Question

A DNA segment has base order AGC TTA TCG. Which copy exhibits a frameshift mutation through deletion?

a. TTA TCG
b. AGC TTA TAG
c. AGC TTT CG
d. AGC TCG

Answer 1

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.