Introduction to Mutation

-Mutation is spontaneous and random change to genetic contents of an organism or cells.
-New Genetic materials produced by mutations are called mutants, which can exist as mutant genes, mutant organelles or mutant organism.
-Only mutation occurring in gamate cells can be inherited.


Spontaneous Mutation is a mutation that occurs naturally. It's rate is very low.


Induced mutation is caused by mutagens.
-Mutagens are substances tha cause mutations or increase mutation rate.
-Mutagens are classified into 2 groups: Chemical and Physical mutagens.

1. Chemical mutagens:
-Chemical Modifications of Purine and Pyrimidine bases by altering their hydrogen bonding properties. Eg: Nitrous acid converts cytosine to uracil.
-Base Analogs - chemically resemble a nucleotide base - can be incorporated into the place of natural base in DNA during DNA replication.
-Prevents formation of Spindle Fibres -Colchicine.

2. Physical Mutagens:
-Ultraviolet radiation - causes adjacent Thymine bases on the same DNA strand to covalently bond together.
-Ionizing radiation - ionizes molecules to form radicals - can break DNA and alter purine and pyrimidine bases.