ZW sex-determination system in the context of "Crustaceans"

Sex is the biological trait that determines whether an anisogamous sexually reproducing organism produces male or female gametes. During sexual reproduction, a male and a female gamete fuse to form a zygote, which develops into an offspring that inherits traits from each parent. By convention, organisms that produce smaller gametes (spermatozoa, sperm) are called male, while organisms that produce larger gametes (ova, often called egg cells) are called female. An organism that produces both types of gamete is a hermaphrodite.

In non-hermaphroditic species, the sex of an individual is determined through one of several biological sex-determination systems. Most mammalian species have the XY sex-determination system, where the male usually carries an X and a Y chromosome (XY), and the female usually carries two X chromosomes (XX). Other chromosomal sex-determination systems in animals include the ZW system in birds, and the XO system in some insects. Various environmental systems include temperature-dependent sex determination in reptiles and crustaceans.

The pseudoautosomal regions or PARs are homologous sequences of nucleotides found within the sex chromosomes of species with an XY or ZW mechanism of sex determination.

The pseudoautosomal regions get their name because any genes within them (so far at least 29 have been found for humans) are inherited just like any autosomal genes. In humans, these regions are referred to as PAR1 and PAR2. PAR1 comprises 2.6 Mbp of the short-arm tips of both X and Y chromosomes in humans and great apes (X and Y are 154 Mbp and 62 Mbp in total). PAR2 is at the tips of the long arms, spanning 320 kbp. The monotremes, including the platypus and echidna, have a multiple sex chromosome system, and consequently have 8 pseudoautosomal regions.