The ZW sex-determination system is a chromosomal system that determines the sex of offspring in birdssome fish and crustaceans such as the giant river prawnsome insects including butterflies and mothsand some reptiles, including Komodo dragons. The letters Z and W are used to distinguish this system from the XY sex-determination system. In this system, female has a pair of dissimilar ZW chromosomes and male has two similar ZZ chromosomes.
Ellegren ebc. Degeneration of the nonrecombining chromosome is a common feature of sex chromosome evolution, readily evident by the presence of a pair of largely heteromorphic chromosomes, like in eutherian mammals and birds. However, in ratites order Palaeognathae, including, e.
Identifying the processes involved in the evolution of suppressed recombination between sex chromosomes and understanding their consequences for the evolutionary dynamics of sex-linked loci have been major topics of research during the last century. In this thesis, I used the avian ZW system, where females are the heterogametic sex, to investigate the underlying processes in sex chromosome evolution in birds. I identified the gametologous genes between the largely recombining Z and W chromosomes of ostrich and dated the timing of the cessation of recombination to prior to the split of modern birds.
Distinct phenotypic sexual dimorphism servers as one of the key factors that can enable one to categorize the individual to a particular sex. However in case of ratite bird emu Dromaius novaehollandiae this phenotypic distinctness between males and females is less evident and careful observation of adult birds would help to identify the sexes. Other methods of sex identification such as the sexing by feather pattern observation, vent sexing, surgical sexing and karyotyping do not appear to yield confirmatory results.
Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer.
Reptiles have a wide diversity of sex-determining mechanisms and types of sex chromosomes. Identification of sex chromosomes in many turtle species and their comparative genomic analysis are of great significance to understand the evolutionary processes of sex determination and sex chromosome differentiation in Testudines. The Mexican giant musk turtle Staurotypus triporcatusKinosternidae, Testudines and the giant musk turtle Staurotypus salvinii have heteromorphic XY sex chromosomes with a low degree of morphological differentiation; however, their origin and linkage group are still unknown.
Kiwi represent the most basal extant avian lineage paleognaths and exhibit biological attributes that are unusual or extreme among living birds, such as large egg size, strong olfaction, nocturnality, flightlessness and long lifespan. Despite intense interest in their evolution and their threatened status, genomic resources for kiwi were virtually non-existent until the recent publication of a single genome. Here we present the most comprehensive kiwi transcriptomes to date, obtained via Illumina sequencing of whole blood and de novo assembly of mRNA sequences of eight individuals from each of the two rarest kiwi species, little spotted kiwi LSK; Apteryx owenii and rowi A. Sequences obtained were orthologous with a wide diversity of functional genes despite the sequencing of a single tissue type.