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The black-chinned hummingbird (Archilochus alexandri) is the bird species known to have the smallest genome among birds, which is only 0.91 Gb long.The genomic evolution of birds has come under scrutiny since the advent of rapid DNA sequencing, as birds have the smallest genomes of the amniotes despite acquiring highly derived phenotypic traits.
The evolution of birds began in the Jurassic Period, with the earliest birds derived from a clade of theropod dinosaurs named Paraves. [1] Birds are categorized as a biological class, Aves. For more than a century, the small theropod dinosaur Archaeopteryx lithographica from the Late Jurassic period was considered to have been the earliest bird.
Genomic streamlining has been used to explain certain eukaryotic genome sizes as well, particularly bird genomes. Larger genomes require a larger nucleus, which typically translates to a larger cell size. [23] For this reason, many bird genomes have also been under selective pressure to decrease in size.
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.
Birds (except Falconidae) usually have karyotypes of approximately 80 chromosomes (2n = 80), with only a few being distinguishable macrochromosomes and an average of 60 being microchromosomes. [7] They are more abundant in birds than any other group of animals. Chickens (Gallus gallus) are an important model organism for studying ...
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Homologous sequences are paralogous if they were created by a duplication event within the genome. For gene duplication events, if a gene in an organism is duplicated, the two copies are paralogous. They can shape the structure of whole genomes and thus explain genome evolution to a large extent. Examples include the Homeobox genes in animals.
Passerines, the "song birds". This is the largest order of birds and contains more than half of all birds. Family Acanthisittidae. Genus Acanthisitta - rifleman; Genus Xenicus - New Zealand wrens; Family Acanthizidae - scrubwrens, thornbills, and gerygones Genus Acanthiza – thornbill; Genus Acanthornis – scrubtit; Genus Aethomyias ...