What is enhancer trapping? How does enhancer trapping work?
The P-element construct has its own promoter for a reporter gene, like lacZ or GFP. But the promoter will not express (or only very weakly) unless it comes under the control of an enhancer. You inject your reporter construct into fly embryos, it randomly integrates into the genome, and then you look for an interesting expression pattern. The P-element does not need to land really very near the enhancer or in any certain orientation, since enhancers can be long range and do not (usually) have orientation. Enhancer traps are very useful to use as markers for a certain cell type(s), so you can use them to monitor whether a cell type is affected in your mutant, without having to depend on morphological characteristics. Sometimes an enhancer trap will both interrupt a gene, creating the mutant phenotype you are trying to dissect, and be expressed in the same tissues, so that will basically tell you both the function of the gene and where its expressed. Once the enhancer that has been “trapp
