Microbial Genetics - Mutation l Mutation - Introduction –A mutation is a change in the DNA sequence that results in a change in the product protein –Mutations can be neutral, harmful (most) or beneficial –Mutation is the basis of variation within a species and thus provides an important mechanism to evolution

Microbial Genetics - Mutation l Types of Mutation –Base-pair substitution - misssense change in amino acid sequence –Base-pair substitution - nonsense change in DNA sequence - premature stop –Frameshift »Insertion »Deletion

Microbial Genetics - Mutation l Normal gene –DNA transcribed –mRNA translated –No change in gene product

Microbial Genetics - Mutation l Missense mutation –Base substitution –Changes amino acid sequence by one amino acid –May or may not affect activity of protein

Microbial Genetics - Mutation l Nonsense mutation –Mutation changes codon to stop codon –Premature termination of protein –Almost always destroys activity of protein

Microbial Genetics - Mutation l Frameshift mutation –inserts or deletes a base in the DNA –Protein may be of correct size (approximately) –Protein sequence altered significantly

Microbial Genetics - Mutation l Mutatgens –Chemicals that modify DNA »Deaminating agents »Methylating agents »Intercalating agents –Radiation »UV - UV repair system »X-Rays

Effect of UV Light Production of Thymine Dimers Repair of Tymine Dimers

Microbial Genetics - Mutation l Frequency –Rate at which change occurs usually low –Mostly random although there are “hot spots” –Low rate necessary to provide genetic diversity –Rate can change depending upon what population of cells is exposed to