Practice MCQs Optional & Subjects

CRISPR-Cas9 Gene Editing: How It Works and Its Limits — MCQs with Answers

Test what you know about CRISPR-Cas9 Gene Editing: How It Works and Its Limits with 10 UPSC Prelims-style questions. Try each one first, then tap “Show answer” for the correct option and its explanation.

Read the full article
  • 10 practice questions
  • ≈ 10 min
  • Answers & explanations

Answers revealed

Try each question yourself first, then check the answer.

  1. Q1. With reference to CRISPR-Cas9, consider the following statements: 1. The guide RNA helps direct Cas9 towards a DNA sequence complementary to it. 2. Cas9 is the enzyme that makes a DNA cut. Which of the statements given above is/are correct?

    1. Both 1 and 2
    2. 2 only
    3. 1 only
    4. Neither 1 nor 2
    Show answer

    Correct answer: (A) Both 1 and 2

    Explanation

    Correct Answer: (A). Both statements are correct. The guide RNA is designed to pair with the chosen DNA sequence and helps Cas9 locate it. Cas9 is the nuclease that cuts DNA. The guide contributes to targeting, while the protein carries out the cleavage step.

  2. Q2. In the common CRISPR-Cas9 arrangement, which component makes the DNA cut?

    1. Guide RNA
    2. Cas9 nuclease
    3. DNA repair template
    4. Cell membrane
    Show answer

    Correct answer: (B) Cas9 nuclease

    Explanation

    Correct Answer: (B). Cas9 is the nuclease in this arrangement and makes the DNA cut. The guide RNA helps direct Cas9 to a matching target, but it is not the cutting enzyme. A repair template, when supplied, can influence repair but does not cut DNA.

  3. Q3. Consider the following statements about DNA repair after a CRISPR-Cas9 cut: 1. Cellular repair can introduce small insertions or deletions. 2. A supplied DNA template may guide a planned change in some contexts. 3. Supplying a template guarantees the intended edit in every cell. How many of the above statements are correct?

    1. Only one
    2. All three
    3. Only two
    4. None
    Show answer

    Correct answer: (C) Only two

    Explanation

    Correct Answer: (C). Statements 1 and 2 are correct. Cellular repair can create small insertions or deletions, and a supplied template may guide a planned change. Statement 3 is incorrect because template-directed repair varies with cell type and context and does not guarantee the intended result in every cell.

  4. Q4. Consider the following pairs: 1. Guide RNA : helps target a DNA sequence 2. Cas9 : DNA-cutting nuclease 3. Cellular repair : shapes the resulting edit How many of the above pairs are correctly matched?

    1. Only one
    2. Only two
    3. None
    4. All three
    Show answer

    Correct answer: (D) All three

    Explanation

    Correct Answer: (D). All three pairs are correctly matched. The guide RNA helps identify the target sequence, Cas9 acts as the nuclease that cuts DNA, and cellular repair produces much of the final outcome. The system therefore combines targeting, cleavage and repair rather than one single editing action.

  5. Q5. Which statement best describes somatic genome editing?

    1. It affects treated non-reproductive cells
    2. It is always inherited by future generations
    3. It edits every cell in the body
    4. It requires editing an embryo
    Show answer

    Correct answer: (A) It affects treated non-reproductive cells

    Explanation

    Correct Answer: (A). Somatic editing acts on non-reproductive cells of the treated person. It is intended to affect that person, not to change the genetic material passed to children. It does not necessarily reach every cell, and somatic editing is distinct from germline editing.

  6. Q6. With reference to germline editing, consider the following statements: 1. It may affect an egg, sperm or embryo. 2. A resulting change may be inherited by future generations. Which of the statements given above is/are correct?

    1. 1 only
    2. Both 1 and 2
    3. 2 only
    4. Neither 1 nor 2
    Show answer

    Correct answer: (B) Both 1 and 2

    Explanation

    Correct Answer: (B). Both statements are correct. Germline editing may involve an egg, sperm or embryo, and a resulting change could be inherited by future generations. This possibility raises additional questions about consent, long-term effects and social consequences beyond the treatment of one individual.

  7. Q7. Consider the following statements about Casgevy: 1. It uses a patient's own blood-forming stem cells. 2. The cells are edited outside the body and returned after preparative treatment. 3. It demonstrates that CRISPR can treat every genetic disease. How many of the above statements are correct?

    1. Only one
    2. All three
    3. Only two
    4. None
    Show answer

    Correct answer: (C) Only two

    Explanation

    Correct Answer: (C). Statements 1 and 2 are correct: Casgevy uses the patient's own blood-forming stem cells, which are collected, edited outside the body and returned after preparative treatment. Statement 3 is incorrect; the therapy has specific indications and does not establish treatment for every genetic disease.

  8. Q8. According to the FDA label updated in July 2026, Casgevy is indicated in the United States for which pair of conditions?

    1. Cystic fibrosis and haemophilia
    2. Malaria and tuberculosis
    3. Diabetes and hypertension
    4. Sickle cell disease and transfusion-dependent beta-thalassemia
    Show answer

    Correct answer: (D) Sickle cell disease and transfusion-dependent beta-thalassemia

    Explanation

    Correct Answer: (D). The FDA label lists specified sickle cell disease and transfusion-dependent beta-thalassemia indications for Casgevy in the United States. This is a regulated use for defined conditions and age groups, not a general approval for all inherited disorders or all CRISPR products.

  9. Q9. Consider the following pairs: 1. Off-target editing : unintended change at a non-target DNA site 2. Delivery : getting the editing system to relevant cells 3. Somatic editing : necessarily heritable change How many of the above pairs are correctly matched?

    1. Only two
    2. Only one
    3. All three
    4. None
    Show answer

    Correct answer: (A) Only two

    Explanation

    Correct Answer: (A). The first two pairs are correct: off-target editing means an unintended change away from the intended DNA site, and delivery means getting the system to relevant cells. Somatic editing is not necessarily heritable, so the third pair is incorrect.

  10. Q10. Statement-I: CRISPR-Cas9 is described as programmable. Statement-II: Researchers can often retarget the system by changing the guide RNA sequence. Which one of the following is correct?

    1. Both correct; II does not explain I
    2. Both correct; II explains I
    3. I correct, II incorrect
    4. I incorrect, II correct
    Show answer

    Correct answer: (B) Both correct; II explains I

    Explanation

    Correct Answer: (B). Both statements are correct, and the second explains the first. A system is programmable in part because researchers can often change the guide RNA sequence to retarget Cas9. This flexibility does not mean the system is perfectly precise or free from unintended edits.

More practice MCQ sets

All MCQ sets