sex

Sex is a trait that determines an individual's reproductive function, male or female, in animals and plants that propagate their species through sexual reproduction. Sexual reproduction involves the recombination of genes by meiosis followed by the formation of specialized haploid cells known as gametes. Pairs of gametes fuse to form diploid zygotes that develop into offspring that inherit a selection of the traits of each parent. The type of gametes produced by an organism defines its sex. Commonly in plants and animals, male organisms produce smaller gametes (spermatozoa, sperm) while female organisms produce larger gametes (ova, often called egg cells).Male and female individuals of a species may be similar, or have physical differences (sexual dimorphism). The differences reflect the different reproductive pressures the sexes experience. For instance, mate choice and sexual selection can accelerate the evolution of physical differences between the sexes.
The terms "male" and "female" typically do not apply in sexually undifferentiated species in which the parents are isomorphic and the gametes are isogamous (indistinguishable in size and morphology), such as the green alga Ulva lactuca. If there are instead functional differences between gametes, such as with fungi, they may be referred to as mating types. Organisms that produce both types of gametes are called hermaphrodites.Sex is determined by a variety of processes. Most mammals have the XY sex-determination system, where male mammals carry an X and a Y chromosome (XY), whereas female mammals carry two X chromosomes (XX). Other sex-determination systems in animals include the ZW system in birds, the X0 system in insects, and various environmental systems, such as those of reptiles and crustaceans.

View More On Wikipedia.org