To identify which sequence shows a substitution mutation, we need to compare the given DNA sequences to find a point where one nucleotide is replaced with another.
Let's review the options to see if any of them display this type of change compared to the original sequence:
- Original Sequence:
- Top Strand: C G T T A C T G C A A T
- Bottom Strand: G C A A T G A C G T T A
Now, let's examine the response options:
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First Option:
- Top Strand: C G T C T A C T G C A A T
- Bottom Strand: G C A G A T G A C G T T A
- Change: 1st nucleotide in top strand changed from T to C (substitution) and in bottom strand, 2nd nucleotide changed from A to G.
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Second Option:
- Top Strand: C G T A C T G C A A T
- Bottom Strand: G C A T G A C G T T A
- Change: Top strand has changed T to A and bottom strand changed A to T.
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Third Option:
- Top Strand: C G T T A C T G C A A T
- Bottom Strand: G C A A T G A C G T T A
- Change: No substitutions.
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Fourth Option:
- Top Strand: C G T G A C T G C A A T
- Bottom Strand: G C A C T G A C G T T A
- Change: The top strand changes T to G and bottom strand changes A to C, indicating a substitution.
Based on the comparisons, the sequences showing substitution mutations are:
- First Option: Shows substitutions T to C (top) and A to G (bottom).
- Second Option: Shows substitution T to A and A to T.
- Fourth Option: Shows substitution T to G (top) and A to C (bottom).
However, we need to pick one. Among the provided options, the first option shows a substitution mutation clearly by changing specific nucleotides in both strands.
So the answer is the first option.