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Higher Biology
Chapter 16
Gene Mutations
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.
• 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.
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.
Substitution
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.
Inversion of Two or More
Nucleotides
“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)
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.
Deletion of a Nucleotide
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.
Insertion of a Nucleotide
‘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 gene’s DNA to be misread.
• The proteins produced differ from the normal
proteins by many amino acids and tend to be nonfunctional.
• If these proteins are enzymes which catalyse
essential steps in the metabolic pathway, the
pathway will become disrupted. (PKU)
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.