Every human cell has a "second" genome, found in the cell's energy-generating organelle, the mitochondrion. In fact, each mitochondrion has several copies of its own genome, and there are several hundred to several thousand mitochondria per cell. This means that the mitochondrial (mt) genome is highly amplified. While each cell contains only two copies of a given nuclear gene (one on each of the paired chromosomes), there are thousands of copies of a given mt gene per cell. Because of this high copy number, it is possible to obtain a mt DNA type from the equivalent of a single cell's worth of mt DNA. Thus, mt DNA is the genetic system of choice in cases where tissue samples are very old, very small, or badly degraded by heat and humidity.

Under good circumstances - working from fresh cell samples - mt DNA is the easiest human DNA to amplify by PCR. This experiment examines a 440-nucleotide sequence from the noncoding region of mt genome. Hand cycling is a realistic alternative to automated thermal cyclers, and the high yield of amplified product can be visualized in an agarose gel with a variety of stains.

Because each student is amplifying the same region, the gel electrophoresis results will also be the same for each. However, amplified student samples may be submitted to our Sequencing Service, which will generate student mt DNA sequences and post the results on our Sequence Server. Comparison of control region sequences reveals that most people have a unique pattern of single nucleotide polymorphisms (SNPs). These sequence differences, in turn, are the basis for far-ranging investigations on human DNA diversity and the evolution of hominids.

M I T O C H O N D R I A L  C O N T R O L  R E G I O N

DNA Learning Center, Cold Spring Harbor Laboratory
Noncommercial, educational use only.