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GENE MUTATIONS aka point mutations
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Gene mutations which affect only one gene
DNA sequence ↓ mRNA sequence Polypeptide Transcription Translation © 2010 Paul Billiet ODWS
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DNA (template strand) mRNA Polypeptide Normal gene GGTCTCCTCACGCCA ↓
CCAGAGGAGUGCGGU Codons Pro-Glu-Glu-Cys-Gly Amino acids The template strand is the DNA strand which mRNA uses for transcription. © 2010 Paul Billiet ODWS
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Mutations: Substitutions
Normal gene GGTCTCCTCACGCCA ↓ CCAGAGGAGUGCGGU Codons Pro-Glu-Glu-Cys-Gly Amino acids Substitution mutation GGTCACCTCACGCCA ↓ CCAGUGGAGUGCGGU Pro-Arg-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) © 2010 Paul Billiet ODWS
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No change A mutation may have no effect on the phenotype.
Changes in the third base of a codon often have no effect. Normal gene GGTCTCCTCACGCCA ↓ CCAGAGGAGUGCGGU Codons Pro-Glu-Glu-Cys-Gly Amino acids Substitution mutation GGTCTTCTCACGCCA ↓ CCAGAAGAGUGCGGU Pro-Glu-Glu-Cys-Gly © 2010 Paul Billiet ODWS
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Disaster Normal gene Substitution mutation GGTCTCCTCACGCCA
↓ CCAGAGGAGUGCGGU Codons Pro-Glu-Glu-Cys-Gly Amino acids Substitution mutation GGTCTCCTCACTCCA ↓ CCAGAAGAGUGAGGU Pro-Glu-Glu-STOP © 2010 Paul Billiet ODWS
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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 © 2010 Paul Billiet ODWS
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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 © 2010 Paul Billiet ODWS
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Mutations: Deletions A frame shift mutation Normal gene
GGTCTCCTCACGCCA ↓ CCAGAGGAGUGCGGU Codons Pro-Glu-Glu-Cys-Gly Amino acids Deletion mutation GGTC/CCTCACGCCA ↓ CCAGGGAGUGCGGU Pro-Gly-Ser-Ala-Val © 2010 Paul Billiet ODWS
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