Sex determination
- Genetic sex determination
- different alleles, genes, even chromosomes
- XX/XY-sex determination -
- "In the XY sex-determination system, females have two of the same kind of sex chromosome (XX), while males have two distinct sex chromosomes (XY)."[1]
- e.g., Homo sapiens
- XX/XO-sex determination
- "In this variant of the XY system, females have two copies of the sex chromosome (XX) but males have only one (X0). The 0 denotes the absence of a second sex chromosome."[1]
- ZW-sex determation
- "The ZW sex-determination system is reversed compared to the XY system: females have two different kinds of chromosomes (ZW), and males have two of the same kind of chromosomes (ZZ)."[1]
- e.g., birds, some insects
- haplodiploidy
- "Haplodiploidy is found in insects belonging to Hymenoptera, such as ants and bees. Unfertilized eggs develop into haploid individuals, which are the males. Diploid individuals are generally female but may be sterile males. Thus, if a queen bee mates with one drone, her daughters share ¾ of their genes with each other, not ½ as in the XY and ZW systems."[1]
- Temperature-dependent sex determination
- e.g., crocodiles
- Social-dependent sex determination
- "In tropical clown fish, the dominant individual in a group becomes female while the other ones are male, and blue wrasse fish are the reverse."[1]
- "In the marine worm Bonellia viridis, larvae become males if they make physical contact with the female, and females if they end up on the bare sea floor."[1]
- Nutrition-dependent sex determination
- Infectious sex determination
- some arthropods; Wolbachia genus bacteria: "some species consist entirely of ZZ individuals, with sex determined by the presence of Wolbachia."[1]
- Sex change life cycle
- e.g., snails; begin male then become female
- No sex-determination system
- hermaphroditic - common earthworm, some snails
- parthenogenetic - all female; e.g., some fish, reptiles, insects
Further reading
- "Sex-determination system", Wikipedia
- Biological Exuberance (same-sex sexuality / sociality in animals)
References
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