Male

In heterogamous species, male is the sex of an organism, or of a part of an organism, which typically produces smaller, mobile gametes (spermatozoa) that are able to fertilise female gametes (ova). A male individual cannot reproduce sexually without access to the gametes of a female. more...

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There is no single genetic sex-determination system which controls sex differences in different species. The existence of two sexes seems to have evolved multiple times independently in different evolutionary lineages. Other than the defining difference in the type of gamete produced, differences between males and females in one lineage cannot always be predicted by differences in another.

The concept of male/female dimorphism between individuals or reproductive organs is not limited to animals; male gametes are produced by chytrids, diatoms, and land plants, among others. In land plants, female and male designate not only the female and male gamete-producing organisms and structures, but also the structures of the sporophytes that give rise to male and male plants.

Secondary sex characteristics

In those species with same sexes, males may differ from females in ways other than production of spermatozoa. Males are generally smaller than females in seed plants (the pollen grain is the male plant) and many fishes and birds, but larger in many mammals, including humans. In birds, the male often exhibits a colourful plumage which is used to attract females.

Sex determination

The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism's life. Although most species with male and female sexes have individuals that are either male or female, hermaphroditic animals have both male and female reproductive organs.

Genetic determination

Most mammals, including humans, are genetically determined as such by the XY sex-determination system where males have an XY (as opposed to XX) sex chromosome. During reproduction, a male can give either an X sperm or a Y sperm, while a female can only give an X egg. A Y sperm and an X egg produce a boy, while an X sperm and an X egg produce a girl. The ZW sex-determination system, where males have a ZZ (as opposed to ZW) sex chromosome may be found in birds and some insects and other organisms. Members of Hymenoptera, such as ants and bees, are determined by haplodiploidy, where most males are haploid and females and some sterile males are diploid.

Environmental determination

In some species of reptiles, including alligators, sex is determined by the temperature at which the egg is incubated. Other species, such as some snails, practice sex change: adults start out male, then become female. In tropical clown fish, the dominant individual in a group becomes female while the other ones are male.

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