Molecular Basis Of Mutation: Mutation, Repair and Recombination
The Molecular Basis of Mutation explains changes in the DNA sequence. These mutations alter gene function and drive genetic variation. In Mutation NEET Biology, the molecular basis of mutation is linked to DNA replication errors, tautomeric shifts in DNA or exposure to external mutagens. There are types of mutations, like spontaneous mutations and induced mutations. Spontaneous mutations occur due to the DNA polymerase errors or tautomeric transitions. Induced mutations happen when DNA is exposed to an external mutagen, such as UV radiation, which induces thymine dimers and alkylating agents.
This Story also Contains
- Molecular Basis of Mutation in NEET Biology
- Definition of Gene Mutation with Example
- Types of Mutations
- Spontaneous Mutations vs Induced Mutations
- Mutation NEET MCQs (With Answers & Explanations)
- Recommended Video on Molecular Basis of Mutation
Errors in the mutation mechanism in replication of DNA or mutagens exposure lead to point mutation, transition, transversion, and frameshift mutations. A gene mutation definition includes permanent changes such as substitution, insertion, deletion, and frameshift mutation. These mutations cause protein sequence alteration and may result in frameshift mutation consequences. The molecular basis of mutation is vital in Mutation NEET Biology notes, covering spontaneous mutations vs induced mutations, DNA replication errors, tautomeric shifts in DNA, and mutagens like UV radiation, thymine dimers, and alkylating agents.
Molecular Basis of Mutation in NEET Biology
The molecular basis of mutation is changes in the nucleotide sequence of DNA that alters of the genetic information it carries. These can be caused by spontaneous errors during DNA replication, by chemicals, radiation, and also by viruses. The results of mutations can be innocuous or injurious and can moreover influence the attributes of an organism, thus attaining genetic diversity in populations or genetic disorders.
Also Read:
Definition of Gene Mutation with Example
A gene mutation is a permanent alteration within the DNA sequence that makes up the gene. Such mutations can happen in several ways, such as substitutions, insertions, deletions, and frameshift mutations. These changes can perturb gene function in a way that the expression of either a nonfunctional gene occurs or its production. Gene mutations are either inherited or acquired during an organism's lifetime and may make important contributions to a variety of diseases and evolutionary processes.
Types of Mutations
Mutations can be classified according to the nature of the change in the DNA sequence. All 4 types of mutation, along with their comparison, are discussed below in the table:
Feature | Substitution (Transition & Transversion) | Insertion | Deletion | Frameshift Mutation |
|---|---|---|---|---|
Definition | Another replaces one nucleotide | One or more nucleotides are added | One or more nucleotides are removed | Shifts the reading frame due to the insertion or deletion of nucleotides |
Sub-types | Transition (purine↔purine, pyrimidine↔pyrimidine); Transversion (purine↔pyrimidine) | Not applicable | Not applicable | Not applicable |
Effect on Reading Frame | No | Yes, if insertion is not in multiples of 3 | Yes, if deletion is not in multiples of 3 | Yes |
Impact on Protein Sequence | May be silent (no change), missense (amino acid change), or nonsense (stop codon) | Alters the amino acid sequence and can introduce a frameshift | Alters the amino acid sequence and can introduce a frameshift | Alters the entire downstream amino acid sequence |
Possibility of Frameshift | No | Yes, if not in multiples of 3 | Yes, if not in multiples of 3 | Always |
Functional Consequences | Protein may be normal, altered, or truncated | Protein may be non-functional or gain a novel function | May lead to loss of essential protein function | Usually results in non-functional or harmful proteins |
Severity of Effect | Mild to severe, depending on position and type | Often severe if it causes a frameshift | Often severe if it causes a frameshift | Usually severe due to a major change in protein structure |
Example | Sickle Cell Anaemia (missense mutation in β-globin gene) | Tay-Sachs disease (insertion in the HEXA gene) | Cystic Fibrosis (3-base pair deletion in the CFTR gene) | Huntington’s disease (triplet repeat expansion leads to a frameshift in the coding region) |
Spontaneous Mutations vs Induced Mutations
Mutations can be due to a variety of sources and can be broadly categorised into spontaneous and induced mutations. A basic comparison between spontaneous mutations and induced mutations is discussed below:
| Feature | Spontaneous Mutations | Induced Mutations |
|---|---|---|
Definition | Mutations that occur naturally without any external influence | Mutations that occur due to exposure to external physical, chemical, or biological agents (mutagens) |
Major Cause | Internal cellular processes (e.g., DNA replication errors, spontaneous base changes) | Environmental mutagens such as chemicals, radiation, or biological agents |
Sub-types | 1. Errors during DNA replication 2. Tautomeric shifts | 1. Chemical mutagens 2. Physical mutagens 3. Biological agents |
Mechanism |
|
|
Example of Mechanism |
|
|
Type of Mutation Caused | Often point mutations (e.g., transition or transversion) | Can cause point mutations, insertions, deletions, frameshifts, or chromosomal aberrations |
Repair Possibility | May be repaired by proofreading or mismatch repair systems | It may overwhelm repair systems, depending on the dose or intensity of the mutagen |
Examples |
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|
Significance | Source of natural genetic variation | Used in experimental mutagenesis and linked to mutagen-induced diseases (e.g., cancer) |
Mutation NEET MCQs (With Answers & Explanations)
Important questions asked in NEET from this topic are:
Classification and types of mutations
Causes and effects of mutations
Practice Questions for NEET
Question: What is not true for genetic code?
It is nearly universal
It is degenerate
It is unambiguous
A codon in mRNA is read in a non-contiguous fashion
Correct Answer: 4) A codon in mRNA is read in a non-contiguous fashion
Explanation:
DNA or mRNA sequences and amino acid sequences are connected through the genetic code, where each triplet of nucleotides, called a codon, encodes one of the 20 amino acids (e.g., glutamic acid, methionine, phenylalanine, serine, tryptophan, tyrosine, etc.). There are 64 codons in total, and the genetic code is read in a continuous and non-overlapping manner. The statement that codons are read in a "non-contiguous manner" is false, as codons are read sequentially without any spaces or interruptions between them. This continuous reading ensures that each codon is translated directly into an amino acid without any punctuation or gaps.
Hence, the correct answer is option 4) A codon in mRNA is read in a non-contiguous fashion
Question: A Transition or transversion mutation could result due to
Base pair mutation
Silent mutation
Nonsense mutation
Missense mutation
Correct Answer: 1) Base pair mutation
Explanation:
Mutations are changes in the DNA sequence that can affect gene expression and function. In addition to base-pair substitutions, mutations include insertion (addition of one or more nucleotides) and deletion (removal of nucleotides), which can cause frameshifts. Mutations can also be classified as silent, missense, or nonsense based on their impact on protein synthesis. These changes are significant in evolution, genetic disorders, and the understanding of cellular processes. Base-pair substitution is of two types:
Transition mutation: When one purine is replaced by another purine or one pyrimidine is replaced by another pyrimidine.
Transversion mutation: When one purine is replaced by a pyrimidine and vice versa.
Hence, the correct answer is option (1) Base pair mutation. .
Question: Which of the following is a type of gene mutation
Deletion
Addition
Substitution
All of these
Correct Answer: 4) All of them
Explanation:
Type of gene mutation:
Deletion: This is a type of mutation where one or more nucleotide bases are removed from the DNA sequence.
Addition: This is when one or more nucleotide bases are added to the DNA sequence.
Substitution: This occurs when one nucleotide base is replaced by another in the DNA sequence.
Hence, the correct answer is option 4)All of these
Also Read:
Recommended Video on Molecular Basis of Mutation
Frequently Asked Questions (FAQs)
The molecular basis of mutation in NEET Biology involves permanent DNA sequence changes caused by replication errors, tautomeric shifts, or mutagens like UV radiation, thymine dimers, and alkylating agents. These lead to point, substitution, insertion, deletion, and frameshift mutations, driving genetic variation or disorders.
Spontaneous mutations arise internally due to replication errors, while induced mutations result from external mutagens like radiation or chemicals.
Examples of gene mutations in humans include:
- Sickle Cell Anaemia: caused by a missense mutation in the β‑globin gene.
- Cystic Fibrosis: due to a deletion mutation in the CFTR gene.
- Tay‑Sachs Disease: insertion mutation in the HEXA gene.
- Huntington’s Disease: triplet repeat expansion leading to frameshift effects.
Mutations are changes in the DNA sequence that can alter protein function. Point mutations may be silent, missense, or nonsense, while insertions and deletions can cause frameshifts. Frameshift mutations usually disrupt the entire downstream sequence, often producing non‑functional or harmful proteins.
