What Are Mutations?

• Mutations are changes in the DNA sequence that can affect how genes function.
• Mutations can occur naturally or be caused by environmental factors like UV radiation or chemicals.
• Mutations may result in a change in protein structure, which can affect traits or lead to diseases.

Types of Mutations

Mutations can be classified into two main types based on their impact on the codons:

1. Point Mutations
   • Definition: A change in one single nucleotide of the DNA sequence.
   • Subtypes:
     • Substitution: One nucleotide is replaced with another.
       • Example: A → G (Adenine is replaced by Guanine).
       • Effect: Can lead to:
         • Silent mutation (no change to the protein).
         • Missense mutation (a different amino acid is produced).
         • Nonsense mutation (introduces a stop codon, shortening the protein).
     • Insertion: One or more nucleotides are added to the DNA sequence.
       • Example: A new nucleotide is added between two existing bases.
       • Effect: Insertion can sometimes lead to a frameshift, but if the change is small, it can still be considered a point mutation.
     • Deletion: One or more nucleotides are removed from the DNA sequence.
       • Example: One nucleotide is removed from the sequence.
       • Effect: Deletion can also cause a frameshift, but if it’s small, it’s considered a point mutation.
2. Frameshift Mutations
   • Definition: A mutation where insertions or deletions cause a shift in the reading frame of the codons.
   • Effect: This shifts the entire codon sequence, altering the protein from the point of mutation onward.
     • Insertion: Adding a base shifts the reading frame.
     • Deletion: Removing a base shifts the reading frame.
   • Impact: Frameshift mutations almost always lead to severe changes in the protein’s structure and function.

Types of Mutations Based on Their Effect on the Protein:

1. Silent Mutation:
   • Definition: A mutation that does not affect the protein because the new codon still codes for the same amino acid.
   • Example: A change in DNA that results in the same amino acid being added to the protein.
2. Missense Mutation:
   • Definition: A mutation that results in a different amino acid being incorporated into the protein.
   • Effect: The protein may function differently, or in some cases, may be nonfunctional.
   • Example: Sickle cell disease is caused by a missense mutation in the hemoglobin gene.
3. Nonsense Mutation:
   • Definition: A mutation that causes an early stop codon, leading to a truncated (shortened) protein.
   • Effect: The protein is often nonfunctional or incomplete.
   • Example: A mutation in a gene that causes cystic fibrosis can be caused by a nonsense mutation.

Causes of Mutations

Type of Cause	Examples
Spontaneous Mutations	Errors during DNA replication or repair.
Induced Mutations	Environmental factors like UV light, chemicals, or radiation.

Effects of Mutations

Type of Effect	Description
Neutral Mutation	No effect on the organism or protein.
Beneficial Mutation	Provides an advantage (e.g., resistance to a disease).
Harmful Mutation	Causes disease or dysfunction (e.g., cancer, genetic disorders).

Mutation in the Context of Evolution

• Mutations are a key source of genetic variation in populations.
• Beneficial mutations can be selected for over generations, leading to evolution.

🎯 Pro Tip

• Point Mutations = Small changes in the DNA sequence (Substitution, Insertion, Deletion).
• Frameshift Mutations = Larger changes that shift the codon reading frame (Insertions and Deletions).
• Silent, Missense, and Nonsense = Based on how the mutation impacts the protein structure.

Written by Kasiban Parthipan