Discus study shows unique chromosomes

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Scientists examining the chromosomes of three Discus species have found that two of the have features that were previously unseen in vertebrates.

The study, which is due to be published shortly in the journal Heredity, provides evidence to suggest that Symphysodon aequifasciatus and S. haraldi have "an intriguing meiotic chromosomal chain", which is the first ever seen in a fish or other vertebrate.

The condition is not present in the chromosomes of Symphysodon discus, further demonstrating that this is a completely distinct species.

The authors said: "We have confirmed that Symphysodon species are characterized by chromosomal diversity and meiotic complexity despite the fact that species share the same diploid number 2n=60.

"An intriguing meiotic chromosomal chain, with up to 20 elements during diplotene/diakinesis, was observed in S. aequifasciatus and S. haraldi, whereas S. discus only contains typical bivalent chromosomes."

"This observation is unusual and we propose that the origin of meiotic multiples in males and females is based on a series of translocations that involved heterochromatic regions after hybridization of ancestor wild Discus species."

For more information see the paper: Gross MC, Feldberg E, Cella DM, Schneider MC, Schneider CH, Porto JI, Martins C (2009) - Heredity. 2009 Feb 25, doi:10.1038/hdy.2009.3.