Extraction, Amplification and Electrophoresis of Human Mitochondrial DNA

   Imagine that we could trace our family tree back to the first human ever to set foot on earth. Well actually, it doesn't take much of an imagination, as the study of mitochondrial DNA may offer us just that possibility. From an early age, everyone learns what DNA is. Mom and dad pass some stuff to their children that makes them look and act alike. But a lesser known fact is that there is a different type of DNA that we obtain solely from our mothers.
   In all eukaryotic organisms are organelles called mitochondria. It is theorized that mitochondria were once their own organism but were engulfed by a more sophisticated eukaryotic cell. Mitochondria utilize oxygen from the atmosphere to create energy that fuels the functioning of the cells, making it one of the most vital organelles in our bodies.
   Mitochondria actually carries its own set of DNA that codes for the machinery that allows it to synthesize energy (ATP). This DNA comes directly from our mothers, creating a lineage based on nearly-identical mitochondrial DNA, differing only due to mutation. But why do we procure this DNA just from our mothers? Sperm, hosting the male genome, must be small and elusive to make its way to the female egg, so it carries little more than the necessary DNA, with just enough mitochondria to power its journey. The egg, on the other hand, contains all the typical organelles. Therefore, the mother is the one to contribute its cytoplasm and organelles, including the mitochondria, to the zygote.

   The mitochondrial (mt) genome was sequenced far before the human genome because it only contains 16,569 nucleotides and 37 genes. The mt genome has few introns, but it does have one long non-coding stretch that is highly mutative. The region's supervariable quality creates SNPs that help establish familial relationships. Based on rates of mutation, scientists determined that the "mitochodrial Eve" first appeared 200,000 years ago in Africa- the origin of modern humans. The non-coding control region is especially useful because each cell contains hundreds of thousands of copies of each mt gene.
   For our experiment, we will use a template DNA instead of our own. First, we will add Chelex beads to the sample to break open the membrane and destroy ions that block PCR, and then we will separate the cells by vortexing. Next, we will amplify the extracted DNA through the process of PCR that I have described thousands of times. As a refresher, PCR requires DNA polymerase, primers, DNA nucleotides, and DNA ligase. It is essentially the rapid, controlled process of DNA replication. We will use specific primers that will target a segment of the non-coding region of mt DNA.
   Finally, we will run our mt DNA samples through gel electrophoresis, in which the DNA molecules will travel a certain distance, depending on their length (number of nucleotides).

MOMS

           GGel Electrophoresis

Our lab was a success, with everyone's mitochondrial DNA showing up on the gel. All our mt DNA strands were the same size, so they traveled the same distance on the gel. Because of this, we cannot make any differentiations between our mt DNA. For a small fee, however, we could send it off to be sequenced by a lab. We just might do that...