Final answer:
Reproductive isolation includes prezygotic and postzygotic barriers. Intrinsic postmating isolating mechanisms are genetic incompatibilities within organisms, while extrinsic mechanisms are due to external factors. Understanding these mechanisms, especially in plants, assists in breeding and species interactions.
Step-by-step explanation:
In biology, reproductive isolation mechanisms are categorized into two groups: prezygotic barriers and postzygotic barriers. Prezygotic barriers occur before fertilization, impeding different species from mating or ensuring fertilization does not occur. Postzygotic barriers, on the other hand, take place after the formation of a zygote. Intrinsic postmating isolating mechanisms are internal to the organisms and include genetic incompatibilities that may disrupt the development of the offspring or render them sterile, such as the mechanism causing mules to be sterile. Extrinsic postmating isolating mechanisms are external factors that impede the survival or reproduction of hybrids, often due to environmental factors or ecological interactions.
In the context of plants, dissecting reproductive barriers like self-incompatibility (SI) helps understand pollen-pistil interaction, crucial for breeding and reproduction. In SI, proteins encoded by highly polymorphic S loci in pistils and pollen govern recognition and rejection during reproduction, an intrinsic barrier. Additionally, polyploidy, the presence of extra chromosomes in gametes, can serve as an intrinsic postzygotic barrier, often leading to reproductive isolation and even speciation.