1. genotype
2. phenotype

1. genetic characteristic of organism
2. physical characteristic of organism

1. mutation
2. gene transfer
3. regulation of gene expression

1. base substitutions
2. removal or addition of nucleotides
3. transposable elements

1. point mutations - occur when one base pair is changed
2. missense mutations - resulting from amino acid substitution
3. nonsense mutations - changes an amino acid codon to a stop codon

base substitutions are the most common type of mutation

• shifts the codons (frameshift mutation)
• affects all amino acids downstream from addition or deletion
• frequently result in premature stop codons

• segments of SNA that move spontaneously from gene to gene
• elements are called transposons
• disrupts proper function of gene

1. chemical mutagens
2. transposition
3. radiation

• common procedure used to induce mutation in lab
• genes that receive transposon will undergo a knockout mutation (early start or stop codon)
• termed insertion mutation

1. UV light - causes covalent bonding between adjacent thymine bases; forms thymine dimers which distorts DNA
2. X-rays - cause breaks and alterations in DNA; breaks that occur on both strands are lethal

1. Proofreading - DNA polymerase replaces incorrect base with correct one
   
2. Mismatch repair - endonuclease removes short stretch of nucleotide, DNA polymerase fills gap, DNA ligase joins ends

1. Light repair - photoreactivation; enzyme uses visible light to break covalent bonds b/w bases
2. Dark repair - excision repair; endonuclease excises damaged section, new section replicated and joined to original strand

• SOS repair  - produces new DNA polyemerase; highly error prone; mutations can arise from synthesis with new enzyme

2 Mutation selection techniques

1. Direct selection  - inoculating population of bacteria on medium on which only mutants will grow (used to select antimicrobial resistant organisms)
2. Indirect selection  - required to isolate organisms that require growth factor that parent strain does not