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Bacterial Numerical / Adansonian Taxonomy by Micheal Adanson

	In the 19th century, microorganisms were grouped according to, their evolutionary affinities and the arrangement of organisms into groups was on the basis of inherited and stable structural and physiological characters. This arrangement is known as the Natural or the Phylogenetic classification. This approach, of classifying microorganisms is now almost abandoned in favour of a more empirical approach based on quantification of similarities and differences among organisms. This approach was first suggested by Micheal Adanson and is known as Adansonian or Numerical taxonomy.
The basis of this approach is the assumption that when each phenotypic character is given equal weightage, then it should be possible to express numerically the taxonomic distances between organisms in terms of the number of characters that are shared relative to the total number of characters examined. The significance of this taxonomy is greatly influenced by the number of characters examined. To obtain a high degree of significance therefore, a large number of characters have to examined.
The determination of similarity coefficient and matching coefficient for two bacterial strains, both characterized with respect to many different characters a, b, c, d, etc. can be determined as follows Number of characters positive in both strains = a Number of characters positive in strain 1 and negative in strain 2 = b Number of characters negative in strain 1 and positive in strain 2 = c Number of characters negative in both strains = d Similarity coefficient (Sj) = a / a+b+c Matching coefficient (Ss) = a+b / a+b+c+d
The similarity coefficient does not take into account the characters negative for both organisms while the matching coefficient includes both positive an negative characters. After similatiry coefficient and matching coefficient are determined for all organisms under study pair wise, the data are arranged in similarity matrix. Such matrices can be reordered to bring similar strains close to one another. Such data are then transposed to a dandrogram. As the basis for determining taxonomic arrangements.
	The dotted lines in a dandrogram indicate similarity levels which might be considered for recognizing two different taxonomic ranks such as a genus and a species. Earlier, the Adansonian approach appeared impractical because of the magnitude of numerical operations involved. This difficulty has now been overcome by the use of computers which can be programmed to compute the data and determine the degree of similarity. Although numerical taxonomy does not show any phylogenetic relationship, yet, it provides a stable basis for the construction of taxonomic groupings.

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