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Nature. 1999 Sep 23;401(6751):341.
Discovery of tetraploidy in a mammal.
Gallardo MH, Bickham JW, Honeycutt RL, Ojeda RA, Kohler N.
Instituto de Ecologia y Evolucion, Universidad Austral de Chile, Valdivia. mgallard@uach.cl
"Nevertheless, genetic evidence indicates that the red viscacha rat, Tympanoctomys barrerae (Octodontidae), is tetraploid. T. barrerae, which is a highly specialized desert rodent, has the largest chromosome complement in mammals with a single XY sex-chromosome system (Fig. 1). Although little is known about meiotic chromosome pairing in T. barrerae, the constant diploid number found in 13 specimens examined at three localities in Argentina indicates that segregation occurs normally."
PMID: 10517628
If you can access the article they have a great comparative figure showing that the tetraploid rat has enormous sperm to accommodate the extra DNA.
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