Q.Write notes on Point or Gene mutation.
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Start your 14-day free trial to unlock the full solution →A point (gene) mutation is a change in one or a few base pairs of a gene's DNA, arising by substitution or insertion/deletion, with effects ranging from silent to disease-causing.
A point mutation (also called gene mutation) is a heritable change involving one or only a very few nucleotide base pairs within a single gene, as distinct from chromosomal aberrations, which involve changes in the structure or number of whole chromosomes.
Types, based on the change in the DNA sequence:
- Substitution -- one nucleotide base is replaced by another.
- Transition: a purine is replaced by another purine (A to G or G to A), or a pyrimidine by another pyrimidine (C to T or T to C).
- Transversion: a purine is replaced by a pyrimidine, or vice versa (e.g., A to C, G to T).
- Insertion -- one or more extra base pairs are added into the DNA sequence.
- Deletion -- one or more base pairs are lost from the DNA sequence.
Insertions and deletions (unless in multiples of three) shift the reading frame of the genetic code downstream of the mutation site, called a frameshift mutation, which usually garbles the entire amino acid sequence translated after that point.
Effect of substitution mutations on the protein product (since the genetic code is triplet and degenerate):
- Silent mutation -- the changed codon still codes for the same amino acid (due to the redundancy/degeneracy of the genetic code), so the protein is unaffected.
- Missense mutation -- the changed codon codes for a different amino acid, potentially altering protein structure/function. …
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