A frameshift mutation occurs when there is a deletion or insertion of nucleotides in a DNA sequence that changes the reading frame of the sequence. For a deletion to be classified as a frameshift, it typically involves the removal of one or more bases that aren’t in multiples of three, leading to an altered reading frame.
The original DNA sequence you provided is: AGC TTA TCG.
Let's consider each option and determine if it exhibits a frameshift mutation due to deletion.
a. TTA TCG
- This segment is missing the first three bases (AGC). This deletion would cause a frameshift mutation since the sequence starts from a different base.
b. AGC TTA TAG
- This sequence has the last base changed to G (TAG instead of TCG). This does not result from deletion but rather a base substitution. It does not qualify as a frameshift mutation.
c. AGC TTT CG
- This sequence involves a substitution (the second T in TTA has changed to TTT and last base has been deleted). However, it’s ambiguous whether it qualifies as a complete frameshift since it maintains some overlap.
d. AGC TCG
- This sequence has deleted the middle base (T from TTA), which results in a frameshift since the reading frame is altered.
Based on this analysis, option d. AGC TCG exhibits a frameshift mutation through deletion.