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Genetics in the lab
How do we use genetics in the lab? Genetic tools are extremely important to laboratory research in many fields. Cancer, bacteriology, virology, and immunology are some fields that make extensive use of genetics tools in research. In short, geneticists manipulate the genes of an organism by deleting, adding, or changing DNA sequence from or to an organism's genome. We make observations on how the mutations affect the organism's behavior. We then draw conclusions based on what we observe.
Why do we make mutants? As stated above, in the lab we can remove, add, or change genes in a wide variety of organisms, from the bacteria E. coli, to plants and mice. Once a gene has been manipulated, we work with the new mutant to answer scientific questions. Let’s go through an example to show how mutant analysis works in a genetics lab.
Why do we make mutants?We are studying the fictional bacteria B. maganoinus. We know the bacteria have “Gene X”, but we do not know what Gene X does and we want to find out. We first compare the DNA sequence of Gene X to other genes of which we know the function. If we find an exact or very close match we can guess that Gene X does the same thing as the other gene. We can then do some quick experiments to confirm it has the same function. However, if our DNA sequence search does not turn up a close match, we will delete Gene X and observe the mutant’s behavior to learn the function of Gene X.
Why do we make mutants?So we have now made a mutant strain that lacks Gene X. Let’s look at some easy experiments we can do to begin to determine the role of Gene X. We know our bacteria can eat four foods A, B, C, and D. Let’s grow our mutant each of these foods to see if it still has the ability to use it. If it loses the ability to grow on one of the foods we can conclude Gene X is somehow important for using that food. We will grow it on agar plates and in liquid culture in a tube.
Why do we make mutants?The mutant bacteria seem to grow fine on each of the four foods we used in this experiment, both on agar plates and in liquid culture. Let’s go home for the night and think about it.
Why do we make mutants? Uh oh! Last night the sloppy grad student forgot to clean up yesterday’s experiment. But wait, look what happened in the liquid culture that sat out on the bench overnight! All of the tubes with the mutant have cleared and all of the bacteria appear to be in a pile on the bottom of the tube. All of the wildtype bacteria still have somewhat cloudy media. A PHENOTYPE!!! In this type of genetic analysis a phenotype is the first step to understanding a gene’s function. Here we have an observable difference between the mutant and wildtype bacteria (phenotype) that will help us discover the function of Gene X.
Why do we make mutants?This phenotype sounds like bacteria that can’t swim, or are non-motile. Let’s look at some bacteria under the microscope. First we’ll look at the wildtype bacteria. They are darting all over the field in the microscope. When we look at the mutant, they are just twitching a little.
Why do we make mutants?Let’s take a closer look on the electron microscope. We fix some of each strain of bacteria. And place them on the electron microscope, which can see much smaller details than the light microscope. The wildtype bacteria seem to have long spiral hairs (flagellin) coming from each cell. The mutant is missing Aha! Gene X is important for making flagellin. We don’t know what Gene X does exactly, but we now have a good idea of what it is important for.
Why do we make mutants?For a better understanding of lab genetics, here is an excellent analogy entitled “The Salvation of Doug”, written by a professor of genetics at the University of California, Santa Cruz, Dr. William Sullivan (no relation). He describes how a geneticist would go about figuring out how a car is made using tools analogous to those used in the genetics lab.
About the site: I developed as a companion website to Everything a cell does is a direct result of the genetics of that cell, whether it is a single-cell organism or part of a much larger organism. Thus, understanding the cells requires an understanding of the basis of all of their behaviors. About the author: I am a microbiologist studying microbial pathogenesis and the host immune response. My studies have included work in many pathogens including Rabies and Influenza viruses, Mycobacterium tuberculosis, Francisella tularensis, and Salmonella enterica. I currently live just outside of Philadelphia, PA, where I work as a postdoctoral fellow researching antigen processing and presentation during rabies infection. My email is always open for suggestions, corrections, or any other comments. Please feel free to contact me: