DNA chip, also called a DNA microarray or biochip, is a technology developed in the late 1990’s that enables scientists to study hundreds or thousands of genes at once. Genes carry the chemical instructions that determine an organism’s traits. These instructions are stored in DNA (deoxyribonucleic acid), the chief substance of chromosomes. Even the simplest multicellular organisms have thousands of genes. In the past, scientific studies of genes have focused on identifying individual genes and the products, such as proteins, that they produce. However, biologists know that the thousands of genes that make up the genome (entire set of genes) of an organism interact in complex ways. DNA chips allow biologists to study and monitor the action of many genes under different conditions and observe how genes work together in living organisms.
DNA chips are often similar in appearance to microscope slides and are typically made of glass, silicon, nylon, or plastic. Using automated machinery, scientists spot (place) single-stranded segments of DNA, called probes, representing individual genes onto the surface of the DNA chip. Synthetic, single-stranded sequences of DNA called oligonucleotides, which may or may not contain genes, can also serve as probes. A single chip may contain tens of thousands of individual DNA spots per square centimeter (0.16 per square inch), arranged in an ordered array (grid pattern). Computers track the gene or DNA sequence represented by each spot.
DNA chips allow scientists to identify unknown genes or determine the activity of genes from a sample of DNA. The samples, called targets, can be obtained from the cells or tissues of any organism. Single-stranded target DNA sequences are first labeled with tags or reporter molecules, such as fluorescent dyes that glow green or red when exposed to ultraviolet (UV) light. The sample DNA strands are then applied to the array of spots on the DNA chip. The DNA sequences from the sample bind to their complementary single-strands on the chip. Sequences that do not have any complementary strands on the chip remain unattached and can be washed away. After the DNA sequences from the sample have had time to bind, a scanner is used to read the chip. The type of scanner used depends on the specific tags used on the samples. For example, when fluorescent dye is used as a tag, the scanner may use UV light to read the chip. A color print-out of the surface of the chip can then be made. The pattern of colors on the chip can be used to determine the specific genetic activity in the DNA sequences from the sample.
The development of DNA chips has revolutionized many areas of research in biology and medicine. New and faster methods for diagnosing disease, detecting toxic (poisonous) substances, developing new drugs, and exploring the genetic relationships of living organisms are possible with this technology. DNA chips are also important in genomics, the study of genes as they exist in living things.
See also DNA ; Gene mapping ; Genomics .
