Postzygotical

Postzygotical refers to events or processes that occur after the formation of a zygote. A zygote is the initial cell formed when two gametes, such as an egg and a sperm, fuse during fertilization. Therefore, postzygotical events encompass everything that happens from this point onwards in the development of an organism.

This broad term can include a wide range of biological phenomena. In sexual reproduction, postzygotical developments begin with the zygote undergoing rapid cell division, a process known as cleavage, to form an embryo. This embryonic development involves cell differentiation, morphogenesis (the shaping of tissues and organs), and growth. Beyond the embryonic stage, postzygotical development continues throughout fetal development, childhood, adolescence, and into adulthood.

The term can also be used in the context of reproductive isolation, specifically referring to postzygotic isolation mechanisms. These are biological barriers that act after fertilization has occurred, preventing a hybrid zygote from developing into a viable, fertile adult. Examples include hybrid inviability, where the hybrid embryo or fetus does not survive, or hybrid sterility, where the hybrid offspring is born but is unable to reproduce. In essence, postzygotical describes any stage or barrier that manifests after the initial union of gametes.