Gene Editing and CRISPR
In 2023, the US FDA approved CRISPR therapy Casgevy, the first treatment to permanently cure sickle cell disease in over 90% of patients using a single gene edit.
Printable Worksheets
Print or save as PDF, or build a custom worksheet from any module's questions.
Q1 · What do you already know about gene editing? Have you heard of CRISPR?
Think about what you have read or seen about scientists editing genes in plants, animals or humans.
Q2 · If scientists could safely edit human embryos to prevent genetic diseases, should they be allowed to do so? Why or why not?
Consider both the potential to eliminate suffering and the ethical concerns about altering human DNA.
● Know
- That gene editing means making precise changes to DNA
- That CRISPR-Cas9 is a targeted gene-editing tool
- Some potential applications of gene editing in medicine and agriculture
- That gene editing has limitations and ethical concerns
● Understand
- How CRISPR-Cas9 allows scientists to target specific genes
- Why gene editing is more precise than older genetic technologies
- The difference between editing somatic cells and germline cells
● Can do
- Explain how CRISPR-Cas9 works in simple terms
- Evaluate one benefit and one limitation of a CRISPR application
- Compare gene editing to selective breeding and genetic modification
A patient with a lifelong blood disorder receives an injection; one year later, their bone marrow is producing normal haemoglobin for the first time, because a microscopic protein corrected a single letter in their DNA. CRISPR-Cas9 is the revolutionary gene editing technology that made this possible, derived from a bacterial immune system. It works like molecular scissors guided by GPS. A piece of guide RNA is designed to match a specific DNA sequence. This RNA attaches to the Cas9 protein and leads it to the target site in the genome, where Cas9 cuts both strands of the DNA. The cell's natural repair mechanisms then kick in, and scientists can harness these repairs to delete genes, correct mutations or insert new genetic material.
What makes CRISPR transformative is its simplicity, speed and low cost. Previous gene editing tools required complex protein engineering for each new target and cost tens of thousands of dollars. CRISPR requires only a short RNA sequence that can be synthesised for a few dollars. Laboratories worldwide can now edit genes in days rather than months, opening research and therapeutic possibilities that were science fiction a decade ago.
In 2023, the first CRISPR-based medicine was approved in several countries for sickle cell disease and beta-thalassemia. Doctors extract a patient's blood stem cells, use CRISPR to reactivate the fetal haemoglobin gene, and return the edited cells to the patient. Early trial results show that many patients are effectively cured, producing normal blood cells for the first time in their lives.
Australian research: Scientists at the Children's Medical Research Institute in Sydney use CRISPR to study and potentially treat muscular dystrophy. By correcting the genetic mutation in patient cells grown in the lab, they hope to develop therapies that could one day be delivered directly to muscles, sparing children from progressive muscle wasting.
Many students think gene editing is still science fiction or only happens in movies. In reality, CRISPR therapies are already in clinical trials and one has been approved for human use. Gene-edited crops are being grown, and gene drives are being tested to control mosquito-borne diseases. The technology is here now, and society must grapple with its implications in real time.
CRISPR gene editing was adapted from a bacterial immune system. Before reading on, predict: what do bacteria use CRISPR to defend against?
How close was your prediction?
Nice calibration, your intuition is good for this kind of problem.
Good, being surprised is the point. This answer is worth remembering.
Gene editing can be applied to two types of cells, with radically different consequences. Somatic editing changes the DNA of body cells, skin, blood, muscle or nerve cells. The changes help the treated individual but are not passed to their children. Germline editing changes the DNA of sperm, eggs or embryos. These changes are inherited by every descendant, permanently altering the human gene pool.
Most scientists and ethicists support somatic editing for serious diseases, provided safety and consent are assured. Germline editing is far more controversial. The changes are irreversible, the long-term effects are unknown, and the individuals affected cannot consent. Many countries have banned or restricted germline editing, though the technology to do it exists. The debate is not about whether we can edit embryos, we can, but whether we should.
In 2018, a Chinese scientist announced the birth of twin girls whose embryos had been edited using CRISPR to resist HIV infection. The experiment was widely condemned as unethical, illegal and scientifically premature. The edits may have caused unintended changes elsewhere in the genome, and the girls had no ability to consent to becoming the world's first gene-edited humans.
Australian policy: Australia prohibits heritable germline modification under the Prohibition of Human Cloning for Reproduction Act 2002. Somatic gene therapy is permitted under strict regulatory oversight by the Office of the Gene Technology Regulator and the Therapeutic Goods Administration. This framework aims to allow beneficial therapies while preventing reckless experiments.
Beyond medicine, CRISPR is transforming agriculture and conservation. Scientists are developing crops with higher yields, better nutrition and resistance to drought and pests by editing their native genes rather than inserting foreign DNA. These 'gene-edited' crops are regulated differently from transgenic GMOs in many countries because they do not contain DNA from other species.
In conservation, gene drives are being explored as a way to control invasive species or suppress disease vectors. A gene drive ensures that a particular gene is inherited by nearly all offspring rather than the usual 50%. In theory, a gene drive could spread infertility through a population of invasive mice or render mosquitoes unable to transmit malaria. The power is enormous, and so are the ecological risks if something goes wrong.
Researchers in Australia are developing a gene drive to control invasive cane toads, which devastate native wildlife. The idea is to release gene-edited toads that produce only male offspring, causing the population to crash over time. Before any release, scientists must model the ecological consequences carefully, because an accidental spread beyond the target area could have unpredictable effects.
Australian biosecurity: CSIRO is investigating gene editing as a tool to protect Australian agriculture from pests and diseases. By editing the genes of crop plants to resist pathogens, or by developing genetic biocontrols for invasive species, they aim to reduce reliance on chemical pesticides while preserving Australia's unique ecosystems.
Australian regulatory oversight of gene technology is among the most rigorous in the world. The Office of the Gene Technology Regulator (OGTR), based in Canberra, assesses all genetically modified organisms before they can be released. CSIRO, Australia's national science agency, conducts extensive gene-editing research on crops and livestock but must obtain OGTR approval for any field trials. In 2019, Australian researchers at the University of Queensland used CRISPR to develop a rapid diagnostic test for COVID-19, demonstrating how the same technology can be applied outside of gene editing itself. The National Health and Medical Research Council (NHMRC) oversees ethical guidelines for human gene therapy research, ensuring that Australian scientists operate within internationally accepted boundaries.
Wrong: "CRISPR can perfectly edit any gene with no mistakes."
Right: CRISPR is precise but not perfect. Off-target effects can occur, so every edit must be carefully validated before clinical or environmental use.
Wrong: CRISPR is precise but not perfect. Off-target effects remain a significant challenge. Scientists must carefully validate each edit and consider unintended consequences before clinical or environmental use.
Right: CRISPR is highly precise, but off-target effects remain a challenge. Scientists must validate edits and consider unintended consequences.
Wrong: "Gene editing and genetic modification are exactly the same thing."
Right: Genetic modification typically involves inserting foreign DNA from another species. Gene editing makes precise changes within an organism's existing DNA without necessarily adding foreign genes.
Wrong: Genetic modification typically involves inserting DNA from another species. Gene editing makes precise changes within an organism's existing DNA and does not necessarily add foreign genes.
Right: Gene editing alters existing DNA within an organism. Genetic modification usually involves adding DNA from a different species. They are related but distinct technologies.
Sickle Cell Disease and the First CRISPR Therapy
Sickle cell disease affects approximately 100,000 people in the United States and millions worldwide, including Aboriginal and Torres Strait Islander populations in Australia where prevalence is higher than in the general community. The disease is caused by a single DNA mutation that changes one amino acid in haemoglobin.
In 2023, regulators in the UK and USA approved Casgevy (exagamglogene autotemcel), the world's first CRISPR-based medicine. The treatment works by editing blood stem cells to reactivate production of fetal haemoglobin, compensating for the defective adult haemoglobin. For patients who have endured a lifetime of pain crises and organ damage, this represents a potential cure, not just management, of their genetic disease. The approval marked a historic milestone: humanity had moved from reading the genetic code to rewriting it therapeutically.
Evaluate CRISPR Applications
1 Scientists use CRISPR to edit blood stem cells from a patient with sickle cell disease, enabling them to produce healthy red blood cells. Identify one benefit and one limitation of this approach.
2 Australian researchers develop a gene-edited wheat variety that survives with 30% less water. Explain one benefit to Australian farmers and one potential concern about releasing this wheat into the environment.
3 A research team proposes using CRISPR to make Australian feral cats sterile, so their population declines over time. Identify one potential benefit and one significant risk of this approach.
Compare Genetic Technologies
1 Explain how selective breeding and CRISPR gene editing both aim to improve traits, but achieve this in fundamentally different ways.
2 Genetic modification (GM) often involves inserting a gene from one species into another. Gene editing can make precise changes without adding foreign DNA. Explain why some people view gene editing as more acceptable than GM, even though both alter an organism's DNA.
3 A scientist claims that because gene editing is more precise than selective breeding, it should replace traditional breeding methods entirely. Evaluate this claim, considering at least one advantage of selective breeding that CRISPR cannot easily replicate.
Copy Into Your Book
▼Gene Editing Basics
- Gene editing = precise changes to DNA
- CRISPR-Cas9 = guide molecule + cutting enzyme
- Guide RNA finds the target sequence
- Cas9 cuts DNA; cell repairs it
Applications
- Disease treatment: sickle cell, cancers
- Agriculture: drought-resistant crops
- Conservation: gene drives for pest control
- Australia: CSIRO wheat and barley research
Limitations
- Off-target effects: cutting wrong DNA
- Ethical concerns with human embryos
- Ecological risks of gene drives
- Regulatory oversight required
Comparing Technologies
- Selective breeding = choosing parents
- GM = inserting foreign DNA
- Gene editing = precise internal changes
- Germline editing affects future generations
At the start of this lesson you heard that scientists at Colossal Biosciences are using CRISPR to edit thylacine genes into living marsupial cells, trying to bring back an animal that has been extinct since 1936. That example was chosen to show you that CRISPR can do something that seemed like pure science fiction just a decade ago.
Now that you understand how CRISPR-Cas9 finds a target sequence, cuts the DNA and allows edits to be made, explain how that thylacine project could work in principle. What does knowing the mechanism make you think differently about, the possibility, the risks, or the ethics?
Q1. Describe how CRISPR-Cas9 works in simple terms. What makes it different from older genetic technologies? 4 MARKS
Q2. Choose one application of CRISPR (disease treatment, agriculture, or conservation). Explain the potential benefit and one limitation. 4 MARKS
Q3. Compare CRISPR to selective breeding and genetic modification. How are they similar and how do they differ? 4 MARKS
Revisit Your Initial Thinking
Go back to your Think First responses at the top of the lesson.
- Did you predict that gene editing could treat diseases by fixing faulty DNA?
- Has your view on whether scientists should edit human embryos changed after learning about germline editing?
- Write one sentence explaining why CRISPR is described as a "molecular scissors" tool.
Model answers (click to reveal)
Comprehensive Answers
▼Activity 1, Evaluate CRISPR Applications
1. Sickle cell therapy: Benefit, can potentially cure a life-threatening genetic disease rather than just managing symptoms [1 mark]. Limitation, the treatment is extremely expensive, requires specialised medical facilities, and may not be accessible to all patients who need it [1 mark].
2. Drought-resistant wheat: Benefit, Australian farmers could maintain yields during droughts, improving food security and farm income [1 mark]. Environmental concern, the edited wheat might cross-breed with wild relatives or alter soil microbiome interactions in unpredictable ways [1 mark].
3. Sterile feral cats: Benefit, could reduce the devastating impact of feral cats on Australia's native wildlife, which kill billions of animals annually [1 mark]. Risk, the gene drive could spread to non-target species or have cascading ecological effects that are difficult to predict or reverse [1 mark].
Activity 2, Compare Genetic Technologies
1. Selective breeding chooses parents with desirable traits and relies on natural genetic recombination during reproduction [1 mark]. CRISPR directly alters DNA sequences in a laboratory, bypassing generations of breeding and achieving precise, predictable changes [1 mark].
2. Gene editing makes changes within an organism's own DNA without necessarily adding foreign genetic material [1 mark]. This means the resulting organism might have a genetic profile that could theoretically arise through natural mutation, which some people find more acceptable than combining DNA from different species [1 mark].
3. The claim is overstated [1 mark]. Selective breeding has safely improved crops and livestock for thousands of years without laboratory intervention, and it often improves multiple traits simultaneously through natural polygenic variation [1 mark]. CRISPR is powerful for single-gene changes but does not easily replicate the complex, coordinated improvements that selective breeding can achieve across many genes [1 mark]. Both tools have roles in modern agriculture.
Multiple Choice
1. BCRISPR-Cas9 is a tool for making precise changes to DNA. It is not an antibiotic, sequencing method or cloning technique.
2. CCRISPR is being used to treat genetic diseases like sickle cell anaemia by correcting the faulty gene in a patient's cells.
3. AAn off-target effect occurs when CRISPR cuts DNA at an unintended location, potentially disrupting another gene.
4. DEditing embryos (germline editing) is controversial because the genetic changes would be inherited by all descendants.
5. BReleasing gene-edited mosquitoes could have unexpected effects on food webs, predator-prey relationships and ecosystem balance.
Short Answer Model Answers
Q6 (4 marks): CRISPR-Cas9 uses a guide RNA molecule to locate a specific DNA sequence [1 mark]. The Cas9 enzyme then cuts the DNA at that precise location [1 mark]. The cell's natural repair machinery fixes the break, and scientists can direct this repair to make a desired change [1 mark]. Unlike older technologies such as selective breeding (which is slow and indirect) or genetic modification (which inserts foreign DNA), CRISPR can make precise, targeted changes directly at a specific gene [1 mark].
Q7 (4 marks): Example answer, disease treatment: CRISPR can be used to treat sickle cell disease by editing blood stem cells so they produce healthy haemoglobin [1 mark]. The potential benefit is that patients could be cured of a painful, life-shortening genetic disease rather than just managing symptoms [1 mark]. One limitation is that the treatment is currently very expensive and requires highly specialised medical facilities, making it inaccessible to many patients globally [1 mark]. Additionally, off-target effects could cause unintended changes to other genes [1 mark].
Q8 (4 marks): All three technologies aim to improve the traits of organisms [1 mark]. Selective breeding achieves this by choosing which organisms reproduce, without directly altering DNA [1 mark]. Genetic modification inserts genes from other species into an organism's genome [1 mark]. CRISPR gene editing makes precise changes within an organism's existing DNA, allowing specific genes to be altered, removed or corrected without necessarily adding foreign genetic material [1 mark].
Jump Through Gene Editing!
Climb platforms using your knowledge of CRISPR, gene editing and genetic technologies. Pool: Lesson 9.