Difference Between Substitution Insertion and Deletion Mutations

The key difference between substitution insertion and deletion mutations is their cause. Substitution mutations occur due to a substitution of a base pair from a different base pair, while insertion mutations occur due to the addition of extra nucleotides into a DNA sequence and deletion mutations occur due to the removing of one or more nucleotides from a DNA sequence.

A mutation is an alteration of the nucleotide sequence of DNA. A gene has a specific nucleotide sequence. Gene mutations can alter the genetic information hidden within its nucleotide sequence. The size of the mutation may vary from a single base change to a large fragment of a chromosome that contains multiple genes. Mutations occur due to various reasons. Some of the major reasons are mistakes occurring during the DNA copying in cell division, exposure to ionizing radiation, exposure to chemicals called mutagens and viral infections. Mutations are necessary for evolutions. Most mutations are harmless. Some mutations are heritable, affecting further descendants, while some mutations affect only the individual that carries them.

CONTENTS

1. Overview and Key Difference
2. What are Substitution Mutations
3. What are Insertion Mutations
4. What are Deletion Mutations
5. Similarities Between Substitution Insertion and Deletion Mutations
6. Side by Side Comparison – Substitution vs Insertion vs Deletion Mutations in Tabular Form
7. Summary

What are Substitution Mutations?

Substitution mutations are mutations that change base pairs of a nucleotide sequence with different base pairs. For example, a single base pair can be substituted into another base pair in the substitution mutation. They are called point mutations. The substitution may or may not give effects depending on the type of mutation. Silent mutation, missense mutation and nonsense mutation are three types of substitution mutations.

A silent mutation gives no outward effect though a substitution occurred. Substitution does not change the amino acid coded by the affected codon. Hence, it does not change the final protein. In missense mutation, substitution changes the amino acid coded by that particular codon. Sickle cell anemia is caused by a substitution in the beta-hemoglobin gene, which alters a single amino acid in the protein produced. In nonsense mutation, a base substitution transforms the affected codon into a stop codon, causing premature termination of translation. Generally, nonsense mutations produce non-functional or incomplete proteins.

What are Insertion Mutations?

Insertion mutations are mutations caused due to the addition of one or more nucleotides into a DNA sequence. Therefore, extra nucleotides are added to a DNA sequence in the insertion mutation. Similar to deletion mutations, insertion mutations can be small or large, depending on the number of base pairs added. In small insertions, a single base pair is generally added. Generally, in large insertion mutations, a small fragment of a chromosome is added newly.

Insertion of one base pair can cause a frameshift mutation changing the entire codon sequence. Insertion of three base pairs may be less harmful than the insertion of a single base pair. This is because three base pair insertion does not cause a frameshift mutation. Insertion of a large piece of DNA can be detrimental. If a stop codon is inserted accidentally during an insertion mutation, it leads to a premature end to translation resulting in a non-functional short protein.

What are Deletion Mutations?

Deletion mutations are mutations that occur due to removing a single nucleotide or entire sequences of nucleotides. Mostly they occur as a result of mistakes in the DNA replication process. Small deletions may range from one base pair to few nucleotides. Large deletions remove large fragments of DNA. Large deletions occur mostly during the crossing over.

Deletion mutations can be harmful or harmless. Basically, two factors determine the effect of the deletion mutation: where it happened and how many nucleotides are deleted. Generally, a single base pair deletion shifts the entire gene. It leads to a frameshift mutation which changes all of the original triplet codons producing a completely non-functional gene. Three or more nucleotides removing from a gene can result in a different amino acid sequence producing functional defects in the final protein. Some genetic diseases caused due to deletion mutations are male infertility, Duchenne muscular dystrophy, cystic fibrosis, Cri du chat syndrome and spinal muscular atrophy.

What are the Similarities Between Substitution Insertion and Deletion Mutations?

• Mutations can happen either by substitution, insertion or deletion.
• All these three types of mutations may be harmless or harmful.
• All three types change the original nucleotide sequence.
• They can cause genetic diseases.

What is the Difference Between Substitution Insertion and Deletion Mutations?

Substitution mutations are mutations in which a base pair is replaced by a different base pair. Insertion mutations are mutations in which one or more nucleotides are added into the DNA sequence. Deletion mutations are mutations in which one or more nucleotides are removed from the DNA sequence. So, this is the key difference between substitution insertion and deletion mutations. Moreover, a base pair is exchanged in a substitution mutation. But, exchanging of a base pair does not occur in insertion or deletion mutations. Besides, substitution mutations, generally, do not cause frameshift mutations, while both insertion and deletion mutations cause frameshift mutations.

Below is a summary of the difference between substitution insertion and deletion mutations in tabular form for side by side comparison.

Summary – Substitution vs Insertion vs Deletion Mutations

Substitution, insertion and deletion mutations are three types of mutations. A single base pair is replaced by another base pair in a substitution mutation. They may be silent, missense or nonsense mutations. But, one or more base pairs are added into the DNA sequence in insertion mutations. Meanwhile, one or more base pairs are removed from the DNA sequence in deletion mutations. Thus, this is the key difference between substitution insertion and deletion mutations.

Reference:

1. Loewe, L. (2008) Genetic mutation. Nature Education 1(1):113
2. Lodish, Harvey. “Mutations: Types and Causes.” Molecular Cell Biology. 4th Edition., U.S. National Library of Medicine, 1 Jan. 1970, Available here.

Image Courtesy:

1. “Point mutations-en” By Jonsta247 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Insertion-genetics” By National Human Genome Research Institute – (Public Domain) via Commons Wikimedia
3. “Deletion of chromosome section” By The original uploader was Mirmillon at French Wikipedia. – Vectorized from File: Deletion.gifNational Human Genome Research (USA)Originally from fr.Wikipedia; description page is/was here. (Public Domain) via Commons Wikimedia