Model organism

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Drosophila melanogaster, one of the most famous subjects for experiments

A model organism is a non-human 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.[1] Model organisms are in vivo models and are widely used to research human disease when human experimentation would be unfeasible or unethical.[2] 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.[3] Studying model organisms can be informative, but care must be taken when extrapolating from one organism to another.

Selecting a model organism[edit]

Models are those organisms with a wealth of biological data that make them attractive to study as examples for other species and/or natural phenomena that are more difficult to study directly. Continual research on these organisms focus on a wide variety of experimental techniques and goals from many different levels of biology—from ecology, behavior, and biomechanics, down to the tiny functional scale of individual tissues, organelles, and proteins. Inquiries about the DNA of organisms are classed as genetic models (with short generation times, such as the fruitfly and nematode worm), experimental models, and genomic parsimony models, investigating pivotal position in the evolutionary tree.[4] Historically, model organisms include a handful of species with extensive genomic research data, such as the NIH model organisms.[5]

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 methods of transformation) 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[edit]

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[edit]

Viruses[edit]

Viruses include:

Prokaryotes[edit]

Sporulating Bacillus subtilis

Prokaryotes include:

Eukaryotes[edit]

Eukaryotes include:

Protists[edit]

Fungi[edit]

Plants[edit]

Animals[edit]

Main article: Animal model
Invertebrates[edit]
Vertebrates[edit]
Laboratory mice
  • Cat (Felis sylvestris catus) - used in neurophysiological research.
  • 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.
  • Cotton rat (Sigmodon hispidus) - formerly used in polio research.
  • Dog (Canis lupus familiaris) - an important respiratory and cardiovascular model, also contributed to the discovery of classical conditioning.
  • Golden hamster (Mesocricetus auratus) - first used to study kala-azar (leishmaniasis).
  • Guinea pig (Cavia porcellus) - 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.
  • Medaka (Oryzias latipes, or Japanese ricefish) - an important model in developmental biology, and has the advantage of being much sturdier than the traditional Zebrafish.
  • 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, voluntary wheel-running behavior.[39] (Quantitative genetics, Molecular evolution, Genomics)
  • 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 (or Rhesus monkey) (Macaca mulatta) - used for studies on infectious disease and cognition.
  • Sea lamprey (Petromyzon marinus) - spinal cord research
  • Takifugu (Takifugu rubripes, a pufferfish) - has a small genome with little junk DNA.
  • Xenopus tropicalis and Xenopus laevis (African clawed frog) - eggs and embryos from these frogs are used in developmental biology, cell biology, toxicology, and neuroscience[40][41]
  • Zebra finch (Taeniopygia guttata) - used in the study of the song system of songbirds and the study of non-mammalian auditory systems.
  • 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,[42] specific gene function and roles of signaling pathways.


Model organisms used for specific research objectives[edit]

Sexual selection and sexual conflict[edit]

Hybrid zones[edit]

  • Bombina bombina and variegata
  • Podisma spp. in the Alps
  • Caledia captiva (Orthoptera) in eastern Australia

Ecological genomics[edit]

Table of model genetic organisms[edit]

This table indicates the status of the genome sequencing project for each organism.

Organism Genome Sequenced
Prokaryote
Escherichia coli Yes
Eukaryote, unicellular
Dictyostelium discoideum Yes
Saccharomyces cerevisiae Yes
Schizosaccharomyces pombe Yes
Chlamydomonas reinhardtii Yes
Tetrahymena thermophila Yes
Emiliania huxleyi Yes
Eukaryote, multicellular
Caenorhabditis elegans Yes
Drosophila melanogaster Yes
Arabidopsis thaliana Yes
Physcomitrella patens Yes
Vertebrate
Danio rerio Yes
Mus musculus Yes
Xenopus laevis (Note: and X. tropicalis)[43] Yes
Homo sapiens (Note:not a model organism) Yes

See also[edit]

References[edit]

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External links[edit]