1. Two independent E. colimutants (1 and 2) are induced using mutagen X. After b
ID: 191270 • Letter: 1
Question
1. Two independent E. colimutants (1 and 2) are induced using mutagen X. After being mutated with mutagen X, each mutant is taken and exposed to the following mutagens: Bromouracil (BU), Nitrous Acid (NA), Hydroyl amine (HA) and Proflavin. The Table below shows the reversion frequency of each mutagen. Assume all the revertants are true revertants. (4 marks)
Mutant
No mutagen
BU
NA
HA
Proflavin
1
1.5 x10-8
5 x 10-5
1.3 x 10-4
1.6 x10-8
1.6 x 10-7
2
2 x10-7
2 x 10-4
6 x 10-5
3 x10-5
1.7 x 10-7
a. Make the best prediction possible about which base changes occurred in forming the original mutations (4 marks).
Mutation Probable base change
1
2
b. What kind of mutations are caused by mutagen X and why did you come to this conclusion? (3 marks)
2. You identify a third E. colimutation (3) using mutagen X. You decide to map 3 and find it is close to both the GAL and BIO genes. The normal distance between the wild type GAL and BIO genes is 20 map units. You cross 3 with a gal mutant (Cross1) and with a bio mutant(Cross 2) independently and get the following results:
You identify a third E. colimutation (3) using mutagen X. You decide to map 3 and find it is close to both the GAL and BIO genes. The normal distance between the wild type GAL and BIO genes is 20 map units. You cross 3 with a gal mutant (Cross1) and with a bio mutant(Cross 2) independently and get the following results:
Cross 1 Cross 2
GAL 3 145 BIO 3 105
gal + 120 bio + 80
GAL + 4 BIO + 6
gal 3 5 bio 3 8
+ = wild-type allele; 3 = mutant allele
a. Based on the above data what is the map distance between Gene 3 and GAL gene (Show work)? (2 marks)
b. What is the map distance between Gene 3 to the BIO gene (Show work)? (2 marks)
c. What does these results suggest about the molecular basis of mutation 3 and why do you come to this conclusion? (2 marks)
d. How would you expect mutation 3 to behave in a reversion test and why do you come to this conclusion? (2 marks)
Mutant
No mutagen
BU
NA
HA
Proflavin
1
1.5 x10-8
5 x 10-5
1.3 x 10-4
1.6 x10-8
1.6 x 10-7
2
2 x10-7
2 x 10-4
6 x 10-5
3 x10-5
1.7 x 10-7
Explanation / Answer
1a) In both mutants nitrous acid gives most high number revertants.Nitrous acid directly damage DNA by deamination of DNA bases adenine and or cytosine. So in mutation 1 & 2 adenine and/or cytosine ay be aminated.
b)the mutation caused by x may be amination of adenine or/and cytosine. because the deamination of nitrous acid gives true revertant that is removed the amine group added by the mutant.
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