Gametes and Fertilization

In animals, sexual reproduction encompasses the fusion of two distinct gametes (sex cells) to form a zygote. Gametes are produced by a type of cell division called meiosis. When gametes unite in fertilization, a new individual is formed.
Gametes are haploid, containing only one set of chromosomes. For example, human gametes contain 23 chromosomes. After fertilization, a zygote is produced from the union of an egg and sperm. The zygote is diploid, containing two sets of 23 chromosomes for a total of 46 chromosomes.
There are two mechanisms by which fertilization can take place. The first is external (the eggs are fertilized outside of the body) and the second is internal (the eggs are fertilized within the female reproductive tract). In either case, each egg is fertilized by a single sperm to ensure that the correct chromosome numbers are preserved.

Sino Biological lists the classification tree of Gametes and Fertilization, click to see all the related molecules/targets and research reagents of them.