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
Choice 1
C G T A C T G C A A T
G C A T G A C G T T A
Choice 2
C G T T A C T G C A A T
G C A A T G A C G T T A
Choice 3
C G T G A C T G C A A T
G C A C T G A C G T T A
Choice 4
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
A substitution mutation occurs when a single nucleotide is replaced by another. Let's compare each choice to the original sequence to find the one with the substitution:
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
Choice 1 (potential mutation is underlined):
C G T A C T G C A A T
G C A T G A C G T T A
(There is a substitution at the fourth position where T is replaced by A in the first strand, and A is replaced by T in the second strand.)
Choice 2:
C G T T A C T G C A A T
G C A A T G A C G T T A
(There is no change; this sequence is the same as the original.)
Choice 3:
C G T G A C T G C A A T
G C A C T G A C G T T A
(There is a substitution at the fourth position where T is replaced by G in the first strand, and A is replaced by C in the second strand.)
Choice 4:
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
(There is a substitution at the fourth position where T is replaced by C in the first strand, and A is replaced by G in the second strand.)
Therefore, Choices 1, 3, and 4 show a substitution mutation, while Choice 2 does not.