Sexual reproduction involves the combining and mixing of genetic traits: specialized cells known as gametes combine to form offspring that inherit traits from each parent.

Gametes can be identical in form and function (known as isogamy), but in many cases an asymmetry has evolved such that two sex-specific types of gametes (heterogametes) exist (known as anisogamy).

Each cell in the offspring has half the chromosomes of the mother and half of the father.

Genetic traits are contained within the deoxyribonucleic acid (DNA) of chromosomes—by combining one of each type of chromosomes from each parent, an organism is formed containing a doubled set of chromosomes.

In addition to animals, plants, and fungi, other eukaryotes (e.g.

the malaria parasite) also engage in sexual reproduction.

This mode of reproduction is called asexual, and it is still used by many species, particularly unicellular, but it is also very common in multicellular organisms.

In sexual reproduction, the genetic material of the offspring comes from two different individuals.

Many species, particularly animals, have sexual specialization, and their populations are divided into male and female individuals.

Conversely, there are also species in which there is no sexual specialization, and the same individuals both contain masculine and feminine reproductive organs, and they are called hermaphrodites. The reason for the evolution of sex, and the reason(s) it has survived to the present, are still matters of debate.

Multiplicity of gamete types within a species would still be considered a form of sexual reproduction.

However, no third gamete is known in multicellular animals.

Sex comprises the arrangements that enable sexual reproduction, and has evolved alongside the reproduction system, starting with similar gametes (isogamy) and progressing to systems that have different gamete types, such as those involving a large female gamete (ovum) and a small male gamete (sperm).