Evolution of karyotype,sex chromosomes,and meiosis in mygalomorph spiders (Araneae: Mygalomorphae) |
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Authors: | Jiří Král Tereza Kořínková Lenka Krkavcová Jana Musilová Martin Forman Ivalú M. Ávila Herrera Charles R. Haddad Magda Vítková Sergio Henriques José G. Palacios Vargas Marshal Hedin |
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Affiliation: | 1. Laboratory of Arachnid Cytogenetics, Department of Genetics and Microbiology, Faculty of Science, Charles University in Prague, , CZ‐128 44 Prague 2, Czech Republic;2. Department of Zoology and Entomology, University of the Free State, , Bloemfontein, 9300 South Africa;3. Faculty of Science, University of South Bohemia, , CZ‐370 05 ?eské Budějovice, Czech Republic;4. Department of Molecular Biology and Genetics, Institute of Entomology, Biology Centre ASCR, , CZ‐370 05 ?eské Budějovice, Czech Republic;5. Centro de Investiga??o em Biodiversidade e Recursos Genéticos, Campus Agrário de Vair?o, , P‐4485‐661 Vila do Conde, Portugal;6. Departamento de Ecología y Recursos Naturales, Universidad Nacional Autónoma de México, Facultad de Ciencias, Ciudad Universitaria, , C. P. 04510 México;7. Department of Biology, San Diego State University, , San Diego, CA, 92182‐4614 USA |
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Abstract: | Spider diversity is partitioned into three primary clades, namely Mesothelae, Mygalomorphae, and Araneomorphae. Mygalomorph cytogenetics is largely unknown. Our study revealed a remarkable karyotype diversity of mygalomorphs. Unlike araneomorphs, they show no general trend towards a decrease of 2n, as the chromosome number was reduced in some lineages and increased in others. A biarmed karyotype is a symplesiomorphy of mygalomorphs and araneomorphs. Male meiosis of some mygalomorphs is achiasmatic, or includes the diffuse stage. The sex chromosome system X1X20, which is supposedly ancestral in spiders, is uncommon in mygalomorphs. Many mygalomorphs exhibit more than two (and up to 13) X chromosomes in males. The evolution of X chromosomes proceeded via the duplication of chromosomes, fissions, X–X, and X‐autosome fusions. Spiders also exhibit a homomorphic sex chromosome pair. In the germline of mygalomorph males these chromosomes are often deactivated; their deactivation and pairing is initiated already at spermatogonia. Remarkably, pairing of sex chromosomes in mygalomorph females is also initiated at gonial cells. Some mygalomorphs have two sex chromosome pairs. The second pair presumably arose in early‐diverging mygalomorphs, probably via genome duplication. The unique behaviour of spider sex chromosomes in the germline may promote meiotic pairing of homologous sex chromosomes and structural differentiation of their duplicates, as well as the establishment of polyploid genomes. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 377–408. |
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Keywords: | achiasmatic chromosome pairing deactivation duplication heterochromatinization NOR polyploidy |
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