All at once
Using a small DNA chip, researchers have determined the activity of all genes in an organism simultaneously in a single experiment. After completion of the Human Genome Project, immediate examinations of the human genome would also be possible. A living being's genome is often referred to as a blueprint, but it's actually more like a city's phone book: it contains the names and addresses of thousands of individuals, but reveals nothing about how they spend their time. In the case of the genome, these "individuals" are the genes, most of which are active only intermittently. Until now, it has not been possible to find out which genes in a living being are switched on and which are switched off at a certain moment. For this task, David Lockhart and his research group at Affymetrix developed a "DNA chip" with which they could check the activity of all 6200 genes in baker's yeast at the same time.
The chip consists of a grid of short pieces of DNA, each of which represents a specific gene on the yeast chromosome. When genes are active, an associated messenger RNA (mRNA) is made. This mRNA binds to the corresponding pieces of DNA on the chip, which can be quantitatively detected with fluorescent dyes.
Lockhart studied yeast grown under two distinctly different conditions: in a minimal medium, containing only the most necessary substances, and in an environment rich in nutrients and energy sources. They put mRNA from both samples on the chip and determined the resulting fluorescence. By concentrating around 260,000 DNA sequences on an area of around 2 square centimetres, the activities of all genes could be measured simultaneously.
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