Human Growth and Development


How do the terms zygote, embryo, and fetus differ?

All three terms refer to the individual developing within the uterus of a woman following conception. Fertilization between sperm and ovum produces a zygote, a single cell consisting of 46 chromosomes. It is called a zygote during the first week of development. At the end of the first week of development, the zygote becomes an embryo. It is called an embryo from the second week of development through the eighth week of development. Beginning at the ninth week of development, it is called a fetus.


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