The cell that is produced when a sperm fertilizes an ovum. A zygote, measuring about 0.1 mm in diameter in humans, contains all the genetic material for a new individual. The zygote is surrounded by a protein-rich layer known as the zona pellucida. The zygote travels down 1 of the woman’s fallopian tubes, dividing as it does so. After about a week, the mass of cells (now called a blastocyst) implants into the lining of the uterus, and the next stage of embryological growth begins. (See also embryo; fertilization.)


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