In one technique, a transposable element called Ty1 is inserted into many genes within the DNA of yeast, thereby mutating the genes and blocking the expression of their product. Yeast with these mutations are then grown along with normal yeast in various environmental conditions. Yeast populations with mutations in one or more genes that play a key role in fitness will begin to die out. Scientists analyze populations at intervals are then able to assess what percentage of the genes on a particular chromosome are involved in various survival processes. In another technique recently developed, the mRNAs of a cell are sorted and labeled and then allowed to bind to different gene fragments. These developments will allow scientists to address many more questions and those of more complex gene expression issues.
Source: "From Genes to Genome Biology" by Elizabeth Pennisi, Science, June 21, 1996