What occurs when postzygotic barriers are present?

The presence of postzygotic barriers affects the viability or reproductive capabilities of offspring that result from fertilization. In this context, postzygotic barriers come into play after hybridization has occurred, meaning fertilization has taken place, but the resulting offspring are either non-viable or sterile.

For example, when two different species mate and produce offspring, but those offspring cannot survive to adulthood or are infertile, this scenario illustrates postzygotic isolation. A classic case is the mating of a horse and a donkey, producing a mule, which is generally sterile. Hence, the key aspect of postzygotic barriers is that they impede the successful propagation of a new generation, resulting in the inability of those hybrids to contribute to further reproduction, which is exactly what option B describes. This concept is pivotal in understanding speciation and the mechanisms through which species remain biologically distinct despite potential interbreeding.