PHYLOGENETIC HIERARCHY, GENETIC CLASSIFICATION AND INTERSPECIES CLASSIFICATION

 PHYLOGENETIC HIERARCHY

·       Phylogenetics is the study of the ancestral relatedness of groups of organisms, whether alive or extinct.

·  A Phylogenetic tree is a diagram that represents evolutionary relationships among organisms. Phylogenetic trees are hypotheses, not definitive facts.

·       Phylogenetic Hierarchy implies that a group of organisms evolved from a common ancestor.

ü  Some of the information used to classify comes from fossils.

ü  Fossil evidence not available for most Prokaryotes.

ü  Phylogeny for Prokaryotes based on DNA Hybridization and rRNA Sequencing.

GENETIC CLASSIFICATION

·       Classification of organisms based on evolutionary as well as genetic relationship is known as Cladistics.

·       Cladistics is a method in which the organisms are classified using different criteria on the basis of the

ü  Evolution

ü  History

ü  Relationship between them.

·       The genetic relation help in identifying the Ancestors.

·       The tree which shows the evolutionary relationship between the organisms is known as the Cladogram.

·     Historically, Cladograms for vertebrates were made using fossil evidence. However, rRNA sequences are now being used to confirm assumptions based on fossils.

·   Most microorganisms do not leave fossils. Therefore, rRNA sequencing is primarily used to make cladograms for microorganism.

·     Cladistic methodologies involve the application of various molecular, anatomical, and genetic traits of organisms. Therefore, with the advent of Computational modelling and Molecular techniques (PCR).

·       Cladistics are often used in Evolutionary biology for the construction of Phylogenetic trees.

·       The small rRNA subunit used has 1500 bases, and computer programs do the calculations. The steps for constructing a Cladograms are

1)     rRNA sequences are aligned.

2)     The percentage of similarity between the sequences is calculated.

3)    Then the horizontal branches are drawn in a length proportional to the calculated percent similarity. All species beyond a node (branch point) have similar rRNA sequences, suggesting that they arose from an ancestor at that node.

INTERSPECIES CLASSIFICATION

·       Interspecies classification is a type of Classification which includes

a)     Biotype – Based on Biochemical characteristics

b)     Serotype – Based on Antigens in bacteria

c)     Phage type – Susceptibility to particular Phage

d)     Colicin type – Substance secreted by some bacteria

e)     Molecular typing – Plasmid profile and DNA Sequencing