The Developing Human: Clinically Oriented Embryology, 6th ed. Keith L. Moore, Ph.D. & T.V.N. Persaud, Md., (Philadelphia: W.B. Saunders Company, 1998), 2-18:
“[The Zygote] results from the union of an oocyte and a sperm. A zygote is the beginning of a new human being. Human development begins at fertilization, the process during which a male gamete or sperm … unites with a female gamete or oocyte … to form a single cell called a zygote. This highly specialized, totipotent cell marks the beginning of each of us as a unique individual.”
From Human Embryology & Teratology, Ronan R. O’Rahilly, Fabiola Muller, (New York: Wiley-Liss, 1996), 5-55.
“Fertilization is an important landmark because, under ordinary circumstances, a new, genetically distinct human organism is thereby formed… Fertilization is the procession of events that begins when a spermatozoon makes contact with a secondary oocyte or its investments… The zygote … is a unicellular embryo..”
Essentials of Human Embryology, William J. Larsen, (New York: Churchill Livingstone, 1998), 1-17.
“In this text, we begin our description of the developing human with the formation and differentiation of the male and female sex cells or gametes, which will unite at fertilization to initiate the embryonic development of a new individual. … Fertilization takes place in the oviduct … resulting in the formation of a zygote containing a single diploid nucleus. Embryonic development is considered to begin at this point… This moment of zygote formation may be taken as the beginning or zero time point of embryonic development.”