1. Genetics NewsGenetics News

2. Mutation - Overview Mechanism of mutation Spontaneous Induced Duplication/Insertions Mechanism (example: lacI) Fragile X syndrome Repair of mutation Bypass replication Excision repair Mismatch repair

3. Mutation and its Avoidance Thrust DNA damage Base substitution Base mimicry Intercalation Parry Reversal of lesion Bypass of lesion General excision pathway Specific excision pathway Mismatch repair pathway

4. UV Pyrimidine dimers T-T C-T T-C Routes to Mutation DNA Damage

5. Light Repair Strategy #1 Reversal of mutation DNA photolyase

6. DNA Polymerase III Faithful Error-correcting SOS response Induced by DNA damage Elicits repair enzymes Recruits DNA Pol I Repair Strategy #2 Bypass of mutation

7. Modified DNA Polymerase III Resourceful Innovative Repair Strategy #2 Bypass of mutation SOS-induced genes

8. Modified DNA Polymerase III Resourceful Innovative 5'-AGATTGACCTAGAT 3'-CCTAACTGGATCTATTGTAA 5'-AGATTGACCTAGATAACATT 3'-CCTAACTGGATCTATTGTAA 5'-AGATTGACCTAGAT 3'-CCTAACTGGATCTATCGTAA 5'-AGATTGACCTAGATAACATT 3'-CCTAACTGGATCTATCGTAA Repair Strategy #2 Bypass of mutation When in doubt, A

9. Study Question 9 Bypass replication across pyrimidine dimers generally produces which kind of base substitution: Transitions? Transversions?

10. Transitions vs Transversions Transition: G A A C C T Transversion: G T T G C C C C A C C G Purine Purine; Pyrimidine Pyrimidine Purine Pyrimidine; Pyrimidine Purine

11. Study Question 9 Bypass replication across pyrimidine dimers generally produces which kind of base substitution: Transitions? Transversions?

12. Study Question 10 DNA Pol I mutant is viable. Mutation rate is lower in mutant. If viable and lower mutation rate, why have Pol I???

13. Routes to Mutation G A G T C G A G T C T C A G C T C A HNO 2 U Base modification Exposure to chemical mutagen Reaction with base to change base pairing Replication of modified base

14. Routes to Mutation G A G T C G A G T U Base modification Exposure to chemical mutagen Reaction with base to change base pairing C T C A G C T C A Replication of modified base GAGTCGAGT CTCAACTCA Mutation is permanent

15. Routes to Mutation G A G T C G A G T Base mimicry Incorporation of base mimic Replication of modified base CTCAGC Br UCA

16. Routes to Mutation G A G T C G A G T Base mimicry Incorporation of base mimic Replication of modified base Mutation is permanent G A G T C G G G T CTCAGC Br UCA C T C A G C T C A Change of pairing properties (tautomerization)

17. Problem: Deamination of cytosine What’s the threat?C/G to T/A transition Could you diagnose the problem?

18. Strategy #3: Repair Lesion Specific Excision Repair Excision of base by specific glycosylase Excision of strand by AP endonuclease AP Apurinic Apyrimidinic

19. Study Question 11 Two mutations: 1. Ura-glycosylase 2. AP endonuclease Combine both into one strain. Phenotype? Phenotype of Ura-glycossylase - mutant? Phenotype of AP endonuclease - mutant? Phenotype of double mutant?

20. Problem: Error in Replication 5'-AGATTGACCTAGAT T ATTGTTACTGACCGCATATC-3’ 3'-TCTAACTGGATCTAG TAACAATGACTGGCGTATAG-5’ Is it too late? Could you diagnose the problem?

21. Problem: Error in Replication Is it too late? Could you diagnose the problem? 5'-AGATTGACCTAGAT T ATTGTTACTGACCGCATATC-3’ 3'-TCTAACTGGATCTA G TAACAATGACTGGCGTATAG-5’

22. Strategy #2: Repair of Lesion Methyl-directed Mismatch Repair Old DNA strand Marked by methylation Methylation at adenine of GATC New DNA strand Unmarked Replication with standard nucleotides Mark is temporary Now can you diagnose the lesion?

23. Strategy #2: Repair of Lesion Methyl-directed Mismatch Repair MutS, H, L: protein Ssb: Single-stranded binding protein

24. Study Question 12 Phenotype of E. coli that can’t methylate GATC? Study Question 13 Phenotype of E. coli that overmethylates GATC?

25. Mutagenesis Slipped-strand mispairing Wild-type lacI Replication Mispairing Completion of replication 2 nd round of replication

26. Study Question 4 Draw a diagram showing how mispairing could lead to deletion of a repeat.

27. Fragile X Syndrome SQ5: Is the trait dominant? Recessive? SQ6: Why do females have two numbers?