Fertilized

Fertilized describes a cell, egg, or organism in which fertilization has occurred. In biology, fertilization is the fusion of male and female gametes to form a zygote, a single cell that carries genetic material from both parents. Fertilization initiates embryonic development and typically marks the beginning of pregnancy in animals or seed formation in plants.

In animals, fertilization can be internal or external. Internal fertilization occurs when sperm is deposited inside the female body and meets the egg within the reproductive tract; external fertilization occurs in many aquatic species where eggs and sperm are released into the environment. A fertilized egg (zygote) undergoes cleavage divisions to form multicellular early embryos and, in many species, implants into the uterus.

In flowering plants, fertilization involves pollen from the male anther reaching the ovule in a ovary via a pollen tube. Angiosperms often exhibit double fertilization: one sperm fertilizes the egg to form a diploid zygote, and another sperm fuses with two polar nuclei to form triploid endosperm, which nourishes the developing embryo.

In human-assisted reproduction, fertilization can be achieved or enhanced in vitro (in a laboratory) as part of in vitro fertilization (IVF). Here, eggs and sperm are combined outside the body and resulting embryos are transferred to the uterus for implantation.

Fertilized eggs, embryos, seeds, and organisms are distinguished from their unfertilized counterparts by their developmental potential and the physiological processes that follow fertilization.