ZW sex-determination system

The ZW sex-determination system is a chromosomal system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects (including butterflies and moths), the schistosome family of flatworms, and some reptiles, e.g. majority of snakes, lacertid lizards and monitors, including Komodo dragons.

They form a multiple chain due to homologous regions in male meiosis and finally segregates into XXXXX-sperm and YYYYY-sperm.

[6] In 2007, a time where there had not been extensive research on other organisms with the ZW sex-determination system, researchers announced that chickens' and zebra finches' sex chromosomes do not exhibit any type of chromosome-wide dosage compensation, and instead seem to dosage compensate on a gene-by-gene basis.

[14] In addition, the involvement of sex-biased miRNAs was proposed to compensate for the presence of two Z-chromosomes in male birds.

[20] Python bivittatus and Boa imperator, similarly only produce female offspring; their genomes share male-specific single nucleotide polymorphisms identifiable by restriction enzyme digestion.

[21] The female-only pattern is in contrast to the ZW Colubroidean parthenogens, which always produce male (ZZ) offspring.

They are the only sexually heteromorphic family among the trematode class, and depend on remaining biochemically paired in copula to complete their life cycle.

[24] The heterogametic sex chromosomes in females of nine species of schistosomes were first described by geneticist Margaret Menzel and parasitologist Robert B.

Trionychidae turtles possess a ZZ-ZW sex determinate system, which originated sometime between the beginning of the Jurassic and the Early Cretaceous.

[27] Among the approximately 5% of plant species that have separate male and female individuals (dioecious), several are known to have a ZW system of sex determination.