Single Gene Mutations

Introduction to Single Gene Mutations

Definition

Single gene mutations are alterations in the DNA nucleotide sequence of a single gene. These mutations can result from the substitution, insertion, or deletion of nucleotides within the gene.

Impact

Single gene mutations can have various effects on the encoded protein, ranging from no significant impact to the production of a non-functional protein.

Types of Single Gene Mutations

Missense Mutations:

• Definition: Missense mutations involve the substitution of one nucleotide for another, leading to the change of one amino acid in the encoded protein.
• Effect: Missense mutations can result in the production of a non-functional protein or have relatively little effect, depending on the specific amino acid substitution.

Nonsense Mutations

• Definition: Nonsense mutations lead to the premature creation of a stop codon within the gene sequence.
• Effect: This premature stop codon results in the production of a truncated and often non-functional protein.

Splice-Site Mutations

• Definition: Splice-site mutations affect the proper splicing of introns and exons during mRNA processing.
• Effect: These mutations can alter the protein's composition by retaining some introns or excluding certain exons from the mature mRNA transcript.

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Single Gene Mutations

Nucleotide Insertions or Deletions

Frame-shift Mutations

• Definition: Frame-shift mutations involve the insertion or deletion of one or more nucleotides, causing a shift in the reading frame of the gene.
• Effect: Frame-shift mutations have a profound impact on the protein's structure and function, often resulting in non-functional proteins.

Examples of Single Gene Mutations

1. Sickle-Cell Disease (Missense Mutation)

• Mutation: Sickle-cell disease results from a single base substitution in the HBB gene, altering haemoglobin.
• Effect: Altered haemoglobin leads to health problems, including reduced oxygen-carrying capacity.

2. Phenylketonuria (PKU) (Missense Mutation)

• Mutation: PKU is caused by mutations in the PAH gene, affecting phenylalanine metabolism.
• Effect: Elevated phenylalanine levels can lead to intellectual disabilities if not managed through diet.

3. Duchenne Muscular Dystrophy (Nonsense Mutation)

• Mutation: Duchenne muscular dystrophy results from mutations in the DMD gene, leading to truncated dystrophin protein.
• Effect: The absence of functional dystrophin causes progressive muscle degeneration.

Importance of Studying Single Gene Mutations

Medical Significance

Understanding single gene mutations is crucial for diagnosing, treating, and preventing genetic disorders.

Evolutionary Perspective

Mutations are a source of genetic diversity, playing a role in evolution and adaptation.

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Single Gene Mutations

Summary

Single gene mutations involve alterations in DNA nucleotide sequences and can have diverse effects on proteins. They include missense mutations (changing one amino acid), nonsense mutations (creating premature stop codons), splice-site mutations (affecting mRNA splicing), and frame-shift mutations (causing significant structural changes). Examples of genetic disorders resulting from these mutations include sickle-cell disease, phenylketonuria, and Duchenne muscular dystrophy. Studying these mutations is crucial for understanding genetic disorders and their medical implications.