Home > Encyclopedia of Science > Embryo and Embryonic Development

• Embryology
• Words to Know
• Embryonic development
• Continued development
• Embryo diagnosis
• Embryonic Transfer

The term embryo applies to the earliest form of life, produced when an egg (female reproductive cell) is fertilized by a sperm (male reproductive cell; semen). The fertilized egg is called a zygote. Shortly after fertilization, the zygote begins to grow and develop. It divides to form two cells, then four, then eight, and so on. As the zygote and its daughter cells divide, they start to become specialized, meaning they begin to take on characteristic structures and functions that will be needed in the adult plant or animal.

An embryo is a living organism, like a full-grown rose bush,...