📚 Learning Guide
CRISPR-Cas9 Genome Editing
hard

If CRISPR-Cas9 successfully edits a gene to confer antibiotic resistance in bacteria, what is the most likely underlying mechanism that enables this change?

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Choose the Best Answer

A

The Cas9 protein randomly alters DNA sequences throughout the genome.

B

The guide RNA directs the Cas9 to a specific DNA sequence, enabling precise cuts.

C

The PAM site is a non-specific region that allows multiple edits at once.

D

The bacteria naturally develop resistance without any genetic modifications.

Understanding the Answer

Let's break down why this is correct

Answer

CRISPR‑Cas9 cuts a specific spot in the bacterial DNA where the antibiotic‑resistance gene is to be inserted. The Cas9 enzyme, guided by a short RNA sequence, creates a double‑strand break exactly at that site. The cell then repairs the break using a supplied DNA template that carries the resistance gene, a process called homologous recombination. In this way the new gene is precisely copied into the genome, giving the bacteria the ability to survive the antibiotic. For example, a plasmid containing a chloramphenicol‑resistance cassette can be inserted into the *gyrA* gene of *E.

Detailed Explanation

The guide RNA is made to match a specific DNA sequence. Other options are incorrect because Some think Cas9 changes DNA everywhere; The PAM site is a short DNA motif that Cas9 needs to bind.

Key Concepts

CRISPR-Cas9 Mechanism
Gene Editing Applications
Antibiotic Resistance
Topic

CRISPR-Cas9 Genome Editing

Difficulty

hard level question

Cognitive Level

understand

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