Practice Test 6

In a vertebrate group, embryos of Species M and Species N both develop pharyngeal arches and a post-anal tail during early stages. In later development, Species M retains a tail and forms gill structures, while Species N loses the tail and develops middle-ear bones. Genetic analysis shows both species share highly similar sequences in a conserved developmental gene that regulates arch formation. Which conclusion is best supported by the embryological and molecular evidence?

Initial reaction rates are measured at multiple substrate concentrations for an enzyme with and without Inhibitor Z. With Z present, the maximum rate observed at very high substrate concentration is lower than without Z, and increasing substrate does not restore the original maximum. Enzyme concentration, pH, and temperature are constant. Which explanation best accounts for Inhibitor Z’s effect?​