What is Mitochondrial DNA?
Inherited From the Mother, mtDNA is Perfect for Cold Cases
DNA-based technologies have enormous forensic implications in the fight against crime. Mitochondrial DNA MtDNA is perfect for older, smaller or degraded samples.
Mitochondria are Structures Inside Cells
Mitochondria (singular: mitochondrion) are structures within cells that convert the energy from food into a form that cells can use. Each cell contains hundreds to thousands of mitochondria.
Mitochondrial DNA (mtDNA) is Useful for Identifying Victims of Mass Disasters
These energy producing mitochondria have their own DNA molecules that are used to create a DNA profile, which is called mitochondrial DNA or mtDNA. In humans, the mitochondrial DNA genome consists of about 16,000 DNA building blocks (base pairs), representing just a fraction of the total DNA in cells.
Because mitochondria are structurally strong and protect the DNA they contain, mitochondrial DNA is useful for identifying victims of mass disasters, like the Tsunami, where the nuclear DNA in the cells could have been degraded or damaged. It is also often used in Cold Cases.
Most cells in our bodies contain between 500 and 1000 copies of the mtDNA molecule, which makes it a lot easier to find and extract than nuclear DNA.
Nuclear DNA or nDNA
Usually, when we speak about DNA, we are talking about what is technically known as nuclear DNA or nDNA. It controls most aspects of our physical appearance and physical make-up. We know that every cell in our bodies contains two copies of it in the cell nucleus.
Mitochondrial DNA is Only Inherited from the Mother
What sets mtDNA apart is that, unlike nuclear DNA which is equally inherited from both father and mother, mtDNA is inherited only from the mother, because all our mitochondria are descended from those in our mother's egg cells.
This means that Mitochondrial DNA is passed from a mother to her children, which also makes it useful for tracing individuals’ maternal lineage. So, that while both sons and daughters inherit mtDNA from their mothers, only daughters can pass their mtDNA to their children.
Mitochondrial Eve - Out-of-Africa Theory
Imagine the mitochondrial DNA of all women living today, then that of all their mothers, and their mothers’ mothers. It is obvious that each set will be as small as or smaller than the previous set. Eventually the set will contain only the mitochondrial DNA of one woman - "Mitochondrial Eve".
The idea of a "Mitochondrial Eve" came from a 1987 paper by Rebecca Cann and coworkers supporting the Out-of-Africa theory that says that all modern humans descended from a common African ancestral population.
Cann's group reported that genetic diversity in mitochondrial genes of all living humans could be traced back to one woman who lived in Africa approximately 200,000 years ago.
nDNA versus mtDNA
Compared with Traditional nuclear nDNA analysis, Mitochondrial mtDNA offers three primary benefits to forensic scientists:
- Its structure and location in the cell make mtDNA more stable, enabling investigators to test older or degraded samples
- mtDNA is available in larger quantities per cell – smaller samples can be tested
- mtDNA can be extracted from samples in which nDNA cannot, especially hair shafts and bone fragments.
MtDNA – Maternal Lineage Test
mtDNA sequence analysis is a valuable tool for determining whether individuals are biologically related through their mothers’ side of the family. This is commonly referred to as a maternal lineage test. An mtDNA maternal lineage test works by comparing the mitochondrial DNA (mtDNA) sequences of two or more individuals.
People who are biologically related in this way will have similar mtDNA sequences, while individuals who are not will have dissimilar mtDNA sequences.
Mitochondrial DNA- mtDNA - Testing for Cold Cases
The rise of mtDNA testing in the field of forensics means that cases that were previously thought hopeless, may now be resolved. Mitochondrial DNA in human cells is often more robust and more plentiful than nuclear DNA. MtDNA typing can be performed on hair shafts, bone, and teeth. As a result, mtDNA testing has been widely utilized by investigators in "cold case" police units
Sources:
Mitochondrial DNA: Emerging Legal Issues – Edward K Cheng, Assistant Professor of Law, Brooklyn Law School.
Read the Very interesting story of the Mitochondrial Eve and Mitochondrial DNA in Fossil Hominids
Other Forensic Science Articles:
What is Low Copy Number (LCN) DNA?
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