Molecular taxonomy uses nucleotide sequence data to determine evolutionary relationships between organisms. It involves comparing the sequences of homologous molecules from each organism to determine differences, with more differences indicating more distant relationships. Walter Zimmerman and Willi Hennig pioneered using objective criteria like shared genetic attributes to determine phylogenetic relationships. Advances in molecular biology techniques and computing power allowed modeling large datasets to further molecular systematics. It helps resolve taxonomic problems, reorganize the tree of life, and has medical applications like tracking disease evolution.

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
to determine the evolutionary relationships of different organisms
involves
comparing the sequences of functionally homologous molecules from each organism
to 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 physiologygeographic 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