Nucleolar chromosome variation and evolution in trie genusVicia

Abstract

SUMMARY — The nucleolar chromosomes in the genus Vicia usually comprise one or rarely two pairs of the complement in the diploid (2n = 10, 12, 14; x = 5, 6, 7) taxa. Barring V. anatolica nucleolar chromosomes in complements of various species have one secondary constriction and one satellite each. In V. anatolica (2n = 2x— 10) one of the two nucleolar chromosome pairs contained two secondary constrictions and two satellites. The nucleolar chromosomes in Vicia species show substantial variation, in satellite size from very minute to highly conspicuous, in the location of primary and secondary constrictions from terminal to mid region, and in the size of mid arm from very small to about 90 per cent of the total chromosome size. On the basis of proportionate size of the three stainable components, the nucleolar chromosomes in Vicia species have been classified into eighteen distinct types. The comparative morphology of the nucleolar chromosomes shows that interchanges including Robert-sonian fusion, deletion and/or inversion have mainly contributed to their divergence and evolution. Overall, the nucleolar chromosome variation showed a good correlation with the taxonomic classification. The present results provide probably the first example of an astonishing array of diversity in the form and shape of nucleolar chromosomes within a genus.