Please explain why A is the answer, will give a thumbs up for a good explanation

Question

Please explain why A is the answer, will give a thumbs up for a good explanation.

19You sequence a region around a Nhel restriction site in a wild-type individual. The sequence is : 5 ' GCTAGCTG3' You then sequence the corresponding region in an individual with a single point mutation. The substitution mutation results in the elimination of the Nhel site but it simultaneously created a new Pvull restriction site. The recognition sites for the two enzymes are Nhel 5 ' GCTAGC 3 The sequence of this region in the mutant individual is A 5'GCCAGCTG3' B 5'GCTAGCTG3 C 5'GTCGATCG3 D None of the above E More information needed PvulI 5'CAGCTG3'

Explanation / Answer

Sequence for NheI site is 5' GCTAGCTG 3'. sequence for PvuII is 5'CAGCTG 3'. It is given in the question that there is a single point mutation, meaning change in only one of the bases compared to the sequence for NheI. Now, If a mutation occurs at third site , so that T of NheI is mutated to C, such that now the sequence becomes GCCAGCTG. (INSTEAD OF GCTAGCTG). in the mutated sequence, 5'GCCAGCTG3' we observe that it no longer serves as site for the NheI enzyme. But, the last six bases, i.e. CAGCTG of the mutated sequence corresponds to site of pvuII . HENCE CORRECT CHOICE IS (A) 5' GC CAGCTG 3'

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