Health Economics is tighted with advances in modern reserach in biology, microbiology and molecular medicine. It involves billions of dollares every moth around the world. The ultimate aim of molecular medicine is to understand human physiology at the molecular level and to apply this knowledge in curing disease. The complete sequence of the human genome is now known, but researchers have little idea of what the products of most of these genes actually do. Since direct experimentation with humans is greatly RESTRICTED, animal models are necessary. And yes, I am in favor of animal test before human tests.
Although a range of animals has been used to investigate various topics, the rat and the mouse are the most widespread laboratory animals. Rats were favored in the early days of biochemistry when metabolic reactions were being characterized. Mice are smaller and breed faster than rats, and are easier to modify genetically. Consequently, the mouse is used more often for experiments involving genetics and molecular biology. Mice live from 1 to 3 years and become sexually mature after about 4 weeks. Pregnancy lasts about three weeks and may result in up to 10 offspring per birth.
Humans have two copies each of approximately 20,000–25,000 genes scattered over 23 pairs of chromosomes. Mice have a similar genome, of 2,600 Mb of DNA carried on 20 pairs of chromosomes. Less than 1% of mouse genes lack a homolog in the human genome. The average mouse (or human) gene extends over 40 kilobases of DNA that consists mostly of non-coding introns (approximately seven per gene). Nowadays there are many strains of mutant mice in which one or more particular genes have been altered or disrupted. These are used to investigate gene function.
Intact humans cannot be used for routine experiments for ethical reasons. However, it is possible to grow cells from both humans and other mammals in culture. Many cell lines from humans and monkeys are now available. Such cells are much more difficult to culture than genuine single-celled organisms. Cell lines from multicellular organisms allow fundamental investigations into the genome and other cell components. Historically, the most commonly-used cell lines (e.g., HeLa cells) are actually cancer cells. Unlike cells that retain normal growth regulation, cancer cells are “immortalized,” that is they are not limited to a fixed number of generations. In addition, cancer cell lines can often divide in culture in the absence of the complex growth factors needed to permit the division of normal cells.