DNA Arrays for Genetic Analyses and Medical Diagnosis

During the past decade we have witnessed remarkable advances in molecular biology, the scientific discipline that studies the molecular basis of heredity, genetic variations, and the expression patterns of genes. While genetic engineering may appear to be a new science, the techniques that are in use today are the result of a series of discoveries made over a period spanning more than 125 years. In the “Genome Era” we are able to sequence whole genomes effectively and relatively quickly. Magazines and television routinely report advances in “gene therapy” and transgenics procedures, which would have been unimaginable even a few years ago. In 2001, Human Genome Project leaders announced the completion of a “working draft” DNA sequence of the entire human genome: the postgenomic era begins. The availability of DNA sequences from genomes of the several organisms, and in particular from the human genome, has prompted the development of new techniques for tracing the links between genes and phenotypes, based on the variation in expression rather than in sequence. Alterations in gene expression patterns can have profound effects on biological functions of the organisms, and in fact are at the core of altered physiologic and pathologic processes. Biologists have long recognized the importance of gene regulation for a complete understanding of its functional role. DNA sequencing has permitted the initial genomic surveys counting the occurrences of sequences representing each tran-