Model organism

A model organism is a non-human species used for extensive biological study. Scientists study these specific species to understand complex biological phenomena. The goal is to use discoveries made in the model to gain insight into other organisms. This strategy is possible because of common descent among all living things. Evolution has conserved many metabolic pathways and genetic material across different species.

Using these models is essential for researching human diseases. It provides a way to study illness when human experimentation is unfeasible or unethical. This approach allows researchers to understand disease processes without risking human harm.

Researchers select model organisms based on specific biological characteristics. A primary goal is finding a species that reacts to a disease similarly to human physiology. Scientists often look for organisms that are amenable to experimental manipulation. This includes having a short life-cycle to observe many generations quickly. Many models are chosen because they are easy to maintain in a laboratory setting. Some organisms are selected because their genome is compact or easy to sequence.

This makes it easier to study gene structure and regulation.

Disease models are categorized into three distinct types based on their relationship to humans. Homologous animals are those that share the same causes, symptoms, and treatment options as humans with the same disease. Isomorphic animals are different because they only share the same symptoms and treatments. Predictive models are the most distinct group. They may only be similar to a human disease in a few specific aspects. However, they are still useful for isolating and predicting the mechanisms of certain disease features.

Biological research using animal models has a very long history. The practice dates back to ancient Greece with thinkers like Aristotle and Erasistratus. In the 18th and 19th centuries, researchers made major breakthroughs using animals. Antoine Lavoisier used a guinea pig in a calorimeter to prove respiration is a form of combustion. In the 1880s, Louis Pasteur used sheep to demonstrate the germ theory of disease via anthrax.

From 1910 to 1927, Thomas Hunt Morgan used the fruit fly Drosophila melanogaster to identify chromosomes as the vector of inheritance for genes. His work helped transform biology into an experimental science.

These studies have led to massive medical achievements and specific life-saving treatments. In the late 19th century, Emil von Behring used guinea pigs to develop a diphtheria antitoxin. In 1922, research involving dogs helped lead to the discovery of insulin for treating diabetes. In the 1940s, Jonas Salk used rhesus monkey studies to isolate virulent forms of the polio virus. The resulting vaccine, available in 1955, reduced polio incidence in the United States by 15-fold in five years. Albert Sabin later improved the vaccine using animal hosts, including monkeys, for mass consumption in 1963.

Many different types of organisms serve as models across the three domains of life. The bacterium Escherichia coli is a famous model for molecular biology and lives in the human digestive system. Saccharomyces cerevisiae, or baker's yeast, is a heavily studied eukaryotic model for cell biology. The fruit fly Drosophila melanogaster remains a primary eukaryotic model for genetics. The mouse, Mus musculus, is associated with many major 20th and 21st-century discoveries. Other examples include the flowering plant Arabidopsis thaliana and the protist T. brucei.

Even viruses, such as the T4 phage, are used as models.

Model organism research connects to many different fields of science and medicine. It provides the basic knowledge required for human physiology, biochemistry, and neuroscience. Research has contributed to the development of antibiotics, the heart-lung machine, and organ transplantation techniques. Modern general anesthetics like halothane were also developed through these studies. Today, animal experimentation continues to target complex problems like Alzheimer's disease and AIDS. It is especially vital when no useful in vitro model system is available to study a condition.