Consider that there is a recombinant DNA construct called myo$-2$::GFP that Celegans developmental

geneticists have transformed into worms. Worms containing this construct express green fluorescent

protein $($GFP$)$ in their pharynx, an organ located between the mouth and the gut that grinds up the

bacteria C$.$ elegans eats as a food source. In the myo$-2$:;GFP construct, the open reading frame for

jellyfish GFP was cloned downstream of the promoter and enhancer for myo$-2,$ a gene that is specifically

expressed in the muscle cells of the pharynx.

a$.$ Explain how you could use transgenic worms expressing the myo$-2$::GFP transgene to find mutations

that disrupt the structure of the pharynx. How would the presence of the transgene facilitate the mutant

screen?

b$.$ Suppose you wanted to determine whether a particular gene X was important for specification of the

pharynx, but mutations in this same gene disrupt embryonic development well before pharyngeal

structures appear. How could you use myo$-2$::GFP$,$ the myo$-2$ promoter, the DNA sequence of gene X$,$

and your knowledge of RNA interference $($RNAi$)$ to generate worms that lack gene X expression in the

pharynx but express gene X in all other tissues in which it is expressed in wild$-$type C$.$elegans?