Question

Several auxotrophic point mutants in Neurospora are treated with various agents to see if reversion will take place. The following results were obtained (a plus sign indicates reversion; HA causes only G·C ? A·T transitions). Mutant 5-BU HA Proflavin Spontaneous reversion 1 – – – – 2 – – + + 3 + – – + 4 – – – + 5 + + – + a. For each of the five mutants, describe the nature of the original mutation event (not the reversion) at the molecular level. Be as specific as possible. b. For each of the five mutants, name a possible mutagen that could have caused the original mutation event. (Spontaneous mutation is not an acceptable answer.) c. In the reversion experiment for mutant 5, a particularly interesting prototrophic derivative is obtained. When this type is crossed with a standard wild-type strain, the progeny consist of 90 percent prototrophs and 10 percent auxotrophs. Give a full explanation for these results, including a precise reason for the frequencies observed.

          Several auxotrophic point mutants in Neurospora are treated with various agents to see if reversion will take place. The following results were obtained (a plus sign indicates reversion; HA causes only G·C ? A·T transitions).

Mutant 5-BU HA Proflavin Spontaneous reversion
1 – – – –
2 – – + +
3 + – – +
4 – – – +
5 + + – +

a. For each of the five mutants, describe the nature of the original mutation event (not the reversion) at the molecular level. Be as specific as possible.
b. For each of the five mutants, name a possible mutagen that could have caused the original mutation event. (Spontaneous mutation is not an acceptable answer.)
c. In the reversion experiment for mutant 5, a particularly interesting prototrophic derivative is obtained. When this type is crossed with a standard wild-type strain, the progeny consist of 90 percent prototrophs and 10 percent auxotrophs. Give a full explanation for these results, including a precise reason for the frequencies observed.

Several auxotrophic point mutants in Neurospora are treated with various agents to see if reversion will take place. The following results were obtained (a plus sign indicates reversion; HA causes only G·C ? A·T transitions).

Mutant 5-BU HA Proflavin Spontaneous reversion
1 – – – –
2 – – + +
3 + – – +
4 – – – +
5 + + – +

a. For each of the five mutants, describe the nature of the original mutation event (not the reversion) at the molecular level. Be as specific as possible.
b. For each of the five mutants, name a possible mutagen that could have caused the original mutation event. (Spontaneous mutation is not an acceptable answer.)
c. In the reversion experiment for mutant 5, a particularly interesting prototrophic derivative is obtained. When this type is crossed with a standard wild-type strain, the progeny consist of 90 percent prototrophs and 10 percent auxotrophs. Give a full explanation for these results, including a precise reason for the frequencies observed.

Added by Emma T.

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