Question

when a horse and donkey mate they produce a mule, which is infertile, meaning it cannot produce offspring itself. this is an example of which of the following?
prezygotic barrier
gametic isolation
postzygotic barrier

Explanation:

• Prezygotic barrier: Prevents fertilization before zygote formation. Examples include habitat, temporal, behavioral, mechanical, or gametic isolation. Since the horse and donkey have already mated and produced a zygote (the mule), this is not a prezygotic barrier.
• Gametic isolation: A type of prezygotic barrier where gametes (sperm and egg) from different species cannot fuse. Again, since a zygote (the mule) has formed, this is not gametic isolation.
• Postzygotic barrier: Occurs after fertilization (zygote formation). It includes reduced hybrid viability (the hybrid has low survival rate), reduced hybrid fertility (the hybrid is sterile like the mule), or hybrid breakdown (the offspring of hybrids have problems). The mule is sterile, which fits the definition of a postzygotic barrier (reduced hybrid fertility).

Answer:

postzygotic barrier