Question

Look at the DNA sequence.

C G T T A C T G C A A T
G C A A T G A C G T T A
Which sequence shows a substitution mutation?

(1 point)
Responses which answer is correct and why

C G T G A C T G C A A T
G C A C T G A C G T T AC G T G A C T G C A A T G C A C T G A C G T T A

C G T A C T G C A A T
G C A T G A C G T T AC G T A C T G C A A T G C A T G A C G T T A

C G T T A C T G C A A T
G C A A T G A C G T T AC G T T A C T G C A A T G C A A T G A C G T T A

C G T C T A C T G C A A T
G C A G A T G A C G T T AC G T C T A C T G C A A T G C A G A T G A C G T T A
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Answer 1

To determine which sequence shows a substitution mutation compared to the original DNA sequence, we need to identify a position where a single nucleotide in the original sequence is replaced with a different nucleotide in one of the provided options.

The original sequence is:
```
C G T T A C T G C A A T
G C A A T G A C G T T A
```

Now, let's compare this sequence to each of the provided options for substitutions:

1. **First Option:**
```
C G T G A C T G C A A T
G C A C T G A C G T T A
```
- DNA mutations:
- First line: **T** changed to **G**.
- Second line: **A** changed to **C**.
- Both lines show substitutions. **This option contains substitution mutations.**

2. **Second Option:**
```
C G T A C T G C A A T
G C A T G A C G T T A
```
- DNA mutations:
- First line: **T** changed to **A**.
- Second line: **A** changed to **T**.
- Both lines show substitutions. **This option contains substitution mutations.**

3. **Third Option:**
```
C G T T A C T G C A A T
G C A A T G A C G T T A
```
- No mutations: The sequences are identical.
- **This option does not contain any mutations.**

4. **Fourth Option:**
```
C G T C T A C T G C A A T
G C A G A T G A C G T T A
```
- DNA mutations:
- First line: **T** changed to **C** (first line).
- Second line: **A** changed to **G** (second line).
- Both lines show substitutions. **This option contains substitution mutations.**

### Conclusion

All options except the third contain substitution mutations. However, if the question asks for just one correct answer showing a substitution mutation, any of the first, second, or fourth options would be correct.

If we must choose a singular answer and the order of preference matters, **the first option** shows substitutions at clear, simple and different positions, making it a very good example.

**Most Suitable Answer: The first option.**