page_title: Sex-determination system
section_title: UV sex chromosomes
hierarchical_section_title: Sex-determination system / Chromosomal systems / UV sex chromosomes
caption_attribution_description: Haplodiploid-sex-determination-system　半倍数性
context_page_description: A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two sexes. Occasionally, there are hermaphrodites in place of one or both sexes. There are also some species that are only one sex due to parthenogenesis, the act of a female reproducing without fertilization.
  In many species, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual morphology. In animals this is often accompanied by chromosomal differences, generally through combinations of XY, ZW, XO, ZO chromosomes, or haplodiploidy. The sexual differentiation is generally triggered by a main gene, with a multitude of other genes following in a domino effect.
  In other cases, sex of a fetus is determined by environmental variables. The details of some sex-determination systems are not yet fully understood.
context_section_description: In some Bryophyte and some algae species, the gametophyte stage of the life cycle, rather than being hermaphrodite, occurs as separate male or female individuals that produce male and female gametes respectively. When meiosis occurs in the sporophyte generation of the life cycle, the sex chromosomes known as U and V assort in spores that carry either the U chromosome and give rise to female gametophytes, or the V chromosome and give rise to male gametophytes.
caption: Haplodiploid sex chromosomes
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