The first trick of our trade:Mutants !Geneticists tinker with a biological process the same way a mechanically inclined child figures out the workings of an alarm clock: break it, find out what broke, take it apart, and try putting it back together to make it work. We "break" biological processes by mutating them--introducing mistakes in the genetic instructions, which cause the process to malfunction. Then we figure out where in the instructions the mistake is, and examine exactly what processes have gone awry as a result of the mutation. To prove that the mutation in question is the cause of the defect, we can try to correct the defect by introducing an intact version of the gene we suspect is broken in the mutant. Since our laboratory is interested in how sperm cells are made, we look for mutations that render worms unable to make normal sperm, causing them to be sterile. But, you may be wondering, if our mutants are sterile, how can we propagate them so we can study them? And how do we know our mutation affects sperm production, rather than egg production, or some other reproductive process, such as mating behavior? That's where C. elegans comes in handy. C. elegans comes in two sexes: male and hermaphrodite. Hermaphrodites produce both eggs and sperm, while males make only sperm. Individual hermaphrodites fertilize their own eggs with their own sperm (hermaphrodites can't mate with each other). But a hermaphrodite has the option of having its eggs fertilized by the sperm of a male with whom she has mated. If a hermaphrodite mutant is sterile when kept isolated from any males, but becomes fertile after mating to a "wild-type" (healthy) male, then her mutation must affect sperm production. Furthermore, all of the progeny from this mating contain a copy of the mutant gene that they inherited from their mutant hermaphrodite mother. Our laboratory and others have used this approach to identify and study many of the genes that affect spermatogenesis in C. elegans. Want to learn more?
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Last Modified: August 10, 2001
Paul Muhlrad pmuhlrad@u.arizona.edu