Why you need to know about DNA Chips

• They are astonishingly powerful. They allow scientists to quickly and inexpensively do experiments they could only dream about just a few years ago--like tracking how the expression of every single gene in the human genome changes in response to an experimental variable. Not only that.....
• They are cheap and fast. Chips will make it possible to find out not just the average human genetic sequence, but about your personal genetic sequence. Therefore....
• They have consumer applications. Sometime in the coming decade, you will likely see these devices popping up in your doctor's office (to choose treatments based on individual genotype), or at your local police station for use in criminal investigations. That means....
• They are becoming big business. Analysts estimate that the annual sales of DNA chips will exceed 1 billion dollars within just a few years.

What you need to know about DNA Chips
Here are some basic facts about DNA chips. Don't memorize this list, but read through it. After reading this issue of Snapshots, you should be able to say, "OK, I knew that," about each point.

• “DNA chip” is slang for DNA microarray.
• DNA chips are a revolutionary technology. They speed up research, helping scientists understand the primary sequence of the human genome, now almost complete. They will also allow doctors to get important genetic information from individual patients and thus choose the best treatments.
• Each of the strands in a bit of double-stranded DNA is complementary to the other. Adenine (A) is opposite thymine (T), cytosine (C) is opposite guanine (G). So, the sequence CCATGA would be complementary to GGTACT. Complementary DNA strands separate on gentle heating. They bind again when cooled.
• A DNA chip is made of many different DNA sequences stuck to a flat surface. Each spot on the surface contains a different sequence.
• You can use a single strand of DNA to "probe" a solution for that strand's complement: Put in the probe, slosh it around, pull it out. If the complement is in there, it will bind onto the probe.
• A DNA microarray allows you to probe a solution for thousands of different sequences all at once. Stick each different probe at a specific spot on a flat surface. Slosh a solution containing the unknown single-stranded sequence over it. Rinse. Look for the spots where the probes found their complements.
• Microarrays can have tens of thousands of spots. This means they can look for tens of thousands of DNA sequences all at once.
• A sequencing array is made of many different short DNA sequences. Researchers use these to find the sequence of an unknown bit of DNA. A researcher chops the unknown sequence into short bits, sees where the bits bind on the array, deduces the sequences of all the short unknown bits, then reassembles the overlapping sequences into one long sequence.
• An expression array is made up of many different long DNA sequences, each complementary to every mRNA sequence that a certain cell can make. Researchers use these to study moment-to-moment changes in which genes are turned on or off. A researcher breaks a cell preparation open, extracts all the mRNA sequences it contains at that moment, and puts those on the expression array to see which ones are there. This tells the researcher which genes in the cell were turned on-being expressed, making mRNA-at the moment the cell broke open.
• Researchers love DNA chips because they give a huge amount of information, fast, at low cost.
• Doctors will soon learn to love them because there are many times when a doctor would like to know something about a patient's genes (such as whether the patient is likely to respond well to a certain drug). When the price comes down enough, microarrays will likely become routine tools in the doctor's office.