Question

Question 3
A)
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)
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 A
b. C G T G A C T G C A A T
G C A C T G A C G T T A
c. C G T T A C T G C A A T
G C A A T G A C G T T A
d. C G T A C T G C A A T
G C A T G A C G T T A

Answer 1

A substitution mutation occurs when one base in the DNA sequence is replaced with another.

Let's analyze the options based on the given original DNA sequence:

Original 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
```

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 A
```
- The first row has a substitution at the second position (T changed to C) and at the last position (A changed to G).
- The second row has a substitution at the third position (A changed to G).

b.
```
C G T G A C T G C A A T
G C A C T G A C G T T A
```
- The first row has a substitution at the third position (T changed to G).
- The second row has a substitution at the second position (A changed to C).

c.
```
C G T T A C T G C A A T
G C A A T G A C G T T A
```
- This option is exactly the same as the original sequence, meaning no mutation has occurred.

d.
```
C G T A C T G C A A T
G C A T G A C G T T A
```
- The first row has a substitution at the third position (T changed to A).
- The second row has a substitution at the third position (A changed to T).

Based on this analysis, the sequences with substitution mutations are options **a**, **b**, and **d**.

If we are looking for just one option that shows a substitution mutation, any of these (a, b, or d) would qualify. However, since only one answer is needed, and based on the options listed:

**d.** C G T A C T G C A A T
G C A T G A C G T T A

This option clearly shows substitutions that can be easily observed in both rows.

Correct answer: **d.**