Abstract
The chromosomes of Ostrea denselamellosa were studied using karyometric analysis, C-banding and silver-staining techniques. The karyotype consists of seven metacentric and three submetacentric chromosome pairs, identified as pairs 1, 2, 3, 5, 7, 8, 10 and 4, 6, 9, respectively. The constitutive heterochromatin (C-banding) was found in all cells studied as large centromeric heterochromatin blocks in pairs 6, 8, 9 and 10. The silver-stained nucleolus organizer regions ( Ag-NORs) were terminally located on the metacentric pairs 3 and 8. A variable number of one to three Ag-NOR chromosomes was observed within and between individuals, revealing a heteromorphism in the number of active NOR sites per cell. Nevertheless, the persistent occurrence of active NOR sites on at least one of the two homologous chromosomes in pairs 3 and 8 allows the identification of these pairs. In conclusion, our study has permitted the recognition of all the different chromosome pairs in Ostrea denselamellosa and has provided chromosome markers for use in future genetic manipulation.
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