ZW Sex-determination System: Sexual Differentiation, Sex-determination System, Haplodiploid Sex-determination System, X Chromosome - Tapa blanda

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The ZW sex-determination system is a system that determines the sex of offspring in birds, some fish, and some insects (including butterflies and moths), and some reptiles, including Komodo dragons. In the ZW system it is the ovum that determines the sex of the offspring, in contrast to the XY sex-determination system and the X0 sex-determination system, where it is the sperm which determines the sex. The letters Z and W are used to distinguish this system from the XY system. Males are the homogametic sex (ZZ), while females are heterogametic (ZW). The Z chromosome is larger and has more genes, like the X chromosome in the XY system. It is unknown whether the presence of the W chromosome induces female features or the duplication of the Z chromosome induces male ones; unlike mammals, no birds with a double W chromosome (ZWW) or a single Z (Z0) have been discovered. It is possible that either condition causes embryonic death, or that both chromosomes are responsible for gender selection.