Types of Mutations: Definition, Structure, Expression, Facts, Characteristics, Functions

Mutations are the sudden changes in DNA sequences of an organism. A Mutation in DNA can affect a single gene or even a large section of chromosomes. Gene Mutations occur in body cells or reproductive cells, which are passed to the next generation. Some chromosomal mutations can lead to visible genetic changes. Understanding mutations are important in the study of the genetic principle of heredity.

This Story also Contains

1. What Is Mutation?
2. Mutation Mechanisms
3. Classification Of Mutations
4. Types Of Mutations
5. The Video Recommended On Types Of Mutations:
6. MCQs on Types Of Mutations

The molecular basis of mutation is the change in DNA sequence caused by replication errors or mutagens. The effects of mutations can vary widely. Some genetic mutations are harmless, while others can be harmful too. It can lead to disorders like cancer. Mutations and evolution are closely linked, as mutations contribute to genetic diversity.

What Is Mutation?

A mutation is generally defined as any permanent change in the DNA sequence coding for a gene. This can add a change in the sequence of just a single DNA building block—a nucleotide—or several nucleotide pairs. It can be added to or removed from the DNA molecule. Mutagens are agents that increase the rate of mutations by altering the DNA structure. It involves large-scale chromosomal changes at the level of genes, including gene duplications and deletions, and chromosomal rearrangements. Any change in the genetic code and mutation can lead to altered or faulty proteins in the body.

Mutation Mechanisms

The mechanisms of genetic diversity and evolution can be understood only by studying mutations. Indeed, genetic mutations are the basis of evolution because they provide the required genetic variability on which natural selection works.

The mechanism of mutation refers to how changes occur in the DNA sequence. Mutations can happen due to errors in the replication of DNA, exposure to radiation, chemicals (mutagens), or viral infections. These factors can damage the DNA or cause incorrect copying of genetic information.

When the DNA repair system fails to correct these errors, the mutation becomes permanent in the cell. If mutations occur in germ cells, they can be passed to offspring. In somatic cells, mutations may lead to diseases like cancer. This mechanism is key to understanding genetic variation, evolution, and human genetic disorders.

Classification Of Mutations

Mutations can be classified based on their cause and the type of cells affected. These classifications help us understand how mutations arise and their impact on organisms. Mutations can be categorised based on their origin and also by the type of cells they affect.

Based On Origin

Spontaneous Mutations: These occur naturally, independent of any exogenous influence. It is caused by errors in processes like DNA replication or its repair. Although spontaneous mutation is a relatively rare event, it still can add up through time and so may lead to increased genetic diversity and evolution.

Induced Mutations: Due to external factors such as radiation, chemicals, or viruses, such mutations make up the bulk of induced mutations. In comparison with spontaneous mutation rates, induced mutations are more common and can be used in a laboratory setting to investigate gene function and regulation.

Based On Cell Type

Germline Mutation: This involves a mutation in the reproductive cells; that is, the structure of sperm and egg, hence transmissible to offspring. Germline mutations are important for the process of evolution because they lead to an increase in genetic variation within populations. They are also responsible for inherited genetic disorders.

Somatic Mutations: These are the mutations that occur in non-reproductive cells. Since they don't happen in the reproductive cells, they are not passed down to offspring. Somatic mutations can cause cancer and other diseases because they can make the cells grow and reproduce uncontrollably.

Types Of Mutations

Mutations can occur in different forms, affecting genes in various ways. The main types include point mutations, insertions, and deletions. The types of mutations are:

Point Mutations

Point mutations are changes in a single nucleotide pair of gene structure. They can have various effects depending on the nature of the substitution and its location in the gene. Types of Point Mutations:

Examples:

• Sickle Cell Anaemia: Caused by a missense mutation.

• Cystic Fibrosis: Caused by a nonsense mutation.

Insertions And Deletions Mutations

Insertions and deletions refer to the addition or removal of one or more pairs of nucleotides in the DNA.

Frameshift Mutations

InDels not in multiples of three nucleotides lead to a changed reading frame of the message and changes in the amino acid sequence massively downstream of the mutation.

Examples and Effects: Frameshift mutations can result in serious genetic disorders like Tay-Sachs disease, wherein their deletion causes a non-functional enzyme.

Chromosomal Mutations

Chromosomal mutations are larger in scale and have different structures of chromosomes, which can bring prominent effects on an organism. Types of chromosomal mutations:

Example:

• Chronic Myeloid Leukaemia (CML): Caused by a reciprocal translocation between chromosomes 9 and 22 (Philadelphia chromosome).

• Down Syndrome is caused by trisomy 21, an extra copy of chromosome 21.

• Cri-du-chat Syndrome: Caused by a deletion on chromosome 5.

The Video Recommended On Types Of Mutations:

MCQs on Types Of Mutations

Question: Choose the incorrect statement/s w.r.t mutation:

1) Somatic mutations are heritable.

2) Germinal mutations are heritable.

3) Spontaneous mutations can be caused due to X-rays.

4) A mutation always produces desirable effects

1. 1, 2, and 4

2. 2, 3, and 4

3. 1, 3, and 4

4. All of these

Mutations occurring in somatic cells are not heritable. X-rays can induce mutations, which can be harmful, beneficial, or have no effect. Point mutations and chromosomal abnormalities are the two main categories of mutations. A single base pair is altered in point mutations. Deletion, duplication, inversion, and translocation are examples of chromosomal abnormalities.

Hence, the correct answer is option (3) 1, 3, and 4

Question: Which of the following is a type of gene mutation

1. Deletion

2. Addition

3. Substitution

4. All of these

Answer: 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.

Question: A Transition or transversion mutation could result due to

1. Base pair mutation

2. Silent mutation

3. Nonsense mutation

4. Missense mutation

Answer: 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.

Also Read:

• Practice more on types of mutations

• Principles Of Inheritance And Variation

• Mendelian Genetics