Sources – Science

“[O]ne of two cells, male and female, whose union is necessary in sexual reproduction, to initiate the development of a new individual.” 142 142 Dorland’s Illustrated Medical Dictionary, (24th edition, 1965), 595.

“[E]mbryo (em’bre-o) a new organism in the earliest stage of development; the human young from the time of fertilization of the ovum until the beginning of the third month.” ” 140 140 Encyclopedia and Dictionary of Medicine, Nursing and Allied Health (Philadelphia: WB Sanders Co., 1978) 2nd edition, 335.

“[T]he beginning of the development of a new individual, is the fusion of two germ cells (gametes) of different nature; one, the spermatozoon from the male parent; the other, the ovum from the female parent. The result of this fusion is the formation of the first cell of the new individual, the zygote.” 139 139…

“These pronuclei [of the sperm and oocyte] fuse with each other to produce the single, diploid 2N nucleus of the fertilized zygote. This moment of zygote formation may be taken as the beginning or zero time point of embryonic development.” 136 136 Larsen, W.J., Essentials of Human Embryology, (New York: Churchill Livingstone, 1998), 14.

“The development of a human being begins with fertilization, a process by which two highly specialized cells, the spermatozoon from the male and the oocyte from the female, unite to give rise to a new organism, the zygote.” 134 134 Langman, J., Medical Embryology. 3rd edition, Baltimore: Williams and Wilkins, 1975, 3.