Conception

Egg and Sperm

1: Nucleus 2: Plasma membrane 3: Jelly layer

The Female Sex Cell: Egg
The female sex cell is called egg (ovum, plural: ova). Eggs are produced in the female gonads or sex glands (ovaries), and they are the largest cells in the human body. They are visible to the naked eye, being about the size of the dot at the end of this sentence. The contrast in volume between egg and sperm is immense. It would take only the combined total length of three sperm cells to span the diameter of one egg, but the egg's volume is 85,000 times greater than that of the sperm. (For details about the production of eggs, click here)
The egg is round in shape and it contains twenty three special bodies (chromosomes) which carry the woman's inheritable characteristics. Among them is an X-chromosome. (In contrast, sperm may carry either an X-chromosome or a Y-chromosome.) If an egg unites with a sperm that also carries an X chromosome, the child resulting from that union will be a girl. However, if the same egg should unite with a sperm carrying a Y chromosome, the child would be a boy. In other words, the sex of a child is determined not by the content of the egg, but by that of the sperm. The egg does not leave the woman's body in order to unite with the sperm. Instead, the sperm has to be brought to the egg if a fertilization is to be possible.
Once the female sex glands have matured during puberty, they normally release not more than one egg per month. Even so, in the course of a woman's life their total number may very well reach more than 400. Obviously, most of them will never be fertilized and thus never contribute to actual conceptions. Instead, they simply die and dissolve.