The genotype of a normal human male is XY. Humans have 23 pairs of chromosomes in all body cells, and the 23rd pair consists of the sex chromosomes, X and Y. The mothers set combines with the fathers, resulting in 23 pairs of chromosomes that contain the genetic information that determines everything from sex to eye color. When a sperm carrying the Y chromosome fertilizes an egg, the resulting embryo has a genotype of XY and will be a male. With rare exceptions, all other embryos will be XX or female.