Scientists can put not just a hundred but hundreds of thousands of distinct DNA sequences on a microscopic grid a few centimeters across. DNA chips can gather an incredible variety of data very quickly. And because chips can be mass-produced, they will likely be very inexpensive in the near future. That will allow easy collection of genetic information from many, many individuals, opening up all kinds of opportunities to help doctors diagnose and treat their patients. Then a ribosome translates the mRNA sequence into the string of amino acids that makes up the protein.
Cells constantly switch genes on or off as conditions change.
For example, Patrick Brown and his colleagues at Stanford University wanted to find out the details of how yeast cells make spores. Then, they ground up a bunch of resting yeast cells, which of course contained an mRNA corresponding to each gene that was active at the moment the cells hit the blender. Next, the researchers spread this mixture over the surface of the chip. Only the spots corresponding to genes that were actively churning out their mRNA lit up, because these were the only spots on the chip that had found their complementary sequence. This first experiment gave Brown and his colleagues a baseline.