies at different laboratories based on their machines, technology, and experience.
The cost of the test can also vary depending upon whether you choose to use a self-test kit or a laboratory-based one.
Mitochondrial DNA Testing: Benefits and Challenges
While regular DNA gives plenty of information about our ancestry and lineage and helps establish paternity, mitochondrial DNA offers several benefits as well:
- It has the intrinsic ability to resist degradation and remains viable longer than nuclear DNA.
- It has a higher copy number inside the cell compared to nuclear DNA.
- It is a powerful investigating tool that has been used to solve several challenging murder cases in the past.
- It gives us a deeper insight into the ancient human diet.
- It has helped Egyptologists and other researchers study mummies better.
The primary challenge in mtDNA analysis is that mtDNA shows heteroplasmy or the possibility of mutations.
This gives rise to two different mtDNA sequences.
So, at the time of analysis, there should be at least two differences between the sample and reference material.
Summary: Mitochondrial DNA Testing
- Mitochondrial DNA or mtDNA is found in the mitochondria of each cell and is inherited by an individual from their mother.
- Mitochondrial disorders caused by mtDNA show 100% inheritance exclusively from the biological mother.
- Mitochondrial DNA testing helps people trace their mother’s line of ancestry.
- People of all genders can take an mtDNA analysis test if they want to learn more about their maternal ancestors or determine disorders in the family.
- The main challenge in mtDNA analysis is heteroplasmy.
References
- https://www.genome.gov/genetics-glossary/Mitochondrial-DNA/
- https://medlineplus.gov/genetics/chromosome/mitochondrial-dna/
- https://en.wikipedia.org/wiki/Mitochondrial_DNA
- https://support.ancestry.com/s/article/Y-DNA-mtDNA-and-Autosomal-DNA-Tests?language=en_US
- https://www.genealogyexplained.com/dna-testing/mitochondrial-dna-testing/
- https://dps.mn.gov/divisions/bca/bca-divisions/forensic-science/Pages/dna-mitochondrial.aspx
- https://www.baylorgenetics.com/mitochondrial/
- https://www.nature.com/scitable/topicpage/mtdna-and-mitochondrial-diseases-903/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6562384/
