Question

when a lion and a tiger mate, they have offspring, but the hybrids are unable to reproduce. this is an example of what type of reproductive barrier? gametic isolation a postzygotic barrier mechanical isolation

Explanation:

Reproductive barriers can be pre - zygotic (preventing fertilization) or post - zygotic (acting after fertilization). Gametic isolation is a pre - zygotic barrier where gametes (sperm and egg) cannot fuse. Mechanical isolation is also pre - zygotic, related to physical incompatibility of reproductive organs. Here, the lion and tiger can mate (fertilization occurs) but the hybrid is sterile. Postzygotic barriers come into play after fertilization. Hybrid sterility (as in this case) is a postzygotic barrier.

Answer:

a postzygotic barrier