A frameshift mutation occurs when nucleotides are added or deleted from the DNA sequence in a number that is not a multiple of three, which causes the reading frame of the genetic code to shift.
The original DNA segment is: AGC TTA TCG
Let's analyze the provided options for deletions:
- AGC TCG - This sequence appears to be missing one nucleotide (the second "T" from "TTA"). This deletion causes a frameshift since it changes the reading frame for subsequent codons.
- AGC TTA TAG - This sequence has not undergone a frameshift mutation through deletion; it simply replaces "TCG" with "TAG," which is a substitution.
- TTA TCG - This sequence is missing the first "AGC," which also results in a frameshift, but it is a deletion of three bases. This could potentially restore the reading frame if it were in multiples of three.
- AGC TTT CG - This sequence has undergone a change by substituting the second "A" with "T" and deleting one "CG," which can result in a frameshift, but it can be considered a substitution and a deletion simultaneously.
Given these options, the one that clearly shows a frameshift mutation through deletion is AGC TCG.