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Sex is the trait that determines whether a sexually reproducing organism produces male or female gametes. Male plants and animals produce small mobile gametes (spermatozoa, sperm, pollen), while females produce larger, non-motile ones (ova, often called egg cells). Organisms that produce both types of gametes are called hermaphrodites. During sexual reproduction, male and female gametes fuse to form zygotes, which develop into offspring that inherit traits from each parent.
Males and females of a species may have physical similarities (sexual monomorphism) or differences (sexual dimorphism) that reflect various reproductive pressures on the respective sexes. 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 individuals are isomorphic (look the same) and the gametes are isogamous (indistinguishable in size and shape), such as the green alga Ulva lactuca. Some kinds of functional differences between gametes, such as in fungi, may be referred to as mating types.
The sex of a living organism is determined by its genes. Most mammals have the XY sex-determination system, where male mammals usually carry an X and a Y chromosome (XY), whereas female mammals usually carry two X chromosomes (XX). Other chromosomal sex-determination systems in animals include the ZW system in birds, and the X0 system in insects. Various environmental systems include temperature-dependent sex determination in reptiles and crustaceans.
Sex: Either of the two main categories (male and female) into which humans and most other living things are divided on the basis of their reproductive functions. The fact of belonging to one of these categories. The group of all members of either sex.
A single body can function as both male and female. Sexual reproduction requires both male and female haploid gametes. In most species, these gametes are produced by individuals that are either male or female. Species that have male and female members are called dioecious (from the Greek for 'two houses'). In some species, a single individual may possess both female and male reproductive systems. Such species are called monoecious ("one house") or hermaphroditic.
The answer is that there is an agreement by convention: individuals producing the smaller of the two gamete types – sperm or pollen – are males, and those producing larger gametes – eggs or ovules – are females.
Anisogamy can be defined as a mode of sexual reproduction in which fusing gametes, formed by participating parents, are dissimilar in size.
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