7.5 Genetic Mutations

Point mutations - change in individual base pair, or small groups * Substitution * Insertion / Deletion * Inversion
Effects: amplified by # of codons affected * Missense * change in amino acid sequence * Nonsense * results in premature stop codon * polypeptide is shorter * Silent * no change in amino acid sequence * Frameshift * reading frame is changed resulting in different amino acid sequence from point of mutation

Multiple nucleotides, entire genes, or multiple genes
Types or large-scale mutations * Amplification / Gene Duplication: additional copies of genes * Deletion: loss of entire genes * deletion of dystrophin gene results in Duchenne muscular dystrophy * Translocation: movement of entire genes to another region of same or other chromosome * may disrupt gene at point of insertion or result in a new polypeptide * Inversion: region in a gene reverses direction

Spontaneous * caused by error in replication
Induced * caused by a mutagen (an environmental agent that can alter DNA sequence) * Chemical mutagens: * some mutagens modify nucleotides to resemble others, this leads to inaccurate copying because incorrect base pairs are inserted * others cause mutation because they have similar structures to a nitrogenous base and are mistakenly inserted, disrupting DNA structure (ex: ethidium bromide) * Radiation: * low energy radiation can affect the structure of the DNA molecule leading to complication in replication and transcription * high energy radiation (ionizing radiation) can break bonds and cause large-scale mutations