You have made a collection of mutant fruit flies that aredefective in various as

Question

You have made a collection of mutant fruit flies that aredefective in various aspects of DNA repair. You test each mutantfor its hypersensitivity to three DNA-damaging agents: sunlight,nitrous acid (which causes deamination of cytosine), and formicacid (which causes depurination). The results aresummarized in the figure below, where a“yes” indicates that the mutant is more sensitive thana normal fly and blanks indicate normal sensitivity.

Which of the mutants is most likely to be defective in theDNA repair polymerase? Explain

   ...........................Sunlight| nitrous acid|     formic acid |    

Dracula                | Yes    |                     |                       |

Faust                    |           |      Yes         |                      |

Mole                    |  Yes   |                     |                       |

Mr. Self-destruct |   Yes   |       Yes       |       Yes         |

Marguerite         |            |                     |        Yes         |

Explanation / Answer

      The three damagingsunlight, nitrous acid and formic acid cause different types ofdamage in the DNA.       Sunlight cause formationof pyrimidine dimers, nitrous acid causes deamination of cytosineand formic acid causes       depurination.       The damage that is causedby sunlight is repaired by DNA photolyases while DNA polymerase isinvolved in the repair       of the damage that iscaused by nitrous acid and formic acid.       Therefore, the mutantsthat are most likely to be defective in DNA repair polymeraseare Dracula and mole.       This is because, these twomutants are damaged by sunlight where DNA polymerase cannot repairthem while all other       mutant can be repaired byDNA polymerase.

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