T H E O R Y
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.
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.