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iGenetics 3rd Edition by Peter Russell
Edition 3ISBN: 978-0321569769iGenetics 3rd Edition by Peter Russell
Edition 3ISBN: 978-0321569769 Exercise 2
In the 1920s, while working with Streptococcus pneumoniae (the agent that causes pneumonia), Griffith injected mice with different types of bacteria. For each of the following bacteria types injected, indicate whether the mice lived or died:
a. type IIR
b. type IIIS
c. heat-killed IIIS
d. type IIR + heat-killed IIIS
a. type IIR
b. type IIIS
c. heat-killed IIIS
d. type IIR + heat-killed IIIS
Explanation
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Verified
In 1928, a British medical officer by the name of Frederick Griffith conducted an experiment using live and dead bacteria. He used two strains of Streptococcus pneumonia , the R strain and the S strain. The R strain is rough and nonvirulent, while the S strain is smooth and virulent. In order to further facilitate his experiment, Griffith used two different types of the bacteria, those with type II coats and those with type III coats.
Thus, Griffith used Type IIR and Type IIIS bacteria. Since bacteria can mutate, it is possible for R bacteria to mutate into S and vice versa; however, there is not mutation between types. Type IIR bacteria can mutate into Type IIS bacteria but not into any Type III bacteria. Similarly, Type IIIR bacteria can mutate into type IIIS bacteria but not into any type II bacteria.
a) When Griffith injected Type IIR bacteria in to the mice, the mice survived with no bacteria present in their bloodstream. The mice survived because they were infected with the nonvirulent strain and there was no way for it to become virulent.
b) When Griffith injected Type IIIS bacteria in to mice, the mice died with virulent bacteria found in their bloodstream. The mice died because they were infected with the live virulent strain.
c) When Griffith injected heat-killed Type IIIS bacteria in to mice, the mice survived with no bacteria present in their bloodstream. The mice survived because they were infected with a dead strain, so it didn't matter if it was previously virulent or not.
d) Finally, when Griffith injected Type IIR bacteria and heat killed Type IIIS bacteria into mice, the mice died with Type IIIS bacteria found in their bloodstream. The mice died because the nonvirulent strain was transformed into the virulent strain through its interaction with the dead virulent strain.
Thus, Griffith used Type IIR and Type IIIS bacteria. Since bacteria can mutate, it is possible for R bacteria to mutate into S and vice versa; however, there is not mutation between types. Type IIR bacteria can mutate into Type IIS bacteria but not into any Type III bacteria. Similarly, Type IIIR bacteria can mutate into type IIIS bacteria but not into any type II bacteria.
a) When Griffith injected Type IIR bacteria in to the mice, the mice survived with no bacteria present in their bloodstream. The mice survived because they were infected with the nonvirulent strain and there was no way for it to become virulent.
b) When Griffith injected Type IIIS bacteria in to mice, the mice died with virulent bacteria found in their bloodstream. The mice died because they were infected with the live virulent strain.
c) When Griffith injected heat-killed Type IIIS bacteria in to mice, the mice survived with no bacteria present in their bloodstream. The mice survived because they were infected with a dead strain, so it didn't matter if it was previously virulent or not.
d) Finally, when Griffith injected Type IIR bacteria and heat killed Type IIIS bacteria into mice, the mice died with Type IIIS bacteria found in their bloodstream. The mice died because the nonvirulent strain was transformed into the virulent strain through its interaction with the dead virulent strain.
iGenetics 3rd Edition by Peter Russell
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