Mutants that are detectable Non-motile Non-capsulated Rough colony Nutritional Sugar fermentation Drug resistant Ⅴ irus resistant Temperature sensitive gmentiess Cold sensitive
Mutants that are detectable • Non-motile • Non-capsulated • Rough colony • Nutritional • Sugar fermentation • Drug resistant • Virus resistant • Temperature sensitive • Pigmentless • Cold sensitive
5·TAc… Molecular ATG…5 MUTATION Normal ba f asis o Mutation A c T A C T G A T A T G · Point mutation ↓↓↓↓ Transcription Missense mutation A C U A G U AU U A C Nonsense mutation Asparagine 天so op Tyrosine Tyrosine codon 冬酰胺 codon 酪氨酸 Silent mutation Translation Faulty Incomplete Normal Normal Protein Protein Protein Protein Missense Nonsense Silent Wild type mutation mutation FIGURE 7.3 Possible effects of base pair substitution in a gene cod ing for a protein: three different protein products from changes in the DNA for a single codon
Molecular basis of Mutation • Point Mutation – Missense mutation – Nonsense mutation – Silent mutation 天冬酰胺 酪氨酸
Frameshift mutations GIC C G AT Insertion mutation TA CGG ACIC AA T AC T Altered reading frame 个m Normal DNA T GC CITIG T TA TG T A CG GAC A AT AC Normal reading frame Deletion Deletion mutation T GIC C GIT T AIT Fi T A CIG G CIA A TA Altered reading frame by Occur in protein-encoding gene that including the reading frame If occurs in promoter region, it is not frameshift
Frameshift mutations • Occur in protein-encoding gene that including the reading frame • If occurs in promoter region, it is not frameshift
Back mutations or reversions Point mutations are reversible Revertant wild type phenotype that was lost in the mutant is restored Same site revertants True revertants Second site mutation Suppressor mutation: restore the wild type phenotype by mutation somewhere else
Back Mutations or Reversions • Point Mutations are reversible • Revertant – wild type phenotype that was lost in the mutant is restored. • Same site revertants • True revertants • Second site mutation – Suppressor mutation: restore the wild type phenotype by mutation somewhere else
Mutations involving many base pairs Deletions: mutations in which a region of the dna has been eliminated Insertions occur when new bases are added to the dNA, can be a sing de base or many bases(called insertion sequences) Translocation: large section of chromosomal dna is moved to a new location
Mutations involving many base pairs • Deletions: mutations in which a region of the DNA has been eliminated • Insertions: occur when new bases are added to the DNA, can be a single base or many bases (called insertion sequences) • Translocation: large section of chromosomal DNA is moved to a new location