Assume you are mapping the location of a mutation using transduction. You have a
ID: 277596 • Letter: A
Question
Assume you are mapping the location of a mutation using transduction. You have a donor strain that is Wild-type for both the gene encoding Leucine and the gene encoding Tryptophan. You have a recipient strain that already has a mutation in the gene encoding Leucine and you add many random mutations. You expect that at least some of the mutations will be in the gene encoding Tryptophan. Given the data below, which strain has a Tryptophan mutation closest to the Leucine gene?
# of colonies when grown on Complete media
# of colonies when grown on media –leu, -trp
Before mixing with parent
1000
0
Strain A
1000
100
Strain B
1000
250
Strain C
1000
25
Strain D
1000
700
Strain A
Strain B
Strain C
Strain D
# of colonies when grown on Complete media
# of colonies when grown on media –leu, -trp
Before mixing with parent
1000
0
Strain A
1000
100
Strain B
1000
250
Strain C
1000
25
Strain D
1000
700
Explanation / Answer
Answer: Option D is correct.
Explanation:
Mapping by transduction:
If two genes are far away, the probability that they are cotransduced is very low.
If two genes are close by, the probability that they are cotransduced is very high.
In the given case, Leu-trp- stain can grow in the media lacking Leu and Trp only when it acquires both genes by transduction.
The number of colonies would be greater if both genes are close together so that their cotransduction frequency is high.
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