Higher Biology

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Higher Biology

• Chapter 16
• Gene Mutations

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Gene Mutations

• This type of mutation involves a change in one or
  more of the nucleotides in a strand of DNA.
• There are four types of gene mutation
• 1. Substitution of a nucleotide.
• 2. Inversion of two or more nucleotides.
• 3. Deletion of a nucleotide.
• 4. Insertion of a nucleotide.

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• In all of these cases one or more codons for one
  or more particular amino acids have become
  altered.
• This in turn leads to a change in the protein
  which is synthesised.
• For a protein to work properly it must have the
  correct sequence of amino acids.

4
Gene Mutations

• This type of mutation involves a change in one or
  more of the nucleotides in a strand of DNA.
• There are four types of gene mutation
• 1. Substitution of a nucleotide.
• 2. Inversion of two or more nucleotides.
• 3. Deletion of a nucleotide.
• 4. Insertion of a nucleotide.

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Substitution
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Gene Mutations

• This type of mutation involves a change in one or
  more of the nucleotides in a strand of DNA.
• There are four types of gene mutation
• 1. Substitution of a nucleotide.
• 2. Inversion of two or more nucleotides.
• 3. Deletion of a nucleotide.
• 4. Insertion of a nucleotide.

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Inversion of Two or More Nucleotides
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Point Mutations

• Substitution and inversion are known as point
  mutations.
• These bring about minor changes as only one amino
  acid is affected.
• Sometimes the organism is affected slightly or
  not at all.
• However when the substituted amino acid occurs at
  a critical position in the protein then a major
  defect may arise. (Sickle cell anaemia)

9
Gene Mutations

• This type of mutation involves a change in one or
  more of the nucleotides in a strand of DNA.
• There are four types of gene mutation
• 1. Substitution of a nucleotide.
• 2. Inversion of two or more nucleotides.
• 3. Deletion of a nucleotide.
• 4. Insertion of a nucleotide.

10
Deletion of a Nucleotide
11
Gene Mutations

• This type of mutation involves a change in one or
  more of the nucleotides in a strand of DNA.
• There are four types of gene mutation
• 1. Substitution of a nucleotide.
• 2. Inversion of two or more nucleotides.
• 3. Deletion of a nucleotide.
• 4. Insertion of a nucleotide.

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Insertion of a Nucleotide
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Frameshift Mutations

• Insertion and deletion gene mutations are known
  as frameshift mutations.
• These mutations lead to major changes as they
  cause a large portion of the genes DNA to be
  misread.
• The proteins produced differ from the normal
  proteins by many amino acids and tend to be
  non-functional.
• If these proteins are enzymes which catalyse
  essential steps in the metabolic pathway, the
  pathway will become disrupted. (PKU)

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Gene Mutations

• Since most proteins are indispensible to the
  organism, most gene mutations produce an inferior
  version of the phenotype.
• If these changes result in death (eg. albino
  plants) then the altered gene is said to be
  lethal.