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Open Access Research article

Halibut mitochondrial genomes contain extensive heteroplasmic tandem repeat arrays involved in DNA recombination

Kenneth A Mjelle1, Bård O Karlsen1, Tor E Jørgensen1, Truls Moum1 and Steinar D Johansen12*

Author Affiliations

1 Department of Fisheries and Natural Sciences, Bodø University College, N-8049 Bodø, Norway

2 Department of Molecular Biotechnology, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway

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BMC Genomics 2008, 9:10  doi:10.1186/1471-2164-9-10

Published: 11 January 2008

Abstract

Background

Halibuts are commercially important flatfish species confined to the North Pacific and North Atlantic Oceans. We have determined the complete mitochondrial genome sequences of four specimens each of Atlantic halibut (Hippoglossus hippoglossus), Pacific halibut (Hippoglossus stenolepis) and Greenland halibut (Reinhardtius hippoglossoides), and assessed the nucleotide variability within and between species.

Results

About 100 variable positions were identified within the four specimens in each halibut species, with the control regions as the most variable parts of the genomes (10 times that of the mitochondrial ribosomal DNA). Due to tandem repeat arrays, the control regions have unusually large sizes compared to most vertebrate mtDNAs. The arrays are highly heteroplasmic in size and consist mainly of different variants of a 61-bp motif. Halibut mitochondrial genomes lacking arrays were also detected.

Conclusion

The complexity, distribution, and biological role of the heteroplasmic tandem repeat arrays in halibut mitochondrial control regions are discussed. We conclude that the most plausible explanation for array maintenance includes both the slipped-strand mispairing and DNA recombination mechanisms.