Model Organisms

Besides certain primates (such as monkeys and chimpanzees), which are costly and difficult to rear in the laboratory, the model organism most closely related to humans is the mouse, Mus musculus. The mouse genome is about the same size as the human genome, and the organization of genes (the order of genes on chromosomes) is strikingly similar between the two species. Findings from the nearly complete mouse genome sequencing project indicate that mice and humans share about 95 percent DNA sequence similarity. This means that any gene in humans is likely to have an identical or very similar counterpart (homologue) in the mouse genome.

In addition, it is much easier and less expensive to study genes in mice. A technology that has made the mouse an invaluable genetic model system is the ability to engineer "knockout" strains. These are mutant strains in which a single known gene has been selectively deleted from the genome of every cell. For human genes implicated in diseases, knocking out the homologous gene in mice can provide an excellent model system for studying the disease. The knockout mouse may show disease conditions similar to those of the human disease. Learning how the elimination of the gene in the mouse contributes to the mouse disease may then give important clues about the involvement of the homologous gene in the human disease. "Disease model" mouse strains are available for such disorders as cancer, Alzheimer's disease, arthritis, diabetes, heart disease, cystic fibrosis, and obesity.