How Do Arrays Work?
DNA arrays come in many varieties. Whether they are created by scientists or produced commercially by one of several companies, arrays depend on the same basic principle: Complementary sequences of nucleotides stick to, or hybridize to, one another. For example, a DNA molecule with the sequence -A-T-T-G-C- will hybridize to another with the sequence -T-A-A-C-G- to form double-stranded DNA. For the past 25 years, scientists have been using hybridization as a standard technique to detect specific DNA or RNA sequences. A single-stranded DNA molecule with a known sequence is labeled with a radioactive isotope or fluorescent dye and then used as a probe to detect a fragment of DNA or messenger RNA (mRNA, the molecule that is produced when a gene is turned on or expressed ) with the complementary sequence. For example, if a researcher wants to know whether gene A is expressed in a particular tissue, the researcher would make a radio-labeled DNA probe by using a small piece of gene A, isolate
