Fertilization occurs when a sperm and an oocyte egg combine and their nuclei fuse. Because each of these reproductive cells is a haploid cell containing half of the genetic material needed to form a human being, their combination forms a diploid cell. This new single cell, called a zygote , contains all of the genetic material needed to form a human—half from the mother and half from the father. Fertilization is a numbers game. During ejaculation, hundreds of millions of sperm spermatozoa are released into the vagina. Almost immediately, millions of these sperm are overcome by the acidity of the vagina approximately pH 3.
In the reproductive process, a male sperm and a female egg provide the information required to produce another human being. Conception occurs when these cells join as the egg is fertilized. Pregnancy begins once the fertilized egg implants in the uterus. The embryo grows and becomes surrounded by structures that provide support and nourishment. Eyes, limbs, and organs appear as the embryo develops into a fetus.