Embryology is the branch of developmental biology that studies the prenatal development of gametes (sex cells), fertilization, and the subsequent development of embryos and fetuses. It traces the intricate journey from a single-celled zygote through the complex processes of cell division, differentiation, and morphogenesis, which lead to the formation of tissues, organs, and the overall body plan of an organism. This field provides critical insights into congenital disorders, the mechanisms of growth, and the evolutionary relationships between different species by examining the earliest stages of life before birth, hatching, or metamorphosis.