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==Sex determination==
{{main|Sex-determination system}}
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, [[hermaphrodite|hermaphroditic]] animals have both male and female reproductive organs. Female humans obtain a certain body part called the [[vagina]].
===Genetic determination===
Most [[mammal]]s, including [[human]]s, 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 [[bird]]s and some [[insect]]s and other organisms. Members of [[Hymenoptera]], such as [[ant]]s and [[bee]]s, are determined by [[haplodiploidy]], where most males are [[haploid]] and females and some sterile males are [[diploid]].
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