The genes that are controlled by the inversion process encode two alternative forms of flagellin(called the H1 and H2 forms), the protein component of the flagellar filament.Flagella are on the surface of the bacteria and are thus a common target for the immune system(Fig. 12-12).By using Hin to switch between these alternative forms, at least some individuals in the bacterialpopulation can avoid recognition of this surface structure by the immune system.