Postzygotic isolating mechanism

From Study Force Dictionary

1) A mechanism that prevents interbreeding by blocking the development of a viable and fertile individual after fertilization has taken place.

2) A type of reproductive isolating mechanism which comes into play after the gametes of two different species have fused to create a hybrid zygote. These mechanisms may prevent the proper development of the hybrid and/or make it infertile, thus the hybrid is unable to successfully reproduce.