Gene expression patterns can be used to test hypotheses based on morphology. For example, the regulatory gene Bapx1 is expressed in the hinge of the developing lower jaw in fishes and reptiles. Where would you predict Bapx1 expression to occur in mammals? A. in the developing cheekbone
B. in the developing lower jaw
C. in the mature lower jaw
D. in the developing ear bones

The correct answer is option D. "in the developing ear bones".

Explanation:

The developing lower jaw of fishes and reptiles has a variety of bones that are joined together, forming the mandible that they use to eat their preys. Some bones in the developing lower jaw of fishes and reptiles are equivalent to the developing ear bones of mammals. Therefore we can predict that the Bapx1 expression in mammals will occur in the developing ear bones. About this evolutionary relationship, scientist Zhe-Xi Luo of the Carnegie Museum of Natural History in Pittsburgh states "Reptiles have [a] jaw full of ear bones from mammals and mammals have an ear full of jawbones of reptiles".

c should be the answer