Gene Mutations Overview

Gene Mutations

• Gene mutations are changes to the structure of genes at the molecular level
• They are achieved by changing the nucleotide base sequence in the DNA
• There are three main types:
  • Substitution mutations: occur when one nucleotide is replaced by another
  • Insertion mutations: occur when one or more nucleotides are added to a DNA sequence
  • Deletion mutations: occur when one or more nucleotides are removed from a DNA sequence

Consequences of Base Substitutions

• Base substitution mutations can result in neutral, harmful or beneficial consequences
• Neutral mutations have no effect and are often found in non-coding DNA sequences
• Same-sense mutations are also considered silent mutations. They change a codon but not the amino acid. This is possible due to the degeneracy of the genetic code
• Harmful mutations dramatically change the protein structure, disrupting its biological activity.
  • Nonsense mutations change a codon for an amino acid into a stop codon, prematurely terminating translation. The resulting protein is unlikely to function.
  • Missense mutations change the codon for one amino acid into another, which can be either beneficial or harmful. Many genetic diseases are due to missense mutations but few are beneficial.
• Single-nucleotide polymorphisms (SNPs) are variations caused by single nucleotide substitutions and are inherited.

Consequences of Insertions and Deletions

• Insertions and deletions can have significant impacts on the function of proteins
• Insertions and deletions that occur in multiples of 3 nucleotides will result in extra or fewer codons in the mRNA. This leads to extra or fewer amino acids in the polypeptide.
• Frameshift mutations occur when the insertion or deletion is not a multiple of 3. This shifts the reading frame of codons, leading to potentially significant changes to the amino acid sequence.
  • The consequence of frameshift mutations is a change in the amino acid sequence and a potential disruption of the protein's function.
• Large insertions or deletions can disrupt the entire protein structure.
• Insertions and deletions can be harmful and lead to significant changes in the structure and function of proteins.

Mutation as a Source of Genetic Variation

• Mutations are a source of new alleles and therefore new genetic variation
• Mutations play a role in evolution because natural selection acts on these variations
• Mutations can also be beneficial, leading to adaptations that help organisms survive in different environments.