INTRA-SPECIFIC AND INTERSPECIFIC DNA VARIATION AND CODON BIAS OF THE ALCOHOL-DEHYDROGENASE (ADH) LOCUS IN ARABIS AND ARABIDOPSIS SPECIES

Sequence variation at the alcohol dehydrogenase (Adh) locus was analyz ed for six species each of the genera Arabis and Arabidopsis. Phylogen etic analysis showed that investigated species were grouped into three clusters, and the generic classification did not correspond to the cl usterings. The results indicated that the genera could not be distingu ished on the basis of the Adh variation. A significant difference in t he ratio of silent to replacement sites was detected by MK test in two comparisons, with Arabidopsis thaliana polymorphism due to excess sil ent divergence. Silent changes were predominant in the evolution of th e Adh locus in Arabis and Arabidopsis. To infer evolutionary significa nce of silent substitutions, codon bias was studied. The degree of cod on bias of the Adh region was relatively constant over Arabis and Arab idopsis species. ''Preferred'' codons of A. thaliana were determined. No evidence of natural selection on codon change was detected in the A dh regions of A. thaliana and Arabis gemmifera.