Mitochondrial Madness

By Alaina Grantham
Rotunda ReporterLast summer my mom, sister and I miraculously had the same day off work and in traditional home-school fashion, decided to go to a museum. After a brief debate settled by rock paper scissors, we decided to go to the National Museum of Health and Medicine at the Walter Reed Military Base in Bethesda, Md.

As a biologist, I had wanted to go to this museum for years, ever since I had learned about the five-pound hairball on display standing as a constant reminder to all little girls who would chew their hair. In spite of my excitement, my mother , the history major; and my sister, the business major ,were not as excited for a day filled with science as I was, but we were still happy to be going on a museum adventure together.

Once we arrived at the museum, we followed the crowd past displays on medical history, plastic surgery and heart disease. Eventually, we ended up in front of the exhibit that explained identification of remains: specifically, the remains of fallen soldiers.

The exhibit outlined the history of identification and showed its application during wars the United States had participated in. It started with visual identification, continued with dental records and finally ended with DNA identification, which in the absence of a comparative DNA samples uses mitochondrial DNA.

Because this is all the display said on the subject of mitochondrial DNA, I, being the somewhat nerdy science geek I am, started to explain to my family how it could be used in the identification of unknown persons.

Mitochondrial DNA is different from nuclear DNA, so different that scientists suggest that the primitive mitochondria invaded early cells and brought its own DNA with it. This theory, supported by physical characteristics of the mitochondrial DNA, suggests that after the initial invasion both the cell and the mitochondria developed a symbiotic relationship over the millennia until they work so seamlessly together that they are considered one entity. Where the nuclear DNA provides the bulk of genetic material, the mitochondria provide the energy for the cell to survive.

The reason why mitochondrial DNA is useful in identifying an unknown body stems from the way the DNA is inherited, which is different from nuclear DNA. Nuclear DNA is what is typically thought of when DNA is mentioned, a combination of the mother and father's DNA. The mother's contribution comes from the egg, and he father's comes from the sperm.

Because the sperm is designed for travel it "packs light" and is essentially nothing more than a nucleus modified for movement, leaving no room for the mitochondria to be carried over from the father. This means every mitochondrion originated from the mother, and as such carries nearly the exact mitochondrial DNA that she had.

With such close similarities, we can compare the mitochondrial DNA of an unknown soldier to a database of mitochondrial DNA from mothers and establish relationships without having an original sample on file from the soldier.

It was then that I turned to my mom and sister; my mom shook her head twice to sort through all the biology I had thrown at her.

"Why can't the father's mito-things be used?" My mom asked. I started to explain again the space issues connected with sperm, but before I could finish she interrupted me and said, "That's sexist," and walked away, having reached her monthly allotment of science.