Genetic Mutations

Definition of a mutation

A change in the sequence of base pairs in a DNA molecule

• results in an altered polypeptide that gene codes for

• tertiary structure protein will form new bonds in different places

Mutagenic Agents

• Environmental factors that increase the risk of mutations

• e.g. Higher energy and Ionising radiation/ Carcinogens

Insertion Mutation

• An extra base is added to the sequence

• a frameshift occurs to the right - all the subsequent codons are altered

• leads to formation of a different sequence of amino acids

Deletion Mutation

• A base is deleted from the sequence

• Frameshift occurs but to the left (subsequent bases move to the left)

Substitution Mutation

A base has changed for a different base

• No frameshift occurs - same number of bases remain

• Genetic code is degenerate (multiple codons that code for same amino acid)

Explain the three forms that substitution mutations can taken

1. Silent Mutation

   • change in the nucleotide sequence that results in the same amino acid sequence

2. Missense Mutation

   • alteration of a single amino acid in polypeptide chain

3. Nonsense Mutation

   • formation of a premature stop codon - polypeptide chain produced is incomplete

Inversion Mutation

• Section of bases detach from DNA base sequence

• When reattached the DNA base sequence is inverted (joins back to front)

Translocation Mutations

• section of bases of one chromosome detaches and attaches to another chromosome

• impacts gene expression and phenotype

• THIS IS NOT CROSSING OVER IN MEIOSIS