Mutations

Introduction to Mutations

Definition

Mutations are alterations or changes in the DNA sequence of an organism. These changes can affect the structure and function of proteins encoded by the affected genes.

Types of Mutations

Mutations can be classified into various types, including point mutations, insertions, deletions, and chromosomal mutations.

Point Mutations

Definition

Point mutations involve changes in a single nucleotide base within the DNA sequence.

Types of Point Mutations

• Substitution: A single base is replaced by another. For example, a substitution mutation may change the DNA sequence from ATG to ACG.
• Transition: A purine base (A or G) is replaced by another purine, or a pyrimidine base (C or T) is replaced by another pyrimidine. For example, a transition mutation may change the DNA sequence from ATG to ACG.
• Transversion: A purine is replaced by a pyrimidine or vice versa. For example, a transversion mutation may change the DNA sequence from ATG to CTG.

Insertions and Deletions (Indels)

Definition

Insertions involve the addition of one or more nucleotide bases into the DNA sequence, while deletions involve the removal of one or more nucleotide bases.

Frameshift Mutations

Insertions and deletions often lead to frameshift mutations, where the reading frame of the gene is shifted, resulting in a completely different amino acid sequence downstream.

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Mutations

Chromosomal Mutations

Definition

Chromosomal mutations involve changes in the structure or number of whole chromosomes.

Types of Chromosomal Mutations

• Deletion: A portion of a chromosome is lost or deleted.
• Duplication: A section of a chromosome is duplicated, leading to extra genetic material.
• Inversion: A portion of a chromosome is reversed in orientation.
• Translocation: A segment of one chromosome is transferred to another non-homologous chromosome.

Consequences of Mutations

1. No Protein or Altered Protein

Mutations can result in the absence of a protein or the synthesis of an altered protein. The impact on protein function depends on the type and location of the mutation.

2. Silent Mutations

Some point mutations do not change the amino acid sequence due to the degeneracy of the genetic code. These are known as silent mutations.

3. Missense Mutations

Missense mutations result in a change in one amino acid in the protein. The effect on protein function depends on the specific amino acid substitution.

4. Nonsense Mutations

Nonsense mutations introduce a premature stop codon into the mRNA sequence, leading to the early termination of protein synthesis.

Importance of Mutations

Genetic Variation

Mutations are a source of genetic variation within populations, which is essential for evolution and adaptation to changing environments.

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Mutations

Disease

Mutations can lead to genetic diseases and disorders, such as cancer, cystic fibrosis, and muscular dystrophy.

Examples of Mutations

Sickle Cell Anaemia

Sickle cell anaemia is caused by a point mutation in the HBB gene, which encodes haemoglobin. In this mutation, a single base substitution leads to the replacement of glutamic acid with valine in the haemoglobin protein. This change alters the shape of red blood cells, leading to their characteristic sickle shape and causing health problems.

Cystic Fibrosis

Cystic fibrosis results from mutations in the CFTR gene. Various mutations can affect the function of the CFTR protein, which plays a role in ion transport across cell membranes. Mutations in this gene lead to the production of defective CFTR proteins, causing thick mucus to accumulate in the respiratory and digestive systems.

Summary