Trends of karyological evolution in Pelobatoid frogs

“…Microchromosomes are characteristic of all avian and many reptilian karyotypes, with the notable exception of the Crocodylia, a lineage phylogenetically closest to birds with a common ancestor 254 million years ago (Mya) (Janke and Arnason, 1997). Microchromosomes are also present in the karyotypes of many primitive vertebrates (Ohno et al, 1969;Morescalchi et al, 1977aMorescalchi et al, , 1977bMorescalchi et al, , 1979. These observations have led to the hypothesis that avian microchromosomes may represent archaic linkage groups of ancestral vertebrates (Tegelström and Ryttman, 1981;Jones et al, 1997;Fillon, 1998).…”

mentioning

confidence: 99%

Origin and evolution of avian microchromosomes

Burt¹

2002

Cytogenet Genome Res

225

262

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The origin of avian microchromosomes has long been the subject of much speculation and debate. Microchromosomes are a universal characteristic of all avian species and many reptilian karyotypes. The typical avian karyotype contains about 40 pairs of chromosomes and usually 30 pairs of small to tiny microchromosomes. This characteristic karyotype probably evolved 100–250 million years ago. Once the microchromosomes were thought to be a non-essential component of the avian genome. Recent work has shown that even though these chromosomes represent only 25% of the genome; they encode 50% of the genes. Contrary to popular belief, microchromosomes are present in a wide range of vertebrate classes, spanning 400–450 million years of evolutionary history. In this paper, comparative gene mapping between the genomes of chicken, human, mouse and zebrafish, has been used to investigate the origin and evolution of avian microchromosomes during this period. This analysis reveals evidence for four ancient syntenies conserved in fish, birds and mammals for over 400 million years. More than half, if not all, microchromosomes may represent ancestral syntenies and at least ten avian microchromosomes are the product of chromosome fission. Birds have one of the smallest genomes of any terrestrial vertebrate. This is likely to be the product of an evolutionary process that minimizes the DNA content (mostly through the number of repeats) and maximizes the recombination rate of microchromosomes. Through this process the properties (GC content, DNA and repeat content, gene density and recombination rate) of microchromosomes and macrochromosomes have diverged to create distinct chromosome types. An ancestral genome for birds likely had a small genome, low in repeats and a karyotype with microchromosomes. A “Fission–Fusion Model” of microchromosome evolution based on chromosome rearrangement and minimization of repeat content is discussed.

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“…We note as well that most of the bird species show a typical karyotype with around 60 microchromosomes, although the Accipitridae have only three to six pairs of microchromosomes [22,23,24]. In Ciconiiformes, there is an important reduction in the number of chromosomes (50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60) [49]. In reptiles, fish and amphibians, hybridization signals were also found in pericentromeric or interstitial regions for some species [50].…”

Section: The Evolutionary Meaning Of Microchromosomesmentioning

confidence: 56%

“…Indeed, they could have been inherited from a common ancestor of the vertebrates, as they can be encountered in primitive orders such as cartilaginous fish [59,75], salamanders [55] or monotreme [79]. Moreover [54]. In reptiles [48,64,76] and amphibians [55], only a small number of chromosomes can be thought to be microchromosomes.…”

Section: The Evolutionary Meaning Of Microchromosomesmentioning

confidence: 99%

The chicken as a model to study microchromosomes in birds: a review

Fillon¹

1998

Genet. Sel. Evol.

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Trends of karyological evolution in Pelobatoid frogs

Cited by 22 publications

References 5 publications

Karyotypes of eight species of Leptodactylus (Anura, Leptodactylidae) with a description of a new karyotype for the genus

Karyotypes of eight species of Leptodactylus (Anura, Leptodactylidae) with a description of a new karyotype for the genus

Origin and evolution of avian microchromosomes

The chicken as a model to study microchromosomes in birds: a review

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