This document presents information on gene stability, DNA repair, and mutation. It discusses sources of mutation like errors in DNA replication and damage from mutagens like chemicals and radiation. It then describes the different DNA repair systems, including photoreactivation/direct repair, excision repair, mismatch repair, and SOS repair. The conclusion is that a possible definition of mutation is a deficiency in DNA repair.

1. Gene stability and DNA repair…Presented by Minakshisaikia2nd semester, 23rdFebruary 20101

2. “Mutation”2

3. Mutation…Error in DNA replication.Damaging effects of mutagens(chemicals and radiations).CHEMICALS: Alkylating agents like nitrosoguanidine, nitrosamine, etc.RADIATIONS: X-rays, U.V.rays, etc.3

4. 1.ERROR IN REPLICATION…4

5. 2.ONE POSSIBLE EFFECT OF MUTAGEN5

6. “DNA repair system”6

7. 7

8. DNA repair in a nut shell…8

9. 1.PHOTOREACTIVATION /direct repair system…As the name suggests it acts directly on damaged nucleotides, converting each one back to its original structure.9

10. Thymine dimerisation…10

11. 2.EXCISION REPAIR SYSTEM…It involves excision of a segment of the polynucleotide containing a damaged site, followed by resynthesis of the correct nucleotide sequence by a DNA Polymerase.11

12. ‘Excision repair system’12

13. 3.MISMATCH REPAIR SYSTEM… It corrects errors of replication, again by excising a stretch of single-stranded DNA containing the offending nucleotide and then repairing the resulting gap.13

14. Methylation process…14

15. ‘mismatch repair system’15

16. 4.SOS REPAIR SYSTEM…‘Save Our Souls’The SOS repair system is an emergency measure for copying with a damaged genome.This is error prone.16

17. ‘SOS repair system’17

18. Conclusion:“A possible definition of mutation is therefore a deficiency in DNA repair…”18

19. Bibliography…Genomes 3, T.A.BrownGenes vii, Benjamin LewinInternet, Google Search19

20. Thankyou… for your patience!!!20