In primary mutant screens, A) mutant flies are identified by morphology and then the mutant genes are isolated and studied. B) mutant flies are created by RNAi using random RNA sequences and then the genes affected identified. C) mutant flies are created by gain-of-function expression of random genes. D) two mutant flies are mated to determine if there is an effect on morphology.

The images show two species of tree frogs in a particular region. the gray tree frogs are adapted to the trees of the woodlands, while the green tree frogs can survive in woodlands or grasslands. the gray frog was abundant in the woodlands. because of climatic changes, most of the trees in the region died, and the woodlands changed to grasslands. in such a case, the . the gray tree frog is closely related to the green tree frog genetically, but they have different mating calls. this suggests that speciation occurred because of .