Model organism

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Electron micrograph of several E. coli cells
Drosophila, one of the most famous subjects for experiments

A model organism is a species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. In particular, model organisms are widely used to explore potential causes and treatments for human disease when human experimentation would be unfeasible or unethical. This strategy is made possible by the common descent of all living organisms, and the conservation of metabolic and developmental pathways and genetic material over the course of evolution.[1]

Selecting a model organism

Often, model organisms are chosen on the basis that they are amenable to experimental manipulation. This usually will include characteristics such as short life-cycle, techniques for genetic manipulation (inbred strains, stem cell lines, and transfection systems) and non-specialist living requirements. Sometimes, the genome arrangement facilitates the sequencing of the model organism's genome, for example, by being very compact or having a low proportion of junk DNA (e.g. yeast, Arabidopsis, or pufferfish).

When researchers look for an organism to use in their studies, they look for several traits. Among these are size, generation time, accessibility, manipulation, genetics, conservation of mechanisms, and potential economic benefit. As comparative molecular biology has become more common, some researchers have sought model organisms from a wider assortment of lineages on the tree of life.

Use of model organisms

There are many model organisms. One of the first model systems for molecular biology was the bacterium Escherichia coli, a common constituent of the human digestive system. Several of the bacterial viruses (bacteriophage) that infect E. coli also have been very useful for the study of gene structure and gene regulation (e.g. phages Lambda and T4). However, bacteriophages are not organisms because they lack metabolism and depend on functions of the host cells for propagation.

In eukaryotes, several yeasts, particularly Saccharomyces cerevisiae ("baker's" or "budding" yeast), have been widely used in genetics and cell biology, largely because they are quick and easy to grow. The cell cycle in a simple yeast is very similar to the cell cycle in humans and is regulated by homologous proteins. The fruit fly Drosophila melanogaster is studied, again, because it is easy to grow for an animal, has various visible congenital traits and has a polytene (giant) chromosome in its salivary glands that can be examined under a light microscope. The roundworm Caenorhabditis elegans is studied because it has very defined development patterns involving fixed numbers of cells, and it can be rapidly assayed for abnormalities.

Electron microphotograph of tobacco mosaic virus (TMV) particles

Important model organisms


Viruses include:


Sporulating Bacillus subtilis

Prokaryotes include:


Eukaryotes include:





  • Cavia porcellus, the guinea pig, used by Robert Koch and other early bacteriologists as a host for bacterial infections, hence a byword for "laboratory animal" even though less commonly used today
  • Chicken (Gallus gallus domesticus) - used for developmental studies, as it is an amniote and excellent for micromanipulation (e.g. tissue grafting) and over-expression of gene products
  • Cat (Felis cattus) - used in neurophysiological research
  • Dog (Canis lupus familiaris) - an important respiratory and cardiovascular model
  • Hamster - first used to study kala-azar (leishmaniasis)
  • Mouse (Mus musculus) - the classic model vertebrate. Many inbred strains exist, as well as lines selected for particular traits, often of medical interest, e.g. body size, obesity, muscularity. (Quantitative genetics, Molecular evolution, Genomics)
  • Homo sapiens (humans) - used in various clinical studies
  • Oryzias latipes, Medaka (the Japanese ricefish) is an important model in developmental biology, and has the advantage of being much sturdier than the traditional Zebrafish
  • Rat (Rattus norvegicus) - particularly useful as a toxicology model; also particularly useful as a neurological model and source of primary cell cultures, owing to the larger size of organs and suborganellar structures relative to the mouse. (Molecular evolution, Genomics)
  • Rhesus macaque - used for studies on infectious disease and cognition
  • Sigmodon hispidus - Cotton rat formerly used in polio research
  • Taeniopygia guttata or zebra finch - used in the study of the song system of songbirds and the study of non-mammalian auditory systems
  • Takifugu rubripres, a pufferfish - has a small genome with little junk DNA
  • Xenopus laevis, the African clawed frog - used in developmental biology because of its large embryos and high tolerance for physical and pharmacological manipulation
  • Zebrafish (Danio rerio), a freshwater fish, has a nearly transparent body during early development, which provides unique visual access to the animal's internal anatomy. Zebrafish are used to study development, toxicology and toxicopathology[9], specific gene function and roles of signaling pathways.

Model organisms used for specific research objectives

Sexual selection and sexual conflict

Hybrid zones


  1. Fox, Michael Allen (1986). The Case for Animal Experimention: An Evolutionary and Ethical Perspective. Berkeley and Los Angeles, California: University of California Press. ISBN 0-520-05501-2.
  2. Chlamydomonas reinhardtii resources at the Joint Genome Institute
  3. Chlamydomonas genome sequenced published in Science, October 12, 2007
  4. Rowland H. Davis: Neurospora. Contributions of a Model Organism. Oxford University Press, Oxford, 2000. ISBN 0-19-512236-4.
  5. 5.0 5.1 5.2 5.3 About Arabidopsis on the The Arabidopsis Information Resource page (TAIR)
  6. 6.0 6.1 Rensing, S. A., Lang, D., Zimmer, A. D., Terry, A., Salamov, A., Shapiro, H. et al. (2008). The physcomitrella genome reveals evolutionary insights into the conquest of land by plants. Science, 319(5859), 64-69.
  7. Riddle, Donald L.; Blumenthal, Thomas; Meyer, Barbara J.; and Priess, James R. (Eds.). (1997). C. ELEGANS II. Woodbury, NY: Cold Spring Harbor Press. ISBN 0-87969-532-3. Full text available on-line.
  8. Manev H, Dimitrijevic N, Dzitoyeva S. (2003). "Techniques: fruit flies as models for neuropharmacological research". Trends Pharmacol. Sci. 24 (1): 41–43.
  9. Spitsbergen J.M. and Kent M.L. (2003). The state of the art of the zebrafish model for toxicology and toxicologic pathology research--advantages and current limitations. Toxicol Pathol. 31 (Supplement), 62-87. PubMed Abstract Link => PMID 12597434.

See also

External links

cs:Modelový organismus de:Modellorganismus id:Organisme model it:Organismo modello he:אורגניזם מודל la:Instar animans nl:Modelorganisme nn:Modellorganisme uk:Модельний організм