Recall that sexual reproduction is the creation of new individuals from the merger of genetic material from two parents, through the fertilization of the female's egg with the male's sperm. . . .In humans, who have 46 chromosomes (23 pairs) in each cell nucleus , the egg contains 23 chromosomes, as does the sperm. When the sperm fertilizes the egg, the sperm contents can penetrate the egg's cell membrane, so that the chromosomes form the egg and those from the sperm constitute the 23 pairs of the fertilized egg. Once fertilized, the egg is known as a zygote.