Released STAAR Biology EOC · 2026 · Item 25 · 1 point

Walkthrough: Biology 2026, Item 25

B.7C · Mutations · unscored study

A student is creating a table with an example of a DNA sequence that experienced a mutation and a description of this mutation. Which table provides the BEST example and description of a frameshift mutation?

Original DNA: 3’ CGT TAT GCT T 5’ Mutated DNA: 3’ CTC GTA TTG T 5’ Mutation description: A section of DNA breaks away and reattaches to the chromosome in the reverse order without affecting the resulting protein.
Original DNA: 3’ CGT TAT GCT T 5’ Mutated DNA: 3’ CGT GTA TGC TT 5’ Mutation description: A single base is inserted, which could result in a protein with a different amino acid sequence and shape.
Original DNA: 3’ CGT TAT GCT T 5’ Mutated DNA: 3’ CGT AAT GCT T 5’ Mutation description: One base is substituted for another, which could result in a stop codon and a protein with a different amino acid sequence and shape.
Original DNA: 3’ CGT TAT GCT T 5’ Mutated DNA: 3’ CGT TAA GCT T 5’ Mutation description: A single base is changed and codes for the same amino acid without affecting the resulting protein.

1. Understand the question

A frameshift mutation changes the reading frame. Look for one base added or removed, so every codon after it shifts.

Try the question on your own first, then reveal one step at a time.

2. Solve it step by step

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Question, artwork, answer key and rationale: Texas Education Agency released STAAR test. Walkthrough steps written by TEKSForge. Studying here does not change your mastery or scores.