The fertilized egg is called as a

A) Uterus

B) Ovary

C) Gametes

D) Zygote

To answer this, we first need to understand the process of fertilization. Fertilization is the union of a male sperm cell and a female egg cell, resulting in the formation of a zygote that later develops into a fetus inside the uterus.

During sexual intercourse, semen released by the male contains thousands of sperm cells. These sperm travel toward the uterus and move to the opening of the fallopian tube. Out of the thousands, only a few manage to reach the fallopian tube. 

Meanwhile, a secondary oocyte, released from the matured Graafian follicle of the ovary, enters the fallopian tube. The oocyte may be surrounded by many sperms, but only one sperm successfully penetrates it.

The sperm enters the secondary oocyte during the meiosis II phase, completing the division to form a mature egg. Within 48 to 72 hours, the sperm and egg fuse, producing a zygote.

Fertilization can be of two types:

• External fertilization: The fusion of sperm and egg occurs outside the body, in an open environment. This is common in egg-laying animals such as frogs and many fishes.
• Internal fertilization: The fusion happens inside the female body, following copulation. Animals like whales and sharks undergo this process.

Thus, the correct option is D. Zygote.