[Campbell Biology P.410] Figure 17.28 illustrates two distinct pathways for repairing broken... | Practice Question

Figure 17.28 illustrates two distinct pathways for repairing broken DNA strands after Cas9 cleavage. What is the fundamental difference in the outcome of these two pathways for the target gene?

  • A: One pathway repairs the gene to its original functional state, while the other always results in the deletion of the entire gene.
  • B: One pathway leads to a nonfunctional gene through random nucleotide changes, whereas the other pathway corrects a mutation by synthesizing the proper sequence from a template.
  • C: Both pathways lead to a functional gene, but one uses a normal template while the other relies on random insertion.
  • D: Both pathways result in gene knockout, but one is more efficient than the other.

Explanation

Figure 17.28, Step 3, clearly describes two distinct repair pathways. The left pathway states 'repair enzymes insert and/or delete random nucleotides, making the gene nonfunctional' a gene knockout . The right pathway states 'If the target gene has a mutation, it can be repaired by providing a normal copy of the gene. Repair enzymes use the normal gene as a template and synthesize the correct gene sequence.' This highlights the fundamental difference in outcomes: one leads to a nonfunctional gene, and the other to a corrected, functional gene.