Birth Definitions

Zygote Definition


A zygote is a fertilized egg cell that results from the union of two gametes. The zygote’s genetic makeup is determined by the DNA of the male and female gametes. The zygote’s DNA determines the baby’s sex, hair and eye color, and other physical characteristics.

The zygote stage lasts for about two weeks, during which time the zygote divides into a blastocyst. The blastocyst is a ball of cells that implant in the uterus and begin to grow.

Pregnancy is a time of great change for the mother-to-be. Her body must adapt to the growing baby, and her hormones must be carefully balanced to support the pregnancy. The zygote stage is a critical time in the development of the baby, and any complications during this time can result in birth defects or miscarriage.


The term zygote is often used interchangeably with fertilized egg, but there is a distinction between the two. A zygote is a fertilized egg that has not yet been implanted in the uterus. An egg that has been implanted is called a blastocyst.

There are a few terms that are closely associated with zygote:

Gamete: A gamete is a mature sex cell that contains half of the genetic information needed to create a new life. Male gametes are called sperm, and female gametes are called eggs.

Fertilization: Fertilization is the process of the sperm and egg joining to form a zygote.

Embryo: An embryo is a developing human from the time of fertilization until eight weeks of gestation.

Fetus: A fetus is a developing human from eight weeks of gestation until birth.

This image shows how often the term ‘Zygote’ is used in relation to other, similar birth terms:

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