What are Model Organisms?
The term 'model organism' refers to any species that is used by scientists for research purposes. [1] These organisms are chosen because they possess some quality that makes them ideal for research-- they frequently have short generation times, produce large quantities of offspring, or possess similar genes or physiology to humans. [2] In addition, because they are so often used by researchers, there is a large body of prior research to consult when utilizing a common model organism. [3] The most popular model organisms have fully-sequenced genomes, and large databases have been compiled of their genes and gene products. [3]
Common Model Organisms
Mus musculus - House Mouse
Of the most popular model organisms, mice most closely model the human genome and human physiology. [3] For that reason, they are often used in medical research. Despite having relatively long generational times and expensive upkeep costs, there is a vast body of research detailing the mouse genome and phenotypes. [4]
Danio rerio - Zebrafish
Zebrafish breed more easily and rapidly than mice, are cheaper to maintain, and partially transparent, making them ideal for modelling phenotypes that would otherwise require dissection to view. [4] Zebrafish are also frequently used to model embryonic development, as their clear eggs grow outside the mother. [4]
Xenopus tropicalis - Western Clawed Frog
The western clawed frog is often used as a model for embryonic and early life development, as they produce thousands of eggs per generation. [5] These eggs develop externally and are relatively large, so they are easily observed. [5] The major disadvantage to this model organism is their genomic dissimilarity to humans, compared to other organisms used to model early development. [5]
Drosophila melanogaster - Fruit Fly
Drosophila are among the most popular research organisms, owing to their very fast generational cycles, small genome, and easily-observable mutations. [3] They are a relatively old model organism, and there is a well-established body of literature to draw from when using them as a model. A major downside to using Drosophila as a model organism is how different they are anatomically from humans. [3] However, much of their neurological physiology is similar to humans', so they are a good model for neurological and neurodevelopmental research. [4]
Caenorhabditis elegans - Nematode
C. elegans is unique as a model organism, in that the developmental of every cell in its body has been mapped from embryo to mature specimen, making it an excellent organism to study embryonic development. [3] Additionally, owing to their extremely simple anatomy, they have rapid generational cycles, are cheap and easy to maintain, and are easy to manipulate. [4] C. elegans shares the disadvantage common to very small model organisms-- anatomically, they are fairly dissimilar to humans, which limits their research applications. [4]
Conclusion
For the study of GLI3 and its relation to polydactyly, mus musculus will be utilized as a model organism. A suitable model organism must be capable of displaying a polydactl phenotype. In other words, the model organism must have legs or homologous appendages. This limits the pool of available model organisms already. Further research indicates that of the remaining model candidates, only Mus musculus has an established body of research detailing polydactyly phenotypes.
Protein homology research also indicates that human's GLI3 protein is far more conserved within vertebrates, which makes using Drosophila melanogaster a potentially risky move, as its limb determination mechanism is not as likely to resemble a human's as a mouse's limb/digit determination mechanism is.
Protein homology research also indicates that human's GLI3 protein is far more conserved within vertebrates, which makes using Drosophila melanogaster a potentially risky move, as its limb determination mechanism is not as likely to resemble a human's as a mouse's limb/digit determination mechanism is.
References
- Wellcome Genome Campus. (March 2017). What are model organisms? Retrieved from https://www.yourgenome.org/facts/what-are-model-organisms
- NIGMS. (October 2017). Using Research Organisms to Study Health and Disease. Retrieved from https://www.nigms.nih.gov/education/Pages/modelorg_factsheet.aspx
- Murphy, P. (n.d). Lecture 2: Model organisms. Retrieved from http://virtuallaboratory.colorado.edu/DEVO@CU/papers/pmby1101-lecture2-2013.pdf
- University of Iowa Department of Biology. (November 2014). Model Organisms. Retrieved from https://biology.uiowa.edu/model-organisms
- Understanding Animal Research. (February 2018). Frogs (Xenopus) in medical research. Retrieved from http://www.understandinganimalresearch.org.uk/resources/video-library/frogs-xenopus-in-medical-research/
Images
Header: https://www.latimes.com/opinion/readersreact/la-ol-le-female-mice-lab-research-20190605-story.html
Image 1: https://www.irishtimes.com/news/science/of-mice-and-medicine-the-ethics-of-animal-research-1.2529740
Image 2: https://www.deccanherald.com/spectrum/science/zebrafish-emerging-research-model-671035.html
Image 3: https://www.eurekalert.org/multimedia/pub/125300.php
Image 4: https://www.discovermagazine.com/planet-earth/fruit-fly-study-questions-the-assumption-that-brains-need-sleep
Image 5: https://www.apsnet.org/edcenter/apsnetfeatures/Pages/Celegans.aspx
Image 1: https://www.irishtimes.com/news/science/of-mice-and-medicine-the-ethics-of-animal-research-1.2529740
Image 2: https://www.deccanherald.com/spectrum/science/zebrafish-emerging-research-model-671035.html
Image 3: https://www.eurekalert.org/multimedia/pub/125300.php
Image 4: https://www.discovermagazine.com/planet-earth/fruit-fly-study-questions-the-assumption-that-brains-need-sleep
Image 5: https://www.apsnet.org/edcenter/apsnetfeatures/Pages/Celegans.aspx
This web page was produced as an assignment for Genetics 564, an undergraduate capstone course at UW-Madison.