Image caption : Sperm and Oocyte During Fertilization: Computer Generated Image from Micro-MRI, actual size of zygote = 0.1 mm - This image captures the moment of fertilization, when a sperm breaks through the oocyte's outer shell and breaches the inner membrane. Once fertilized, the egg becomes a zygote, which then begins its 3-day descent to the uterus via the fallopian tubes.

Fertilization (also known as conception, fecundation, syngamy and impregnation) is the fusion of gametes to initiate the development of a new individual organism. In animals, the process involves the fusion of an ovum with a sperm, which first creates a zygote and then leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside (external fertilization). The cycle of fertilization and development of new individuals is called sexual reproduction.

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