Final answer:
A transition base substitution in a DNA sequence occurs when a purine is replaced with another purine, or a pyrimidine is replaced with another pyrimidine, so C to G and A to G are the correct examples of transition base substitutions.
Step-by-step explanation:
A transition base substitution within a DNA sequence occurs when a purine is replaced by another purine, or a pyrimidine is replaced by another pyrimidine. In DNA, adenine (A) and guanine (G) are purines, while cytosine (C) and thymine (T) are pyrimidines.
Therefore, a transition is a substitution like A to G or C to T.
The correct answers from the options provided are:
C to G (changing one purine to another)
A to G (changing one purine to another)
These two options represent transition base substitutions.
The other options (A to T and G to T) are transversions, which is a substitution of a purine to a pyrimidine or vice versa.
Question: Within a DNA sequence, which of the following represents a transition base substitution?
A to T
C to G
A to C
G to T