Scientists have long imagined being able to make specific changes
to the genetic code of a cell or organism.
A revolutionary, genome-editing technology makes this possible,
using an RNA guided protein called Cas9.
Cas9 searches through the cell's vast genetic material
until it finds a sequence of DNA that 
matches the sequence of its programmable guide RNA.
The guide RNA enables Cas9 to open the DNA helix,
then to position two molecular blades to cut each strand of the DNA double helix.
Repair enzymes seal the gap in the broken DNA,
sometimes by inserting new genetic information,
supplied by the cell or the experimenter.
In this way, disease-causing mutations
can be corrected
by changing the underlying genetic code.
Scientists are now using this Cas9 technology
for research applications in human health,
agriculture, and bioenergy.
