TYPES OF TAXONOMY​ – CHEMOTAXONOMY, CYTOTAXONOMY AND MOLECULAR TAXONOMY​

Introduction

Taxonomy in Science and method of naming organisms is a fundamental basis for all biological Science and its application . The principal task of taxonomy is to describe , establish and give an account of the order that is an inherent property of biological diversity .

The order of names provided by taxonomy is arranged as a hiearchial classification , which is considered to potray the hiearchy of species and more inclusive taxa as a result of the continuous chain of species splitting in the evolutionary history of life on earth . Generalizations on organisms as a basic principle in biology are only possible if the infinite number of items in Science is classified statements about the overwhelming diversity of nature would be impossible without methods for bringing order to this diversity .

The world’s biota is a vast library of information concerning any aspect of life and taxonomy is the cataloguing system that everybody must use to access its information .All kinds of biological Science and application link their specific data to species names and use these names for effective communication.

Types of taxonomy

Chemotaxonomy

Chemotaxonomy, also called chemosystematics, is to classify and identify organisms according to confirmable differences and similarities in their biochemical compositions. In a nutshell, the biological classification of plants and animals based on similarities and differences in biochemical composition.

Chemotaxonomic Classification

The phenolics, alkaloids, terpenoids and non-protein amino acids, are the four important and widely exploited groups of compounds utilized for chemotaxonomic classification. The system of chemotaxonomic classification relies on the chemical similarity of taxon. Three broad categories of compounds are used in plant chemotaxonomy:primary metabolites, secondary metabolites and semantics.

• Primary metabolites : Primary metabolites are compounds that are involved in the fundamental metabolic pathways, which is utilized by the plant itself for growth and development, for example, citric acid used in Krebs cycle.

• Secondary metabolites : Secondary metabolites are the compounds that usually perform non-essential functions in the plants. They are used for protection and defense against predators and pathogens and performs non-vital functions. For example, alkaloids, phenolics, glucosinalates, amino acids.

• Semantics: Information carrying molecules like DNA, RNA, proteins.

Cytotaxonomy

It is the branch of biology dealing with the relationship and classification of organism using comparative studies of chromosomes.

The structure , number and behavior of chromosomes is of great value in taxonomy, with chromosome number being the most widely used and quoted character. Chromosome numbers are usually determined at mitosis and quoted as the diploid number(2n), unless dealing with a polyploidy series in which case the base number of chromosomes in the genome of the original haploid quoted.

Another useful taxonomic character is the position of the centromere. Meiotic behavior may show the heterozygosity of inversions. This may be constant for a taxon ,offering further taxonomic evidence .

The cytotaxonomy is more significant over physiological taxonomy because cytotaxonomy is dealing with the comparative study of chromosome and with this method minute variation among the individuals among the individuals can be detected. DNA are present in the chromosome and the variation in DNA are responsible for the variation among the individuals, species , genus and so on . The difference in physiological variation are too less among the individuals of same species and other higher taxa

Molecular Taxonomy

Molecular Taxonomy is the classification of organisms on the basis of the distribution and composition of chemical substances in them.

Molecular techniques in the field of biology have helped to establish genetic relationship between the members of different taxonomic categories. DNA and protein sequencing, immunological methods, DNA-DNA or DNA-RNA hybridization methods are more informative in the study of different species. The data obtained from such studies are used to construct phylogenetic trees.

Fitch and Margoliash ,(1967) made first phylogenetic tree based on molecular data. This tree was so close to the already established phylogenetic trees of the vertebrates that the taxonomists realized significance of molecular data and this made them understand that other traditional methods are although important but molecular evidences could be final or confirmatory evidences