embryogenesis

Embryogenesis is the process by which a zygote develops into a multicellular embryo, marking the early stages of development in animals and the formation of a seed embryo in plants. It includes fertilization, rapid cell division, patterning, and cell differentiation that establish the body plan.

In animals, embryogenesis begins with fertilization, followed by cleavage divisions that produce a multicellular embryo. The resulting morula hollows out to form a blastula, which contains a cavity called the blastocoel. Gastrulation rearranges cells to form three germ layers—ectoderm, mesoderm, and endoderm—giving rise to all tissues and organs. Subsequent steps such as neurulation and organogenesis further shape the embryo, with development controlled by intricate signaling networks and gene regulation. Timing and specific events vary among species, but the general sequence of cleavage, pattern formation, and tissue differentiation is conserved.

In plants, zygotic embryogenesis occurs within the ovule after fertilization and leads to a seed embryo. The embryo progresses through stages such as globular, heart, and torpedo forms before maturing. Plants also exhibit somatic embryogenesis, where somatic (non-reproductive) cells reprogram to form embryos in culture, often induced by plant hormones like auxin. Somatic embryogenesis is exploited for clonal propagation and genetic engineering.

Embryogenesis is central to developmental biology and evolution. It provides a framework for understanding how early cellular decisions translate into complex body plans, and disruptions in embryogenesis can result in congenital defects in animals or seed abortion in plants.