Holt Modern Biology 1st Edition by John Postlethwait ,Janet Hopson

Exercise 5

DIRECTIONS: Choose the letter of the answer choice that best answers the question. Saint Bernards and Chihuahuas (two breeds of domestic dogs) cannot normally mate because they differ so much in size. Thus, they are reproductively isolated to some extent. What type of isolating mechanism is operating in this case?
F) artificial
G) prezygotic
H) postzygotic
J) geographic