Mitochondrial DNA Explained

Mitochondrial DNA is a very useful tool in forensic science. It has been used to identify human remains and perpetrators of a crime. It has also been used to determine ancestry.


In traditional DNA testing, nuclear DNA is used. Nuclear DNA (nDNA) can be removed from any nucleated cell. However, there are cells that do NOT contain nuclear DNA. These cells are called non-nuclear DNA cells. Where else is DNA found? Mitochondria contain DNA. Mitochondria are tiny organelles that live within the cytoplasm of a cell. Their role in a cell is to produce energy used for the cell's metabolic processes.

A minute amount of DNA is found within the mitochondria. Each cell contains many tiny mitochondria organelles. Mitochondrial DNA (mtDNA) is important for several reasons:

mtDNA

• passes from parent to offspring via the maternal lineage

• is found in places where nDNA can not be found

• rarely mutates

• is highly stable

Your mitochondrial DNA comes unchanged from only your mother. She receives hers from her mom, and her mom from her mom, and so on and so forth.

Upon fertilization, the mother contributes to the zygote her egg AND half of her DNA. The father, on the other hand, only contributes half of his DNA via the sperm. The sperm then degenerates after passing its genetic material into the nucleus of the egg cell. Therefore, all the cellular parts of the developing zygote are contributed from the mom, including the mitochondria. As the zygote divides and multiplies, these mitochondria are duplicated and passed on, parent organelle to offspring organelle, parent organelle to offspring organelle. This means that all the cells of a body have mtDNA that are consistent with that of the mom.

Genetic mutation of mtDNA is thought to happen about once every 6,000 years. This means that mtDNA is highly stable unlike nDNA. This also means that you essentially have the same mtDNA as your mom, your maternal grandmother, and all your maternal ancestors from hundreds or even thousands of years ago. For this reason, you can accurately trace back your maternal heritage through several generations.

Because of mtDNA's high stability, forensic scientists can many times remove it from the bones and teeth of very old skeletons and thus utilize it to determine the maternal lineage of skeletal remains. Mitochondrial DNA can also be found in some tissues where nuclear DNA normally does not exist. For instance, dead cellular debris can be found in human hair. However, the only thing that is living in human hair the follicle, where it is rich in nDNA. Nuclear DNA can be extracted from here and used for DNA profiling and matching. Simply put, hair that has been pulled out during a struggle or shed with its follicular bulb attached can be a rich source of nDNA.

Consider what happens if CSI's find human hair that has been cut and there is no follicular bulb attached? This hair can still provide clues.

As hair grows, the cells of the follicular bulb multiply, undergo transformation, and become an integral part of the growing hair. Part of this change includes the loss of the nucleus from each cell. Therefore, this hair is absent of nDNA, and the dead cells that are an integral part of the growing hair may contain mtDNA. If this is the case, mtDNA can be isolated and used for identifying the person to whom the hair belongs.

The next time you watch your favorite CSI program and see what they do with trace evidence such as human hair, you will know why they focus on the hair follicle for nuclear DNA and the hair for mtDNA.


Referance: http://ezinearticles.com/?Forensic-DNA-Analysis----What-is-Mitochondrial-DNA?&id=909578