Postzygotik

Postzygotik refers to mechanisms that prevent the successful production of viable or fertile offspring after a zygote has formed. These postzygotic barriers are one of the key factors contributing to reproductive isolation between species. Unlike prezygotic barriers, which act before fertilization, postzygotic barriers come into play after the gametes have fused to form a zygote.

There are several types of postzygotic barriers. Hybrid inviability occurs when the genes of the two parent species are incompatible, leading to developmental errors that prevent the zygote from maturing or surviving. Hybrid sterility is another common barrier, where hybrid offspring survive but are unable to reproduce due to chromosomal abnormalities or other genetic incompatibilities that prevent the formation of functional gametes. For example, a mule, the offspring of a horse and a donkey, is viable but sterile. Finally, hybrid breakdown describes situations where the first-generation hybrid offspring are fertile, but subsequent generations exhibit reduced viability or fertility, further reinforcing reproductive isolation. These postzygotic barriers are crucial in the evolutionary process of speciation, ensuring that distinct lineages remain reproductively separate.