XO sex-determination system
Biological system that determines the sex of offspring
XO sex-determination system
The XO sex-determination system (sometimes referred to as X0 sex-determination system) is a system that some species of insects, arachnids, and mammals (not including humans) use to determine the sex of offspring. In this system, there is only one sex chromosome, referred to as X. Males only have one X chromosome (XO), while females have two (XX). The letter O (sometimes a zero) signifies the lack of a Y chromosome. Maternal gametes always contain an X chromosome, so the sex of the animals' offspring depends on whether a sex chromosome is present in the male gamete. Its sperm normally contains either one X chromosome or no sex chromosomes at all. This system determines the sex of offspring among: Most arachnids with the exception of mites where a small majority are haplodiploid Almost all apterygote and Paleopteran insects (e.g., dragonflies, silverfish) Most exopterygote insects (e.g., grasshoppers, crickets, cockroaches) Some nematodes, crustaceans, gastropod molluscs, and bony fish...
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