Mitochondrial DNA

Background

In addition to nuclear DNA, each cell contains mitochondrial DNA, suitably named for its location in the mitochondria. Mitochondrial DNA is used to create and store ATP, which is used to power the cell. It is theorized that mitochondria may have been bacteria adapted into the cell in a symbiotic relationship; the bacteria would receive nutrients from the cell in return for energy created from oxygen.

^ Mitochondria_______________________

Mitochondrial DNA is inherited only from the mother, because while the sperm and oocyte both contribute chromosomes, only the oocyte contributes cytoplasm and organelles. Mitochondria also have a high mutation rate- approximately 10 times as often as nuclear DNA. These two features make it possible to trace ancestry by comparing the mutations present in individuals to those of their mothers, grandmothers, great-grandmothers, etc., etc. Work in the 1980s by Alan Wilson and others at UC Berkeley created a family tree, hypothesizing that all humans alive today evolved from a single ancestor. This "mitochondrial Eve" probably existed in Africa about 200,000 years ago.

^ a family tree_________________________

Mitochondrial DNA is extremely valuable in science. Because it is more prolific than nuclear DNA, it can be used in cases where much time has passed and DNA has been severely degraded.

Procedure

Skin cells are obtained either by a saline mouthwash or root ends from scalp, eyebrow, or arm hairs. A region is amplified using PCR, which cycles the DNA through three stages: first, a 94°C incubation to denature the DNA, a 58°C incubation to bond the primers to their complementary sequences, and a 72°C incubation for DNA polymerase to create complementary strands. Because of the large quantity of mitochondrial DNA already present, it does not need to be cycled as long as nuclear DNA. Because of the similarity of mitochondrial DNA, the bands resulting from gel electrophoresis will appear to be the same. Samples may be submitted to the Sequencing Service  of the Dolan DNA Learning Center, which can generate sequences and post them on the internet.

Results

From our results, we saw that the band width and positions are nearly identical to the human eye. This is understandable, as all human beings on the planet today share 99.9% of their DNA. The similarity allows us to trace our evolution and understand how we compare to each other, as well as to other species.

The next step in this lab will be sending our samples in to be sequenced, so we can compare our DNA in greater detail.