Embryology is the branch of biology that studies the prenatal development of gametes, fertilization, and development of embryos and fetuses. Additionally, embryology encompasses the study of congenital disorders that occur before birth, known as teratology. Embryology Definition. Embryology is the branch of biology concerned with the development of new organisms. Embryologists track reproductive cells (gametes) as they progress through fertilization, become a single-celled zygote, then an embryo, all the way to a fully functioning organism.