As we have seen, genetic analysis is a powerful method for investigating the properties of genes. By studying the inheritance of genetic traits, Mendel was able to elucidate the particulate nature of hereditary factors and deduce the laws of equal segregation and independent assortment.
When Mendel performed his genetic crosses, he wasn't particularly interested in the nature of the contrasting traits he was using to study the mechanisms of inheritance. Rather, these traits were simply genetic markers that allowed him to follow the inheritance of the corresponding genes.
In contrast to Mendel's studies, the phenotype of the genetic variants (or mutants) is of central interest with genetic dissection. This form of genetic analysis is an unparalleled method for investigating unexplored biological processes. By finding mutations that specifically disrupt a biological process, one can thereby identify genes required for that process. For example, biologists interested in how a cell decides when to enter mitosis have isolated many mutations which disrupt a cell's normal progression through the cell cycle. By studying the nature of these genes, biologists have been able to further characterize the cellular machinery required for the regulation of the cell cycle.
In this multi-week laboratory investigation, we will consider genetic dissection using the nematode C. elegans, or the "worm", as it is affectionately called. This "model organism" has become popular for studying complex biological processes found in animals, such as development and neurobehavior. The first step in genetic dissection is to screen for mutants perturbing the biological process being studied; for example, mutants that fail to move properly. These mutants can then be characterized genetically, for example, to determine how many different genes are mutated, and molecularly, for example, to deduce the structure and function of the encoded protein. Subsequently, one can identify additional genes required for the process under study by screening for suppressors of the initial mutations.
After being introduced to C. elegans, you will be given an uncoordinated mutant strain that has been exposed to a mutagen. Your objective is to identify suppressor mutations that restore wild-type movement, characterize the nature of this secondary mutation, and then determine if it is linked to the primary, uncoordinated mutation. Finally, you will propose experiments to determine if the new mutation is allelic to previous suppressor mutations.
Bio 306 Genetics HyperText Lab Manual
William R. Morgan wmorgan@acs.wooster.edu