 The disadvantage is that at least three independent insertion sites are required, so the lines must use different and independent insertion sites, and creating the desired final organisms needs more than a single cross.This is a very active field of research, and there are many such intersectional strategies, of which two are discussed below.One way to create GAL4 expression in the cells that are in line A but not line B, requires line A to be made to express GAL4, and line B made to express Gal80, which is a GAL4 inhibitor.