What are Mutations? Types, Causes, Effects of Mutation

Mutation in biology is defined as sudden heritable changes in the DNA sequences. In other words, mutation is a change in the sequence of our DNA base pairs caused by numerous environmental stimuli such as UV light or mistakes during DNA replication. There are three types of mutation in biology known till date which forms the basis of evolution and genetic diversity.

Mutation in Biology

Mutations are essential for evolution to occur as they are the ultimate source of all new genetic material or new alleles in species. Majority of mutation in biology have no effect on the target organisms, some mutations are also beneficial. Let’s have a closer look on the types, causes, effects, and significance of mutation in biology class 12.

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Meaning of Mutation

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Each organism has its own DNA sequence. It can go through alteration in its base-pair sequence. It is known as a mutation. A mutation can cause alterations in proteins that are translated by the DNA. Cells can usually recognize and repair any damage caused by mutation before it becomes permanent. The primary causes of mutation in DNA sequences include: Error in DNA replication or Physical Exposure to mutagens or Viral Infections. 

Types of Mutation

For mutation to take place in genes or DNA, either natural or physical agents are required called mutagens. A mutagen is a substance that can bring about a permanent alteration to the physical structure of a DNA gene in such a way that the genetic message is changed.​

• Sickle cell anaemia, hemophilia, colourblindness are the diseases  caused by either gene or DNA mutations.
• Deoxyribonucleic acid or DNA forms the basis of mutation. 
• An individual or gene undergoing mutation is called a mutant.
• Germline mutations take place in the eggs and sperm and can be passed onto offspring.
• Somatic mutations take place in body cells and are not passed on. 
• The utilization of RNA by cell is immediately followed by RNA degradation.
• Thus, RNA or ribonucleic acids are less prone to any type of mutation in biology.

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Classification & Types of Mutations

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Several types of mutations are found in nature resulting from change in DNA sequences. The main categories for classification of mutation in biology includes:

1. Mutation Type Based on Cell

Somatic and germline mutations are the two types of mutations based on the cell type. They both differ in terms of inheritance, type of cell and time when sudden changes in chromosomes occur.

Somatic Mutation:

The type of mutations that takes place in somatic cells is called somatic mutations. Such alterations are also called acquired mutations. Somatic cells are incapable of passing mutations on to the next generation through reproduction.

Germline Mutation:

A type of mutation which occurs only in the germplasm of an organism is called germline mutations. Missense and nonsense mutations are the subtypes of germline mutations. Such mutations are passed on the offspring through the process of reproduction. Thus, germline mutations are also referred to as constitutional mutations. 

2. Mutation Type Based on DNA

The increase or decrease in the number of chromosomes is associated with several genetic disorders such as Down syndrome, Trisomy 13, etc. Such alterations in chromosomes are called chromosomal mutations.

Point mutation and frameshift mutation

Based on the change in the DNA sequences, two main types of mutations in biology are as follows: 

Point Mutation: 

When sudden change occurs in a particular and single nucleotide of a DNA segment, it is called point mutation. There are three types of mutations, which are as follows:

• Silent mutation: It refers to any change in DNA sequence that has no effect on the amino acid sequence in a protein or the functions that a protein performs. There is no observable phenotypic indication that a mutation has occurred.
• Nonsense mutation: When there is a change in the sequence of base pairs due to a point mutation, that results in a stop codon. This leads to a protein that is either shortened or non-functional.
• Missense mutation: A missense mutation occurs when a point mutation causes a change in the codon, which then codes for another amino acid.

Frameshift Mutation: 

A type of mutations that causes sudden change in the reading frame of DNA sequences is called frameshift mutation. Insertion, deletion and substitution are the sub-categories of frameshift mutations. 

• ​Substitution: The replacement of single nucleotides or amino acid sequences with others is associated with a type of mutation called substitution

• Insertion: The removal of one or more nucleotides from the complete DNA sequence is called deletion.

• Deletion: When one or more nucleotides are added to the existing DNA sequence, the type of mutation is called insertion.

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Causes of Mutation

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The mutation causes genetic diversification among the species. Positive mutations are transferred to successive generations. For example, sickle cell anemia is caused by a mutation in the gene coding for hemoglobin. The R.B.Cs take the shape of a sickle. However, in the African population, this mutation process provides protection against malaria. Moreover, cancer is caused by a mutation in the gene that controls cell division.

The mutation is caused by the following factors:

Internal Causes of Mutation

When DNA copies incorrectly, the majority of mutations occur. Evolution occurs as a result of all of these mutations. DNA makes a copy of itself during cell division. When a copy of DNA isn't flawless, it's called a mutation since it differs somewhat from the original DNA.

External Causes of Mutation

When certain chemicals or radiations are used to break down DNA, it causes the DNA to break down. The thymine dimers are broken by UV radiation, resulting in altered DNA.

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Effects of Mutation

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There are a number of mutations that cannot be transformed to the offsprings. These types of mutations occur in the somatic cells and are called somatic mutations. On the other hand, the germline mutations can be transformed to successive generations and occur in the reproductive cells. 

Significance of Mutation

1. Few mutations result in new protein versions, which aid organisms in adapting to environmental changes. Evolution occurs as a result of such mutations.
2. Antibiotic-resistant bacteria are strains of bacteria that can survive in the presence of antibiotics due to mutations in many bacteria.
3. A very unique mutation identified in the Italian population protects them from atherosclerosis, a condition in which fatty deposits build up in blood vessels.

Harmful Effects of Mutation

1. One or more genes can be mutated, resulting in genetic diseases. One such genetic illness is cystic fibrosis, which is caused by a mutation in one or more genes.
2. Another condition caused by mutations in genes that control the cell cycle is cancer.

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Things to Remember

• Over a lifetime, our DNA can undergo changes or mutations in the sequence of the bases, A , C, G and T.
• This can result in changes in the proteins that are made. This can be a bad or good thing. 
• Mutations can take place during DNA replication if errors are made and not rectified in time.
• Mutations can also take place due to the exposure to environmental factors like smoking, sunlight, radiation, 
• Mutations contribute to genetic variation within the species.
• Mutation can also disrupt normal gene activity and cause diseases like cancer.