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Male sperm cells in humans and other mammals are heterogametic and contain one of two types of sex chromosomes. They contain either an X chromosome or a Y chromosome. Female egg cells however, contain only the X sex chromosome and are therfore homogametic. The sperm cell determines the sex of an individual. If a sperm cell containing an X chromosome fertilizes an egg, the resulting zygote will be XX or female.
Gametes are an organism's reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells.