Mutation refers to any change in the sequence of Nucleotides in DNA, which leads to changes in the genotype and phenotype of an organism. Mutations can be induced or spontaneous. Mutations can either be beneficial or harmful. Mutations lead to variation, which is one of the driving forces of evolution.
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Mutations occur due to deletion, insertion or substitution of one or more nucleotides. When a purine nucleotide is replaced by a purine nucleotide it is known as transition, and when a purine is replaced by a pyrimidine, it is known as transversion.
It is not necessary that every mutation leads to observable phenotypic changes. Mutations may be beneficial or harmful. Mutation is one of the main factors behind genetic variations on which natural selection operates. It can also lead to various diseases, e.g. sickle cell anaemia is caused due to point mutation. They even lead to cancer.
Spontaneous Mutation
Spontaneous mutations occur naturally in the genome. They generally occur due to error during replication, mitosis, meiosis, etc. Mutations may also occur due to mobile genetic elements or transposons. The main causes of spontaneous mutations are:
- Replication errors
- Slipped strand mispairing
- Wobble base pairing
- Depurination or deamination
- Tautomerism
- Unequal crossing over
Induced Mutation
Induced mutations do not occur spontaneously. They are induced through various chemical and physical agents known as mutagens. Mutagens greatly enhance the frequency of mutation.
Some of the mutagens are:
- Alkylating agents (Ethyl methanesulfonate or EMS, N-ethyl-N-nitrosourea or ENU)
- Base analogue (5-Bromouracil, Bromodeoxyuridine)
- Hydroxylamine modifies bases
- Deamination by nitrous acid
- DNA intercalating agents (ethidium bromide, proflavine)
- Oxidative damage (Reactive oxygen species, e.g. superoxide radical, hydrogen peroxide)
- Ionising and non-ionising radiations (gamma radiations, ultraviolet radiations, X-rays, etc.)
Difference between Spontaneous and Induced Mutation
The table below shows the main differences between Spontaneous and Induced Mutation.
|
Spontaneous Mutation |
Induced Mutation |
|
Spontaneous mutations occur naturally and mainly due to error in replication |
Induced mutations occur due to physical or chemical agents |
|
Occurs due to slippage in natural processes |
Induced by mutagens |
|
Caused due to replication error, tautomeric shift, transposable genetic elements, unequal cross overs, etc. |
Caused due to base modification, base analogues, intercalating agents, base mispairing, radiations, etc. |
|
E.g. sickle cell anaemia |
E.g. skin cancer due to prolonged exposure to radiations |
Frequently Asked Questions
What is spontaneous mutation?
Spontaneous mutations are naturally occurring alterations in the DNA due to slippage in natural processes. It mainly occurs due to errors in replication, transposable genetic elements, wobble base pairing, etc.
What are the different types of induced mutation?
​​Mutation can be induced by external mutagens such as chemical agents and radiation.
- Chemical agents – ethyl methanesulfonate (EMS), diethyl sulphate (DES), N-nitroso-N-ethyl urea (ENU), formaldehyde, ethidium bromide, etc.
- Radiations – X-rays, ultraviolet rays, gamma rays, alpha particles, beta particles, fast and thermal (slow) neutrons, etc.
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