A zygote is a fertilized egg caused by the combination
of a male sex cell (sperm) with a female sex cell
(ovum). More specifically, the zygote is formed when
sperm penetrates the ovum and when the nucleus of
the sperm combines with the nucleus of the ovum. The
nucleus is a structure in the center of a cell that
controls many of its activities. The nucleus of the sperm
and ovum each contain 23 chromosomes. Thus, when
the two cells are combined into a zygote, it will have 46
chromosomes. The zygote is the first stage of an
organism’s development.
A zygote.
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Chromosomes are structures in a person's cells that contain proteins and a substance
known as DNA (an abbreviation for deoxyribonucleic acid). DNA is a chain of many
connected genes. Genes are units of material contained in a person's cells that contain
coded instructions as for how certain bodily characteristics (such as eye color) will
develop. The zygote is a single cell that has yet to be divided. The genes instruct the
zygote to develop into an embryo. An embryo is a fertilized egg from the time of
conception until the 8th week of pregnancy. Zygote is also known as zygocyte.

Zygote comes from the Greek word “zygotes” meaning “yoked.”
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