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By Sara McPherson
Genetics is the study of traits that are passed down from generation to generation. These traits can include physical traits such as hair colour and height or may involve less understood traits like the risk for certain diseases. The bases of these factors are found in each person’s DNA— the blueprint of life for all organisms, from single-celled bacteria to the biggest animals on earth. DNA is the foundation of what makes all humans the same and what makes each person unique. Although there has been a lot of research on these areas, there is still much to be uncovered about human genetics and systems found in the body.
Genetics, particularly human genetics, is a complex and highly studied area of research. It is very important in studying things like diseases and understanding how cells work in our bodies. Without this understanding, it becomes nearly impossible to find effective treatments and cures for even the simplest of infections. Humans are particularly hard to understand because of how big and complex they are, and people live too long to fully understand genetics at each life stage. It is so much easier to look at single-celled organisms like the bacteria E. coli, which mate and generate new cells in a matter of hours. Not only is this generation time very fast, but the small amount of DNA within each cell makes it easier to study. Scientists are always looking at more efficient ways to study human biology. One of the ways they do this is by looking at model organisms.
But what are model organisms?
Model organisms are species that are highly studied by scientists, meaning they are well known and their biology is understood in depth. For example, C. elegans (a microscopic worm) is so well understood that scientists know the order in which each cell will grow throughout its lifetime. Model organisms are often chosen in research because they are small, cost-effective, can easily be bred in the lab, are well understood in terms of their genetics, and may have specific human applications. Each one of these factors is important because they help with research that could not normally be performed at the human level. Some examples of well-known model organisms include bacteria, yeast, fruit flies, nematodes (a type of worm), the western clawed frog, zebrafish, and mice. All of these species have quick generation times, meaning that they are able to reproduce very fast. These species also have specific applications that make them useful in human research.
Image Source: https://elifesciences.org/articles/06956
Mice, for example, are mammals which means they can be more easily compared to humans than non-mammalian model organisms because of their functional similarities. They are particularly important for the study of human diseases because they are genetically similar to humans, can have many of the same diseases, and mice can be altered to mimic many human conditions.
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With this understanding, the study of cancer would be much easier done in mice than in yeast, even though yeast breed much faster than mice. Mice are commonly used in cancer research because mouse cells react like human cells when exposed to cancer cells and drugs used in cancer treatments. This is important because there is a need to ensure that cancer drugs will actually help treat cancer before testing them in humans. Although mice are very useful in a variety of applications, there are some issues with factors such as space when caring for mice as well as some ethical considerations with animal testing.
A simpler organism, C. elegans, is often used to better understand human disease, specifically biological problems that occur within these diseases. This worm has been studied since the 1960’s. Since its initial research, C. elegans continues to be highly studied with over a thousand publications coming out each year. Because this model organism is so well understood, there are broad spectrums of applications that still make it useful today. In terms of human disease, there are many genes that are found in C. elegans that are also found in humans. This is important because they can be studied in the worm and the research can be directly applied to human systems. Studies indicate that 40% of genes that have a known association with human diseases are also found in C. elegans. Research on these genes will help scientists better understand the diseases, thus expanding on the list of potential treatments.
Image Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2515201/
Although there are many positive applications of model organisms and irreplaceable research that has been performed, there are still concerns and potential issues with using model organisms as a means of understanding human biology. There is one issue, known as the paradox of model organisms, which shows how important these organisms have been in understanding molecular biology, but understands that not being able to study humans can cause some spectacular problems. A case of particular significance was the development of a treatment for rheumatoid arthritis. In this case, primates were one of the organisms used in testing and the results were positive enough to begin human trials for this treatment. However, when tested in humans, the treatment caused an unexpected and life-threatening immune response. In this case, the issue occurred because the lab animals were raised in a relatively sterile environment; therefore, they did not have the same reactions as humans which over their lifetimes have been exposed to a variety of pathogens and allergens. If they had been able to test on animals outside a laboratory setting, the results would have been similar to what was seen in humans. Unfortunately, these results are not always predictable.
This case shows that model organisms can be very helpful and are useful in many cases, but there are significant drawbacks to not being able to test directly on the organism of study (humans in this case). Scientists are always looking for better ways to study humans and human diseases, but there is a reason that model organisms are still used. There is simply no replacement at this time. Perhaps, at some point in the future, these will be developments that will have better options, but for now, model organisms stay as a central piece of research and a key method of understanding the complexities of biology.
- What are model organisms? [Internet]. Facts. The Public Engagement team at the Wellcome Genome Campus; 2021 [cited 2022Mar14]. Available from: https://www.yourgenome.org/facts/what-are-model-organisms
- Alfred J, Baldwin IT. The natural history of model organisms: New opportunities at the wild frontier [Internet]. eLife. eLife Sciences Publications, Ltd; 2015 [cited 2022Mar17]. Available from: https://elifesciences.org/articles/06956
- Hunter P. The paradox of model organisms. The use of model organisms in research will continue despite their shortcomings [Internet]. EMBO reports. Nature Publishing Group; 2008 [cited 2022Mar17]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2515201/
- A transparent window into biology: A primer on caenorhabditis elegans* [Internet]. WormBook Header Image. [cited 2022Mar21]. Available from: http://www.wormbook.org/chapters/www_celegansintro/celegansintro.html
- What is a mouse model? [Internet]. The Jackson Laboratory. [cited 2022Mar21]. Available from: https://www.jax.org/why-the-mouse/model#:~:text=Mice%20are%20the%20most%20commonly,any%20human%20disease%20or%20condition.
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