please explain how you got the answer 4. Performing a complementation test throu
ID: 280800 • Letter: P
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please explain how you got the answer
4. Performing a complementation test through cotransduction using mutant phage genomes created by X-ray mutagenesis (mutants a-e), as well as ones created by chemical mutagenesis using EMS (mutants 1-5), you get the following results: 2 3 4 5 d+ Explain this data if mutants a-e are deletion mutants and 1-5 are point mutants. Analysis of the data can provide with a comparative map of the mutants. Create this map. + stands for observing mutation and for not observing it.Explanation / Answer
Both X-rays and EMS is involved in substitution type mutagenesis. X-rays mutate by DNA fragmentation or by thiamine dimer formation, in this state thiamine pairs with guanine instead of adenine (A), in subsequent replication thiamine (T) is replaced by cytosine. EMS does alkylation of guanine (G) results in wrong pairing with Thiamine instead of cytosine, in the subsequent replication G is replaced ultimately by adenine (A).
X-rays – T replaced with C
EMS - G replaced with A
Consider a-e deletion mutants
Consider 1-5 point mutants
Now we will deal our mutants.
EMS->
X-ray
?
1
2
3
4
5
a
-
+
+
-
-
b
-
+
-
-
-
c
+
+
-
-
+
d
+
-
+
+
-
e
-
-
+
+
-
The key principle here is that point mutations (1-5) can recombine with deletions (a-e) that do not extend past the mutation, but they cannot recombine to yield wild type (consider here – as no mutation observed or wild type) with deletions that do extend past the mutation. From the table and data given in the question, any mutation that recombines with deletion ‘a’ must be located before the deletion, any mutation that recombines with deletion ‘b’ must be located before the deletion ’b’, and so forth.
Look at point mutation 1 it recombines with c, d but not with a,b,e. Hence point mutation 1 should be before the c,d and not before a,b,e and this point mutations can be kept between c, d,e
Look at point mutation 2 it recombines with a,b,c but not with d,e. Hence point mutation 2 should be before the a,b,c and not before d,e and this point mutations can be kept between c,d
Look at point mutation 3 it recombines with a, d,e but not with b,c. Hence point mutation 3 should be before the a,b and d,c not before a,d,e and this point mutations can be kept before ab, dc
Look at point mutation 4 it recombines with d,e but not with a,b,c. Hence point mutation 4 should be before the d,e and not before a,b,c and this point mutations can be kept between dc
Look at point mutation 5 it recombines with ’c’ but not with a,b,d,e. Hence point mutation 5 should be before ‘c’ and not before a,b,d,e and this point mutations can be kept before cb, cd
The above things diagrammatically represented as
a -- 5-- -- -- --
b -- --1 -- -- --
c -- -- --4-- --
d -- -- -- -- --2
e -- -- -- --3--
EMS->
X-ray
?
1
2
3
4
5
a
-
+
+
-
-
b
-
+
-
-
-
c
+
+
-
-
+
d
+
-
+
+
-
e
-
-
+
+
-
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