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GENE MUTATIONS aka point mutations Gene mutations which affect only one gene DNA sequence ↓ Transcription mRNA sequence ↓ Translation Polypeptide © 2010 Paul Billiet ODWS 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 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 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 Substitution mutation GGTCTCCTCACGCCA GGTCTTCTCACGCCA ↓ ↓ CCAGAGGAGUGCGGU CCAGAAGAGUGCGGU Codons ↓ ↓ Pro-Glu-Glu-Cys-Gly Pro-Glu-Glu-Cys-Gly Amino acids © 2010 Paul Billiet ODWS Disaster Normal gene GGTCTCCTCACGCCA ↓ CCAGAGGAGUGCGGU Codons ↓ Pro-Glu-Glu-Cys-Gly Amino acids © 2010 Paul Billiet ODWS 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 © 2010 Paul Billiet ODWS 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 © 2010 Paul Billiet ODWS Addition mutation GGTGCTCCTCACGCCA ↓ CCACGAGGAGUGCGGU ↓ Pro-Arg-Gly-Val-Arg Mutations: Deletions A frame shift mutation Normal gene GGTCTCCTCACGCCA ↓ CCAGAGGAGUGCGGU Codons ↓ Pro-Glu-Glu-Cys-Gly Amino acids © 2010 Paul Billiet ODWS Deletion mutation GGTC/CCTCACGCCA ↓ CCAGGGAGUGCGGU ↓ Pro-Gly-Ser-Ala-Val
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