Molecular taxonomy

Use of molecular genetics to study taxonomy

1. Molecular Taxonomy M.Raj Associate Professor Darrang College

2. “ The use of molecular genetics to study the evolution of relationships among individuals and species ”. Molecular Taxonomy uses nucleotide-sequence data t o determine the evolutionary relationships of different organisms involves comparing the sequences of functionally homologous molecules from each organism t o determine the number of differences between them The greater the number of differences, the more distantly related the organisms are likely to be.

3. Interest in phylogeny waned over much of the nineteenth century, replaced by an emphasis on genetics physiology geographic variances That began to change with the work of Botanist Walter Zimmerman 1940s Zoologist Willi Hennig 1950s and 1960s These scientists pioneered the definition of objective criteria for determining shared genetic attributes of living and fossil organisms

4. A revolution in molecular biology took place in the 1960s Methods for determining the molecular structure of proteins and amino acids allowed biologists to begin to estimate phylogenetic relationships The exponential growth of molecular systematics in the late twentieth century is due to increased sophistication in molecular biology techniques computer advances in hardware and software This allowed scientists to model large and complex data sets.

5. Tools of molecular taxonomy Molecular systematics uses a variety of techniques to derive phylogenetic trees. Polymerase chain reaction (PCR) is used to investigate variations of DNA on a large scale. Gene amplification is also fundamental to new approaches to DNA fingerprinting . Genetic markers are used to make inferences about relationships between environment and morphology, as well as physiology and behavior. DNA Bar Coding Chromosome painting

6. Applications of molecular taxonomy Species Tax. Problems Technique Amphiprion sebae Ratified taxonomic status RAPD Four species of clown fishes Revealed phylogenetic relationship RAPD Indian mackerel populations Revealed genetic homogeneity Multi-technique approach Dolphins, porpoise, whales & dugong Developed the capability of accurate identification mtDNA sequences. Helped in clearing up many taxonomical problems

7. Applications of molecular taxonomy Reorganization of the tree of life Carl Woese 1970s took on an ambitious project — determining the relationships of all life took advantage of a molecule that evolves extremely slowly — ( rDNA ) the DNA that encodes a small subunit of ribosomal RNA found that the sequences cluster in three groups corresponding to the eukaryotes ( Eukarya ), the archaea , and the eubacteria Three domain classification of the Living Organisms

8. Applications of molecular taxonomy Applications in medicine The ability to predict the course of evolution allows scientists to track epidemic pathogens research zootonic viruses understand the evolution of pharmaceuticals and drug resistance make predictions about emerging diseases This allows scientists to prepare vaccines for future strains in advance.

9. Advantages and Disadvantages Advantages: Using molecules is advantageous for the following two reasons: 1. Closer to the actual level of heredity (especially if you use DNA sequences). 2. The number of independently varying characters is huge. Each nucleotide position, in theory, can be considered a character and assumed independent. The DNA of any given organism has millions to billions of nucleotide positions. Disadvantages 1. Homoplasy (esp. reversals) are likely to occur at a higher rate in nucleotide sequences than in morphological characters (fewer states possible, no order of change, observed difference often smaller than actual accumulation of changes). 2. Homology among characters (esp. nucleotides) is sometimes not easily assessed (neighboring structures are simply more sequences) 3. They also have other obvious disadvantages: high cost and intensive training time