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Q17 - Predicting Reading-Frame Effects of CRISPR-Cas9 Indels

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Recombinant DNA & Biotechnology Techniques

In recent years, a genome editing technology called the CRISPR-Cas9 method has been widely used for biology research. In the CRISPR-Cas9 method, an enzyme called Cas9 is guided to the target gene by forming a complex with a guide RNA with a sequence complementary to a part of the target gene. Then, Cas9 cleaves the double- stranded DNA of the target gene specifically with its activity of cleaving double-stranded DNA. Cas9 recognizes a 3-base sequence (NGG) called PAM sequence and cuts the DNA strand 3 to 4 bases upstream of PAM. The cleaved DNA chain is repaired by the DNA repair system, but at that time, a few bases are frequently deleted or inserted. The CRISPR-Cas9 method was applied by targeting the region close to the translation start codon of the most upstream exon of a gene encoding enzyme A of a certain animal. The base sequence of the target region was determined for each of the four mutants obtained (Figure 1).

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. It is highly likely that the activity of enzyme A is retained in mutant 1.
B. It is highly likely that the activity of enzyme A is retained in mutant 2.
C. It is possible that the activity of enzyme A is retained in mutant 3.
D. It is highly likely that the activity of enzyme A is lost in mutant 4.
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Question reproduced from IBO 2020, Theoretical Exam 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)