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Spontaneous Mutations quiz #1

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  • Which of the following mechanisms can result in a spontaneous mutation?
    Spontaneous mutations can result from errors in DNA replication, natural DNA damage (such as from UV light), and tautomeric shifts in DNA bases. These processes occur without external induction and can lead to genetic changes.
  • What did the fluctuation test by Luria and Delbrück demonstrate about the origin of bacterial resistance to bacteriophages?
    It showed that bacterial resistance to bacteriophages arises from spontaneous mutations, not from exposure to the phage itself.
  • How did the number of resistant colonies differ between small cultures exposed to phage and the large culture not exposed in the fluctuation test?
    The small cultures exposed to phage showed a wide range of resistant colonies (1 to 107), while the large culture not exposed had 14 to 26, indicating randomness unrelated to phage presence.
  • Why does the presence of a bacteriophage not consistently induce the same number of resistant colonies in bacterial cultures?
    Because resistance arises from spontaneous mutations, not from phage-induced changes, so the number of resistant colonies varies randomly.
  • What is a tautomeric shift and how can it lead to spontaneous mutations?
    A tautomeric shift is a change in the position of protons in DNA bases, creating alternative forms that can pair incorrectly and cause mutations.
  • How do tautomeric forms of DNA bases differ from the common forms discussed in genetics?
    Tautomeric forms have different proton positions, which can result in unusual base pairings not typically seen in standard DNA replication.
  • What genetic disease is associated with excessive trinucleotide repeats due to spontaneous mutation mechanisms?
    Fragile X Syndrome is associated with excessive CGG trinucleotide repeats caused by spontaneous mutation mechanisms.
  • What is strand slippage and how does it contribute to trinucleotide repeat disorders?
    Strand slippage occurs when repetitive DNA sequences loop out during replication, causing the polymerase to add extra repeats and leading to disorders like Fragile X Syndrome.
  • Why are trinucleotide repeat regions particularly susceptible to strand slippage during DNA replication?
    Because their repetitive sequences can easily bind to themselves and form loops, making it likely for the polymerase to duplicate sections.
  • What types of DNA damage, aside from replication errors, can lead to spontaneous mutations?
    Naturally occurring DNA damage such as depurination and deamination, often caused by environmental factors like UV light, can lead to spontaneous mutations.
  • Why do RNA viruses have higher rates of mutation compared to DNA-based organisms?
    RNA viruses have higher rates of mutation because their replication enzymes, such as RNA-dependent RNA polymerases, lack the proofreading ability found in DNA polymerases. This leads to more frequent errors during replication, resulting in a higher mutation rate.