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Avian sex

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    Sure, birds can fly, but how do they have sex? Can they do it in the air? And where do they keep their reproductive organs? For humans to understand bird sex, they must first throw out all thoughts of mammalian sex organs.
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    Avian Sex Chromosomes and Sex-Linked Genes

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    Avian Sex Chromosomes and Sex-Linked Genes | SpringerLink

    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 , and some reptiles, including Komodo dragons. It is also used in some plants where it has probably evolved independently on several occasions. In this system, females have a pair of dissimilar ZW chromosomes , and males have two similar ZZ chromosomes. In contrast to the XY sex-determination system and the X0 sex-determination system , where the sperm determines the sex, in the ZW system, the ovum determines the sex of the offspring. Males are the homogametic sex ZZ , while females are the heterogametic sex ZW. The Z chromosome is larger and has more genes, like the X chromosome in the XY system.
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    Avian sex determination: what, when and where?

    Chromosomes Today pp Cite as. In contrast to mammals, female birds are the heterogametic sex, carrying one copy each of the Z and W sex chromosomes, whereas the homogametic males have two identical Z chromosomes. Given the very distinct nature of mammalian and avian sex chromosomes, the sex determination pathway in birds is unlikely to resemble that in mammals, where the presence of the SRY gene product exclusively in males regulates expression of a cascade of downstream genes that triggers male sexual development. In addition, the failure to detect an avian SRY homolog s argues against its role in avian sex determination. However, a recent study suggests that at least some genes associated with gonadal development are conserved among mammals and birds Smith et al.
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    Comparisons of the sex chromosome systems in birds and mammals are widening our view and deepening our understanding of vertebrate sex chromosome organization, function, and evolution. Birds have a very conserved ZW system of sex determination in which males have two copies of a large, gene-rich Z chromosome, and females have a single Z and a female-specific W chromosome. The avian ZW system is quite the reverse of the well-studied mammalian XY chromosome system, and evolved independently from different autosomal blocs.