| Summary: | The discovery of tetraploidy in the red viscacha rat, Tympanoctomys barrerae (4 n = 102) has emphasized the evolutionary role of genome duplication in mammals. The tetraploid status of this species is corroborated here by in situ PCR and Southern blot analysis of a single-copy gene. The species meiotic configuration strongly suggests a hybrid derivation. To investigate the origin of T. barrerae further, the recently described Pipanacoctomys aureus was studied. This 92-chromosome species also has a duplicated genome size, redundant gene copy number and diploid-like meiotic pairing, consistent with an event of allotetraploidization. Phylogenetic analysis of mitochondrial sequences indicates sister-group relationships between these two tetraploid rodents. The new karyotypic data and the phylogenetic relationships suggest the participation of the ancestral lineages of Octomys mimax in the genesis of P. aureus . The high overall DNA similarity and shared band homology revealed by genomic Southern hybridization as well as matching chromosome numbers between O. mimax and the descendant tetraploid species support the notion of introgressive hybridization between these taxa. Fil: Gallardo Narcisi, Milton Hermes. Universidad Austral de Chile; Chile Fil: Kausel, G. Universidad Austral de Chile; Chile Fil: Jiménez, A. Universidad Austral de Chile; Chile Fil: Bacquet, C. Universidad Austral de Chile; Chile Fil: González, C. Universidad Austral de Chile; Chile Fil: Figueroa, J. Universidad Austral de Chile; Chile Fil: Köhler, N. Universidad Austral de Chile; Chile Fil: Ojeda, Ricardo Alberto. Ministerio de Relaciones Exteriores, Comercio Internacional y Culto. Direccion Nacional del Antártico. Instituto Antártico Argentino. Instituto Antártico Argentino - Sede Cricyt (Mendoza); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de ...
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