Methods for comparing sequence data such as restriction endonuclease maps or nucleotide sequences of viral nucleic acid molecules.

Maps of restriction endonuclease sites in the DNA genomes of orthopoxviruses were compared by computer classification methods. Data from such maps were recorded as qualitative binary information, and gave closely similar dendrograms when different dissimilarity measures and sorting strategies were used for the computations. A method for calculating dendrograms from small data sets, by 'hand', is described in detail to assist those who do not have access to suitable computer programs. The same calculation strategy gave useful classifications of partial nucleotide and amino acid sequences of orthomyxovirus haemagglutinins.