HSC Biology — Module 6
CRISPR Gene Editing — Flashcards & Quiz
CRISPR-Cas9 is a revolutionary gene-editing tool covered in HSC Biology Module 6 under biotechnology. It allows scientists to precisely cut and modify DNA sequences using a guide RNA and the Cas9 enzyme. You need to understand how CRISPR works, its applications in medicine (gene therapy, disease treatment) and agriculture (crop improvement), and the ethical debates surrounding germline editing. Extended response questions may ask you to evaluate the social and ethical implications of genetic technologies like CRISPR.
Key Points
- CRISPR-Cas9 is an adaptive immune system in prokaryotes, repurposed as the most precise gene-editing tool.
- A guide RNA (gRNA) directs Cas9 to a 20-nt complementary DNA target adjacent to a PAM sequence, where Cas9 makes a double-strand break.
- The cell repairs the break via non-homologous end joining (NHEJ, error-prone, knockouts) or homology-directed repair (HDR, template-based, precise edits).
- Applications: disease models, gene therapy (sickle cell, beta-thalassaemia trials), agriculture (disease-resistant crops), conservation (gene drives).
- HSC evaluation: compare precision vs off-target effects, cost, bioethics (germline edits in humans), and regulation.
- Key difference from older tools (ZFNs, TALENs): CRISPR uses RNA-guided targeting, which is cheaper and faster to design.
Common Mistakes to Avoid
- Writing that Cas9 edits RNA — Cas9 cuts DNA; RNA is the guide molecule that directs it.
- Forgetting the PAM sequence is required — Cas9 only cuts DNA adjacent to a specific PAM (usually NGG for SpCas9).
- Claiming CRISPR is 100% precise — off-target effects exist and are a real limitation, especially for clinical applications.
- Confusing knockout (NHEJ repair) with knock-in (HDR repair with a template) — they produce very different outcomes.
- Assuming all CRISPR edits are germline (heritable) — somatic edits are not passed to offspring and face different ethical considerations.
Exam Strategy
HSC Module 5/6 CRISPR questions are almost always evaluation tasks: "assess the impact of CRISPR on medicine/agriculture/bioethics". Use a structured argument: (1) describe the mechanism concisely (gRNA → Cas9 → DSB → NHEJ or HDR), (2) name two specific applications with outcomes, (3) evaluate benefits vs risks (cost, precision, off-target, germline ethics), (4) conclude with a justified judgement. Named examples like sickle cell clinical trials strengthen the response.
Sample Flashcards
Q1: What is a transgenic organism?
A transgenic organism contains a gene (transgene) from a different species, inserted using genetic engineering. The transgene is expressed, giving the organism a new trait.
Q2: Describe CRISPR-Cas9 gene editing.
CRISPR-Cas9 is a precise gene editing tool. A guide RNA directs the Cas9 enzyme to a specific DNA sequence, where it cuts both strands. The cell's repair mechanisms then delete, replace, or insert DNA at the cut site. It is faster, cheaper and more accurate than older techniques.
Q3: Compare reproductive and therapeutic cloning.
Reproductive cloning: creates a genetically identical organism (e.g. Dolly the sheep) by inserting a somatic cell nucleus into an enucleated egg, then implanting the embryo. Therapeutic cloning: creates embryonic stem cells for medical treatment — the embryo is NOT implanted. Used to grow replacement tissues.
Q4: What is gene therapy?
Gene therapy treats genetic disorders by introducing, altering or replacing genes within a patient's cells. Somatic gene therapy targets body cells (not heritable). Germline gene therapy targets egg/sperm cells (heritable but ethically controversial and banned in many countries).
Q5: What are the ethical concerns surrounding genetic technologies?
Key concerns: 1) Germline editing affects future generations without consent. 2) "Designer babies" and eugenics risks. 3) Ecological impacts of GMOs. 4) Equitable access to gene therapies (cost). 5) Animal welfare in cloning. 6) Patenting of genes and organisms.
Sample Quiz Questions
Q1: Transgenic organisms contain genes from a different species.
Answer: TRUE
A transgenic organism has a gene (transgene) from another species inserted into its genome using genetic engineering techniques.
Q2: CRISPR-Cas9 can only delete genes, not insert or replace them.
Answer: FALSE
CRISPR-Cas9 can delete, replace, or insert DNA sequences at specific locations. Its versatility is a key advantage over older techniques.
Q3: Therapeutic cloning creates an embryo that is implanted and grows into a full organism.
Answer: FALSE
Therapeutic cloning creates embryonic stem cells for medical treatment — the embryo is NOT implanted. Reproductive cloning implants the embryo to produce a whole organism.
Revision Tip
Evaluative responses need both mechanism and application recall — build a Revizi deck covering the mechanism diagram and 3 named CRISPR case studies, then practise the "describe → apply → evaluate" structure.
Related Concepts
Last updated: March 2026 · 5 flashcards · 5 quiz questions