Egg (biology)

Egg (biology)

An egg is the organic vessel containing the zygote in which an animal embryo develops until it can survive on its own, at which point the animal hatches. An egg results from fertilization of an ovum. Most vertebrates, including mammals, birds, reptiles, and fish, lay eggs, while some, such as most mammals, do not.

Structure and composition

The egg is composed of the egg yolk, the egg white, and the shell. The yolk contains the zygote, while the white provides nutrients and the shell protects the developing embryo.

Fertilization and development

Fertilization occurs when a sperm cell penetrates the egg, combining the genetic material of both parents. The fertilized egg, or zygote, then begins to divide and grow into an embryo.

Types of eggs

Different animals produce different types of eggs. Mammals produce amniotic eggs, while birds and reptiles produce oviparous eggs. Fish and amphibians produce ovoviviparous eggs.

See also

• Ovum
• Zygote
• Embryo
• Fertilization
• Amniotic egg
• Oviparous egg
• Ovoviviparous egg

Egg (biology) Resources
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