Edexcel IGCSE Biology: Double Science 复习笔记 3.2.6 Mutation

• Mutations are rare, random changes that occur in the sequence of DNA bases in a gene or a chromosome
• Mutations occur continuously
• As the DNA base sequence determines the sequence of amino acids that make up a protein, mutations in a gene can sometimes lead to a change in the protein that the gene codes for
• Most mutations do not alter the protein or only alter it slightly so that its appearance or function is not changed
• There are different ways that a mutation in the DNA base sequence can occur

Insertions

• A new base is randomly inserted into the DNA sequence
• An insertion mutation changes the amino acid that would have been coded for by the group of three bases in which the mutation occurs
  • Remember – every group of three bases in a DNA sequence codes for an amino acid

   

• An insertion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence

An example of an insertion mutation

Deletions

• A base is randomly deleted from the DNA sequence
• Like an insertion mutation, a deletion mutation changes the amino acid that would have been coded for by the group of three bases in which the mutation occurs
• Like an insertion mutation, a deletion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence

Substitutions

• A base in the DNA sequence is randomly swapped for a different base
• Unlike an insertion or deletion mutation, a substitution mutation will only change the amino acid for the group of three bases in which the mutation occurs; it will not have a knock-on effect

An example of a substitution mutation