All of the homeotic genes in Drosophila have been cloned. As discussed in Chapter 20, cloned genes can be manipulated in vitro. They can be subjected to cutting and pasting, site-directed mutagenesis, etc. After Drosophila genes have been altered in vitro, they can be inserted into a Drosophila transposon vector (i.e., a P element vector), and then the altered gene within a P element can be injected into Drosophila embryos. The P element then transposes into the chromosomes, thereby introducing one or more copies of the altered gene into the Drosophila genome. This method is termed P element transformation.
With these ideas in mind, how would you make a mutant gene with a gain of function in which the Antp gene would be expressed where the abd-A gene is normally expressed? What phenotype would you expect for flies that carried this altered gene?