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      Gametogenesis and nucleotypic effects in the tetraploid red vizcacha rat, Tympanoctomys barrerae (Rodentia, Octodontidae)

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          Nucleotypic effects link DNA content with nuclear size and cell dimensions of reproductive cells in polyploid organisms. We studied the gametogenesis of the allotetraploid rodent Tympanoctomys barrerae, aiming to determine these effects in reproductive cells. The species' cofamily members, Octodon degus and Spalacopus cyanus were used as control. Spermatogenesis and oogenesis in T. barrerae follows the pattern of differentiation and sequence of events of the control species, but varied nucleotypic effects were observed. Exceedingly large, spatulated spermatozoa with a submedially attached flagellum are characteristic of male T. barrerae. The diameter of the nuclei of primordial and growing follicles as well as those of the Graaff follicles, of the granulose, and of luteal cells are significantly larger and heavily heterochromatic. Moreover, the width of the pellucid zone is 108% thicker in T. barrerae than in S. cyanus. Binucleation was recorded in 26% of luteal bodies examined whereas no binucleated cells are detected in the diploid control. Likewise, large heterochromatic nucleoli were observed in the follicle cells but not in S. cyanus. This finding and the high heterochromatin content of reproductive cells in the red vizcacha rat is probably associated with its genome complexity so that redundant genetic information is silenced through heterochromatinization

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          Most cited references 44

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          Yesterday's polyploids and the mystery of diploidization.

           Mary K Wolfe (2001)
          Thirty years after Susumu Ohno proposed that vertebrate genomes are degenerate polyploids, the extent to which genome duplication contributed to the evolution of the vertebrate genome, if at all, is still uncertain. Sequence-level studies on model organisms whose genomes show clearer evidence of ancient polyploidy are invaluable because they indicate what the evolutionary products of genome duplication can look like. The greatest mystery is the molecular basis of diploidization, the evolutionary process by which a polyploid genome turns into a diploid one.
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            Chromosomal evolution in higher plants

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              Genetic and epigenetic interactions in allopolyploid plants.

               L Comai (2000)
              Allopolyploid plants are hybrids that contain two copies of the genome from each parent. Whereas wild and cultivated allopolyploids are well adapted, man-made allopolyploids are typically unstable, displaying homeotic transformation and lethality as well as chromosomal rearrangements and changes in the number and distribution of repeated DNA sequences within heterochromatin. Large increases in the length of some chromosomes has been documented in allopolyploid hybrids and could be caused by the activation of dormant retrotransposons, as shown to be the case in marsupial hybrids. Synthetic (man-made) allotetraploids of Arabidopsis exhibit rapid changes in gene regulation, including gene silencing. These regulatory abnormalities could derive from ploidy changes and/or incompatible interactions between parental genomes, although comparison of auto- and allopolyploids suggests that intergenomic incompatibilities play the major role. Models to explain intergenomic incompatibilities incorporate both genetic and epigenetic mechanisms. In one model, the activation of heterochromatic transposons (McClintock's genomic shock) may lead to widespread perturbation of gene expression, perhaps by a silencing interaction between activated transposons and euchromatic genes. Qualitatively similar responses, of lesser intensity, may occur in intraspecific hybrids. Therefore, insight into genome function gained from the study of allopolyploidy may be applicable to hybrids of any type and may even elucidate positive interactions, such as those responsible for hybrid vigor.

                Author and article information

                Role: ND
                Role: ND
                Role: ND
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                Biological Research
                Biol. Res.
                Sociedad de Biología de Chile (Santiago )
                : 37
                : 4 suppl A
                : 765-775
                [1 ] Instituto de Ecología y Evolución
                [2 ] Universidad Austral de Chile Chile
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