GENE MUTATIONS
point mutations
Gene mutations affect only one gene
Transcription Translation
DNA sequence
↓
mRNA sequence
↓
Polypeptide
DNA (antisense strand)
...
GENE MUTATIONS
point mutations
Gene mutations affect only one gene
Transcription Translation
DNA sequence
↓
mRNA sequence
↓
Polypeptide
DNA (antisense strand)
mRNA
Polypeptide
Normal gene
GGTCTCCTCACGCCA
↓ CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
The antisense strand is the DNA strand which acts as the template for mRNA transcription
Mutations: Substitutions
Normal gene
GGTCTCCTCACGCCA
↓ CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
Substitution mutation
GGTCACCTCACGCCA
↓ CCAGUGGAGUGCGGU
↓
Pro-Val-Glu-Cys-Gly
Substitutions will only affect a single codon
Their effects may not be serious unless they affect an amino acid that is essential for the structure and function of the finished protein molecule (e.g. sickle cell anaemia)
© 2016 Paul Billiet ODWS
The genetic code is degenerate
A mutation may have no effect on the phenotype
Changes in the third base of a codon often have no effect.
No change
Normal gene
GGTCTCCTCACGCCA
↓ CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
Substitution mutation
GGTCTTCTCACGCCA
↓ CCAGAAGAGUGCGGU
↓
Pro-Glu-Glu-Cys-Gly
Disaster
Normal gene
GGTCTCCTCACGCCA
↓ CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
Substitution mutation
GGTCTCCTCACTCCA
↓ CCAGAAGAGUGAGGU
↓
Pro-Glu-Glu-STOP
Mutations: Inversion
Inversion mutations, also, only affect a small part of the gene
Normal gene
GGTCTCCTCACGCCA
↓ CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
Inversion mutation
GGTCCTCTCACGCCA
↓ CCAGGAGAGUGCGGU
↓
Pro-Gly-Glu-Cys-Gly
Mutations: Additions
A frame shift mutation
Normal gene
GGTCTCCTCACGCCA
↓ CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
Addition mutation
GGTGCTCCTCACGCCA
↓ CCACGAGGAGUGCGGU
↓
Pro-Arg-Gly-Val-Arg
Mutations: Deletions
.........................................................continued................................................................................
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