Functional Analysis of Mutants

A model organism is a non-human species that can be studied to understand particular biological phenomena. Some common examples of model organisms are the microscopic nematode C. elegans, the fruit fly Drosophila melanogaster, and the mouse. They serve as good substitutes when it isn’t possible or practical to study humans directly.

While scientists have made tremendous strides in uncovering how the cells of our bodies function, there is still much more to be learned. Having a thorough understanding of cellular processes can lead to the development of better therapeutics or preventative interventions, but it can be really difficult to understand how those therapies work in humans. We do have some pretty good tools for studying human cells, but when it comes to understanding how different body systems interact, how a drug impacts different tissues, or how DNA and RNA function, scientists often turn to model organisms for help.

A model organism is a non-human species that can be studied to understand particular biological phenomena. The expectation is that we can take the knowledge we gain by studying a model organism and then apply it to humans. Some common examples of model organisms are mice, fruit flies (or Drosophila melanogaster), and microscopic worms called C. elegans. It might seem like these organisms are nothing like humans, but they actually have very similar biological features (such as their DNA), so they serve as good substitutes when it isn’t possible or practical to study humans directly. These organisms are ideal because they often take less time to mature than humans, are less expensive to study, take up a small amount of space, and are easy to alter at a genetic level. By changing the genetic information of an organism, you create a mutant version of that organism, and mutants are one of the most powerful tools in a scientist’s toolkit.

As you know, DNA is the critically important instruction manual that regulates the function and phenotype of cells in our bodies. DNA serves as a template from which RNA and proteins can be synthesized. If the DNA becomes changed or mutated in certain ways, this can potentially cause disease by altering (or completely eliminating) the formation of proteins. While this sounds really bad, scientists can actually use mutations to their advantage to discover the function of certain genes or proteins within cells. Let’s take a look at how that might work conceptually.

Imagine we take a trip to a factory that produces cars. On the first day of our visit, we see a group of workers enter the factory in the morning, and completed, fully-functioning cars coming out of the factory in the afternoon. This day serves as our reference point for how the factory normally functions. On the second day, we learn that one of the workers has called in sick and won’t be coming to work that day. That afternoon, cars come out of the factory, but are missing their front windshields. This allows us to infer that the worker who called in sick was responsible for adding the front windshields to the cars. The absence of his job being performed resulted in a defective car. On the third day of our visit, the sick worker is back but a different worker has hurt their hand and is unable to perform their normal tasks. We now observe cars coming out of the factory that are missing both of the left side doors. We can now infer that this worker’s job was to add doors on the left side of the car. By observing what happened to the cars in the absence of different workers, we were able to infer what role those individuals played in the production process.

Mutant analysis is attempting to do the same thing. However, instead of absent workers and defective products, scientists study mutants and observe mutant phenotypes. Let’s say a group of researchers are using Drosophila to understand the function of a newly discovered gene. Let’s call it Gene A. Since they have no idea what Gene A does, they decide to generate flies with a mutation in Gene A. I won’t get into the specifics of how they did this, but the result is that the mutant flies lack Gene A function similar to how the factory lacked the missing worker’s job function. Normally, wild-type flies have red eyes. However, upon studying the mutant flies, the scientists noticed that the eyes of these flies are white. If we use the same rationale we applied to the factory worker jobs, without Gene A function, the red pigment is absent and a white eye phenotype is the result. Thus, we can infer that Gene A plays a necessary role in producing the red eye pigment. Scientists have been analyzing mutants in model organisms for decades to gain a better understanding of how genes function. The results of these studies have provided insight into human biology and the progression of many diseases.

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