The fiftieth anniversary of the discovery of DNA as the biological entity that holds the genetic information necessary to program a living cell was recently celebrated. Since then, microarray analysis has emerged as an important application of this fundamental knowledge, now making it possible to delineate the genetic expression of thousands of genes of one cell at one time.

Deoxyribonucleic acid, or DNA, is a long, double-helix molecule that contains all of the genetic information of a life form. This genetic information controls all of the life-sustaining functions inside each of an organism's cells by creating enzymes and proteins using another molecule called RNA. A gene is a segment of DNA that codes for a specific enzyme or protein, providing a blueprint for the synthesis of enzymes and other proteins and also specifies when these substances are to be made. Genes govern both the structure and metabolic functions of the cells and thus of the entire organism.

The complex interaction of genes with proteins has been the subject of various research endeavors. Because many diseases and disorders are caused by defective genes, understanding exactly how genes function can help treat many of these pathological conditions. Though most cells in our bodies contain the same genes, not all of the genes are used in each cell. Some genes can be turned on, or expressed, when they are needed, and turned off when they are not. Many genes are used to specify features unique to each type of cell. Liver cells, for example, express genes for enzymes that detoxify poisons, while pancreas cells express genes for making insulin [3]. To know how cells achieve such specialization, scientists need a way to identify which genes each type of cell expresses.

A way to examine the specialization in cells has recently been found with the help of biotechnology. Biotechnology is the use of microorganisms or biological substances to perform specific industrial or manufacturing processes such as production of certain drugs and synthetic hormones [1]. Molecular biologists started the process of biotechnology in the mid-1970s when they developed molecular cloning and DNA sequencing. A new technology now promises to advance biotechnology further. That technology is microarray analysis, sometimes known as biochip, DNA chip, DNA microarray, gene array, and DNA technology. Unlike the traditional methods in molecular biology that explore each gene separately, microarray analysis promises to monitor the whole genome on a single chip so that researchers can have a better picture of the interactions among thousands of genes simultaneously [3].

Microarray analysis uses DNA chips, which are glass surfaces that represent thousands of DNA fragments arrayed at discrete sites. Thousands of individual genes can be spotted on a single slide, forming a microarray. After spotting the individual genes on the surface, messenger RNA is labeled with a fluorescent dye and added to the DNA spots on the microarray. Due to a phenomenon called base-pairing, the RNA will stick to the gene on the DNA that created it, and therefore matches it. After washing away all of the RNA that did not attach to the DNA, the microarray is observed under a microscope [2]. Because the RNA only sticks to the DNA gene from which it originated, and because it is already known which gene each spot on the microarray represents, researchers can determine which genes are turned on in the cell. Using this technique, researchers can then test what genes are expressed and which ones are not in various diseased and healthy human tissues [3]. After comparing the results from these experiments, researchers then have the opportunity to determine what genes and proteins may be causing a particular disorder.

Currently, there are still a few problems with this new technique. One major problem stems, ironically, from its remarkable productivity. Scientists are having difficulty with managing the enormous volume of information produced by the microarrays. To reduce the data down to manageable amounts, biostatisticians must make basic assumptions about the behavior of genes. Another problem with microarray technology is that it requires specialized robotics and imaging equipment that generally are not commercially available as a complete system.

Nevertheless, the new advances in research using microarray technology show great promise in solving many current dilemmas in both medicine and molecular biology. Some of the varied applications of microarray technology are in the fields of gene discovery, disease diagnosis, pharmaceutical development, and toxicological research, or toxicogenomics [3]. The goal of toxicogenomics, for example, is to find correlations between toxic responses to toxicants and changes in the genetic profiles of the living things exposed to such toxicants, and microarray technology has the potential to do just that [3]. Microarray technology also has the capability to enable biotechnology and pharmaceutical companies to identify drug targets-the proteins with which drugs actually interact. Since it can also help identify individuals with similar biological patterns, microarray analysis can assist drug companies in choosing the most appropriate candidates for participating in clinical trials of new drugs. In the future, this emerging technology promises to help physicians decide which medications will be the most effective and will have the fewest side effects in individual patients. In other words, microarray technology has a tremendous potential to significantly improve many aspects of medicine, research and perhaps even our everyday lives.

Nadia is a first-year student with plans to major in Bioengineering. She aspires to enter the field of medicine.