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Point Mutation and Its Types

  • Category: Science
  • Subcategory: Genetics
  • Topic: DNA, Gene
  • Page: 1
  • Words: 599
  • Published: 26 October 2018
  • Downloads: 28
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Molecular basis of mutation

Any change in the DNA base sequence is known as the mutation. Some times this change may do not have a detectable phenotypic effect. A variety of different genetic forms can be observed as a mutational change in its nucleotide sequence. These mutational genetic forms of a gene are known as the alleles. Wild type allele of that gene is the form in which the given gene exists originally. Mutant alleles or mutants are the altered forms of the genes which are obtained due to mutations.

Types of mutations

Mutation is classified in two types. These are:

  1. Point mutation- It is base pair substitution. In this point mutation, an alteration takes place that changes only single base pair.
  2. Frame shift mutation- It is the insertion or deletion mutation. A single base or more than one base can be deleted or inserted by this type of mutation. It changes the reading frame.


Intercalating agents like acridine dye (acridine orange or proflavin) cause this frame shift mutation. A planner structure is possessed by them. Intercalation of those agents between the bases of the DNA double helix is observed. Because of this reason, the double helix structure gets distorted. Distortion of the structure can be obtained either by the insertion of some bases within the DNA sequence or by some deletion of bases from the DNA sequences and causes frame shift mutation. During replication, the distance between two consecutive base pairs is doubled by the intercalation of such dye between them.


In point mutation, transition and transversion are observed. Transition- (a) Purine to Purine or (b) Pyrimidine to Pyrimidine. Transversion- (a) Purine to Pyrimidine or (b) Pyrimidine to Purine Or Each pair of the base is able to undergo one kind of transition and two kinds of transversion.

Classification of point mutation

There are three types of point mutation can be obtained. These are as follows:

  1. Silent mutation or nutral mutation
  2. Missense mutation
  3. Nonsense mutation


It is also known as nutral mutation. Silent mutation is a type of mutation which does not possess any effect on protein synthesis. From the above figure we can see that, the amino acid remain the same inspite of the change in the DNA base sequence. This event results in no such detectable effect on the protein synthesis due to the degeneracy of the code. This is the biological importance of degeneracy of the code.


In case of missense mutation, a change in the amino acid is observed by the alteration of DNA base sequence. But this change is not observed at the active site of the protein. As a result, there is no effect on the protein activity due to this mutation. The mutation does not change the three dimensional protein structure. This results in no loss of activity of protein.

In the above figure, we can see that, the structure of the protein is changed. But this change is not at the active centre of the protein. Due to this reason, the activity of the protein remains the same. Another case may takes place in the missense mutation. In this case, the single amino acid replacement is observed at the active centre of the protein. This changed protein possesses some biological activity like the original one. Some times, this type of mutation fails to function at higher than the normal temperatures. This is known as the temperature sensitive mutations. As for example: Sickle cell anemia.

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