Sexual reproduction in eukaryotes is a process whereby organisms form offspring that combine genetic traits from both parents.Chromosomes are passed on from one generation to the next in this process.In addition to animals, plants, and fungi, other eukaryotes (e.g.

the origin of chromosomal sex determination may have been fairly early in eukaryotes (see Evolution of anisogamy).

The ZW sex-determination system is shared by birds, some fish and some crustaceans.

XY sex determination is used by most mammals, and from a comparison between chicken and human, the Z chromosome appeared similar to the autosomal chromosome 9 in human, rather than X or Y, suggesting that the ZW and XY sex-determination systems do not share an origin, but that the sex chromosomes are derived from autosomal chromosomes of the common ancestor of birds and mammals.

A paper from 2004 compared the chicken Z chromosome with platypus X chromosomes and suggested that the two systems are related.

The gametes produced by an organism are determined by its sex: males produce male gametes (spermatozoa, or sperm, in animals; pollen in plants) while females produce female gametes (ova, or egg cells); individual organisms which produce both male and female gametes are termed hermaphroditic.

Frequently, physical differences are associated with the different sexes of an organism; these sexual dimorphisms can reflect the different reproductive pressures the sexes experience.

The resulting cells are called gametes, and contain only half the genetic material of the parent cells.

These gametes are the cells that are prepared for the sexual reproduction of the organism.

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).

In complex organisms, the sex organs are the parts that are involved in the production and exchange of gametes in sexual reproduction.

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.