Grade 7 · English for Korean learners
Bacteria have no laboratories, yet some carry a molecular defence system that scientists have turned into a powerful research tool. CRISPR-based editing can target DNA, the molecule containing much of a cell’s inherited information. That sounds like correcting a spelling mistake, until one remembers that the document is alive, copied repeatedly, and connected to thousands of other instructions. Editing can help researchers investigate genes and can treat certain diseases. It can also produce unintended changes. The important questions are how the tool finds its target, what the cell does afterwards, and who should decide when changing genetic information is justified.
In the News
US regulators approve two gene therapies for sickle cell disease — The Guardian, 8 December 2023. One used CRISPR. Approval marked a medical milestone.
US doctors rewrite DNA of infant with severe genetic disorder in medical first — The Guardian, 15 May 2025. Customised editing treated one infant. Monitoring remained essential.
Biologist whose innovation saved the life of British teenager wins $3m Breakthrough prize — The Guardian, 5 April 2025. Base-editing research received recognition. Delivery remains difficult.
What do you think?
1] What happens when one letter in an instruction changes?
2] Why can changing a small part affect a whole system?
3] How could a copied message preserve an error?
4] Why should a repair be checked afterwards?
5] What makes a change reversible or permanent?
6] How could a tiny tool find one place in a large object?
7] Why might similar patterns cause confusion?
8] What would make a treatment worth a serious risk?
9] Who should decide about a change affecting future people?
10] Why are test results from one person limited?
11] How might a useful change also cause harm?
12] Why can delivering a tool be harder than designing it?
13] What should count as informed permission?
14] How could a farmer judge a new crop?
15] Why do living systems respond differently?
16] When should a promising experiment remain an experiment?
17] Why might a cheap tool lead to an expensive treatment?
18] What information should a safety test collect?
19] How can a benefit be shared fairly?
20] Why should a repair target a known problem rather than a fashionable preference?
Did You Know?
1] CRISPR systems evolved in microbes as defence against genetic invaders such as viruses.
2] The 2020 Nobel Prize in Chemistry recognised Emmanuelle Charpentier and Jennifer Doudna’s work on genome editing.
3] Mature human red blood cells have no nucleus; some therapies instead edit the stem cells that produce blood cells.
4] Some bacteria keep fragments of past invaders’ DNA, rather like a microscopic record of unwelcome visitors.
Vocabulary
- inherited — 유전된
- sequence — 염기 배열
- instruction — 지시 정보
- copy — 복사하다
- target — 표적
- match — 일치하다
- cut — 자르다
- repair — 복구하다
- insert — 삽입하다
- deletion — 삭제
- unintended — 의도하지 않은
- delivery — 전달
- chromosome — 염색체
- stem cell — 줄기세포
- blood cell — 혈액 세포
- bone marrow — 골수
- nucleus — 세포핵
- protein — 단백질
- enzyme — 효소
- trait — 형질
- crop — 작물
- environmental influences — 환경의 영향
- trial — 시험
- monitoring — 경과 관찰
- consent — 동의
- heritable — 다음 세대로 유전될 수 있는
- offspring — 자손
- access — 이용 기회
- uncertainty — 불확실성
- oversight — 감독
Glossary
DNA — DNA stores inherited biological information. Its sequence helps cells make and regulate molecules. Changes can alter cell behaviour. 디옥시리보핵산.
Gene — A gene is a functional region of DNA. Many genes provide instructions for proteins. Other regions help regulate their activity. 유전자.
Genome — A genome is an organism’s complete genetic material. It includes genes and other sequences. Context matters when editing it. 유전체.
Mutation — A mutation is a change in DNA sequence. Some changes affect function. Others have little detectable effect. 돌연변이.
CRISPR — The name refers to repeated DNA sequences in microbial defence systems. Related proteins help target genetic material. Scientists adapted these systems for editing. 크리스퍼.
Guide RNA — A guide RNA helps direct an editing protein. Its sequence matches a chosen DNA target. Matching is powerful but not infallible. 안내 RNA.
Cas9 — Cas9 is a protein that can cut DNA. A guide directs it to suitable targets. The cell then responds to the break. 카스9 단백질.
Base editing — Base editing changes selected DNA letters using an adapted targeting system. It usually avoids a full double-strand break. It still has limits and possible errors. 염기 교정.
Somatic editing — Somatic editing changes ordinary body cells. It is intended to affect the treated individual. It does not intentionally alter inherited reproductive cells. 체세포 유전자 교정.
Germline editing — Germline editing concerns reproductive cells or their precursors. Editing embryos for reproduction can create heritable changes. Future generations may be affected. 생식세포 계열 유전자 교정.
DNA and a Defence Borrowed from Bacteria
DNA contains a sequence of chemical units commonly represented by the letters A, T, C, and G. In many cells it sits mainly inside a nucleus, organised into chromosomes. Genes are functional regions within this material, while other sequences help regulate activity. Cells use genetic information to produce molecules, including proteins that support structure, signalling, and chemical reactions. DNA is therefore not a complete miniature drawing of an organism. Its effects depend on cellular machinery and environment. A sequence change may alter an important protein, change when a gene is active, or have little detectable effect. Context determines the outcome.
1] What do DNA letters represent?
2] Why does a sequence change not always have the same effect?
A mutation is a change in DNA sequence. It can arise during copying, through damage, or through other biological processes. Some mutations contribute to disease, while others are neutral or useful in particular circumstances. Inherited mutations can pass through reproductive cells to offspring. Changes acquired in ordinary body cells generally affect the individual or a group of cells instead. Many traits involve numerous genes interacting with environmental influences. Changing one sequence therefore does not normally let a scientist select any complex characteristic at will. Biology is a connected system. A simple-looking edit may require careful investigation of several consequences before its value becomes clear.
1] How can mutations arise?
2] Why are complex traits difficult to change predictably?
Some bacteria use CRISPR-associated systems to defend themselves against genetic invaders such as viruses. They can retain short pieces of an invader’s genetic material and use related information to recognise a later attack. Associated proteins then help target matching material. This defence is not human-style memory or conscious planning. It is a molecular mechanism shaped by evolution. Scientists studied such systems and adapted their targeting ability for laboratory work. The surprising origin matters: a tool used in advanced medicine began with investigating microbial biology. Basic research can reveal useful mechanisms without starting from a plan to build a particular human treatment.
1] What does microbial CRISPR defence target?
2] Why is it misleading to call the defence conscious memory?
Researchers transformed a natural targeting system into a programmable laboratory tool. Work by Emmanuelle Charpentier, Jennifer Doudna, and many other scientists helped establish CRISPR-based genome editing. Charpentier and Doudna received the Nobel Prize in Chemistry in 2020. A key advantage is that changing the guide sequence can redirect an editing system toward a different target. Earlier editing methods existed, but this approach made many experiments faster and easier to organise. Easier targeting does not mean that every resulting change is safe or useful. The historical achievement concerns a powerful method. Its applications still require separate evidence about delivery, outcomes, and possible harm.
1] What makes the targeting system programmable?
2] Why does a useful method not validate every application?
Targeting, Cutting, and Cellular Repair
In a common CRISPR-Cas9 system, a guide RNA carries a sequence designed to match a chosen DNA region. Cas9 uses the guide to locate a suitable target, including a required nearby recognition sequence. Matching helps the protein distinguish among many possible locations. However, closely similar sequences can sometimes be recognised unintentionally. Researchers design guides carefully and test their behaviour rather than assuming perfect accuracy. The system is often compared with molecular scissors, but scissors alone do not explain the search process. The guide and recognition requirements are essential. A cutting tool becomes useful only when its destination can be controlled and checked.
1] What does guide RNA contribute?
2] Why must researchers test for similar unintended targets?
Cas9 can make a break across both strands of DNA. The cell then attempts to repair the damage using its own machinery. One repair pathway joins the broken ends and may introduce small insertions or deletions. Such changes can disrupt a gene or regulatory region. Scientists can use that effect to investigate what happens when a function is reduced. Cutting is therefore not the same as neatly replacing a faulty instruction with a correct one. The final sequence depends on the repair process. Researchers must measure what actually happened in the treated cells. A planned edit and a verified result are different stages of the experiment.
1] How can repair disrupt a gene?
2] Why must the final DNA sequence be checked?
Under suitable conditions, cells can use supplied template information during repair to introduce a chosen sequence change. This offers a way to make more specific edits, but it does not work equally well in every cell type or situation. Efficiency, timing, and unwanted changes remain concerns. Some cells may receive the intended edit while others remain unchanged or acquire different alterations. A mixed population complicates interpretation and medical use. Researchers therefore examine both the proportion of successfully edited cells and the range of outcomes. Precision is an achievement to demonstrate with evidence, not a quality guaranteed by calling the tool precise in a description.
1] How can template information support a chosen edit?
2] Why does a mixed cell population complicate interpretation?
Base editors combine a targeting system with an enzyme that changes selected DNA bases. Many designs avoid making a full double-strand break, though they still have possible unwanted effects and restrictions on which changes they can make. Prime editing uses another adapted system and a specialised guide to support a wider range of changes. These methods expand the toolkit rather than replacing every earlier technique. The appropriate method depends on the target, cell type, desired change, and delivery. ‘Editing’ therefore covers several molecular approaches. Saying that all of them merely cut out a gene misses important differences in both mechanism and possible outcomes.
1] How does base editing differ from ordinary Cas9 cutting?
2] Why are several editing methods useful?
Research, Treatment, and Agriculture
Researchers can edit cells to investigate a gene’s function. If changing a sequence alters a measured process, that provides a clue about the sequence’s role. Suitable controls are essential because handling cells, delivering material, or introducing other changes can also affect results. Scientists compare edited cells with relevant unedited or differently treated cells. They repeat experiments and use additional methods to test explanations. A changed result does not always prove a simple direct relationship. Networks of genes and proteins can produce indirect effects. Genome editing is powerful research equipment, but interpreting an experiment still requires careful reasoning about causes and alternatives.
1] Why does an editing experiment need controls?
2] How could an observed effect be indirect?
In December 2023, the US Food and Drug Administration approved Casgevy for certain people aged 12 and older with sickle cell disease. This was the first FDA-approved treatment using CRISPR-based editing. The therapy edits blood-forming stem cells outside the body, then returns them to bone marrow after preparation. It changes a regulatory region associated with BCL11A so developing blood cells produce more fetal haemoglobin. That protein can reduce the effects of sickling. The treatment does not simply repair every cell’s original disease mutation. Its mechanism changes gene regulation in particular cells. The date and age range here describe the original approval, rather than every later indication.
1] What cells are edited in Casgevy?
2] How does increased fetal haemoglobin help explain the treatment?
Editing outside the body allows cells to be examined before they are returned. However, the full treatment can involve intensive preparation, hospital care, and long-term follow-up. Risks may come from the editing, the delivery process, or associated treatment such as chemotherapy. In-body editing presents another challenge: getting the machinery into the correct cells in sufficient amounts. In 2025, researchers reported personalised base editing for an infant with severe CPS1 deficiency, targeting liver cells to improve ammonia processing. The early result was promising, but one patient cannot establish every long-term outcome. A successful molecular design still needs safe delivery and careful monitoring in an actual person.
1] Why can an editing treatment remain demanding?
2] Why does one promising patient result require continued study?
Crop editing can change selected characteristics, such as resistance to a disease or the composition of a harvested product. Researchers must establish the biological effect and test performance under realistic growing conditions. A useful laboratory change may behave differently under drought, pests, or varied soils. Edited plants also interact with farming systems and surrounding organisms. Food safety, ecological effects, seed access, and public choices require attention. Not every edited crop involves adding DNA from another species, but the method alone does not settle whether a particular product is beneficial. Assessment should focus on the actual change, evidence, and conditions of use rather than a single reassuring label.
1] Why must edited crops be tested under realistic conditions?
2] Why does the editing method alone not settle a product’s value?
Safety, Inheritance, and Fair Access
Unintended editing can occur at a different DNA location, called an off-target site. Unexpected outcomes can also occur at the intended location, including larger changes than researchers planned. These are distinct problems and both require investigation. Testing may examine sequence changes, cell behaviour, and possible effects on growth or health. No test can establish every lifetime outcome immediately. Researchers therefore combine laboratory evidence, carefully designed trials, and follow-up. Reducing one risk does not automatically remove another. A tool may find the intended site accurately while the repair still produces an unwanted result. Safety assessment must follow the process through to its biological consequences.
1] How do off-target and unexpected on-target changes differ?
2] Why must safety assessment include cell behaviour?
Somatic editing targets ordinary body cells and is intended to affect the treated person. Editing reproductive cells or embryos used to establish a pregnancy could instead create heritable changes affecting later generations. This distinction changes the ethical stakes. Future children cannot consent to experimental changes made before their existence, and unintended effects might persist through inheritance. The World Health Organization has emphasised the need for strong oversight of human genome editing. Heritable reproductive use raises major unresolved safety and ethical concerns. Treating it as simply another way to deliver an established therapy would obscure those differences. Clinical benefit in somatic cells does not establish safe reproductive use.
1] Why can heritable editing affect people beyond one patient?
2] Why does somatic-treatment success not establish reproductive safety?
Informed consent requires a person to understand the proposed treatment, important risks, alternatives, and remaining uncertainty. A hopeful family should not be given the impression that an experimental method guarantees a cure. Independent review and transparent trial reporting help protect participants and improve evidence. Fair access is another challenge. A molecular tool may be relatively inexpensive while the complete treatment requires specialist manufacturing, hospital services, and prolonged care. People in regions with limited resources may have the greatest need yet the least access. Technical success therefore does not finish the public-health task. Benefits depend on delivery systems, funding, and decisions about who can receive care.
1] What must informed consent communicate?
2] Why can an inexpensive tool lead to an expensive treatment?
Future editing methods may improve targeting, delivery, and the range of treatable diseases. These are plausible directions, not promises that every condition will become easy to cure. Diseases involving many genes, widespread tissues, or complex environmental effects present different challenges from a well-understood single-gene disorder. Students can assess a claim by asking which cells are changed, what mechanism is proposed, what evidence exists, and what remains unknown. The same questions help distinguish research, approved treatment, and speculation. Changing life is a substantial responsibility. Useful progress combines molecular understanding with reliable outcomes, honest communication, public oversight, and attention to the people affected by the technology.
1] Why are some diseases harder editing targets than others?
2] What questions help assess a claim about a future treatment?
Homework
Writing tasks
1] Write approximately one page. Explain why one changed letter can matter in some instructions but not others.
2] Write approximately one page. Describe how a guide can help a tool find a target and how matching can fail.
3] Write approximately one page. Explain why cutting DNA differs from guaranteeing a repair.
4] Write approximately one page. Discuss why researchers should check both intended and unintended changes.
5] Write approximately one page. Explain the role of controls in testing a gene’s function.
6] Write approximately one page. Compare editing cells outside the body with editing inside it.
7] Write approximately one page. Describe why one promising medical result does not establish every outcome.
8] Write approximately one page. Argue what evidence a farmer should require before adopting an edited crop.
9] Write approximately one page. Explain why consent and inheritance create different ethical questions.
10] Write approximately one page. Discuss how a successful treatment could become accessible to more patients.
Debate topics
1] Should public funding prioritise editing treatments for severe disease?
Side A — Yes, because: 1) unmet needs are large; 2) research can support later therapies; 3) shared funding may improve access.
Side B — No, because: 1) other care also needs resources; 2) some methods remain uncertain; 3) lower-cost prevention may help more people.
2] Should approved edited crops be assessed by their particular traits?
Side A — Yes, because: 1) changes have different effects; 2) evidence can guide decisions; 3) labels alone hide useful distinctions.
Side B — No, because: 1) shared monitoring can simplify oversight; 2) wider farming effects need common rules; 3) consumers may want process information too.
3] Should editing trials require prolonged follow-up?
Side A — Yes, because: 1) delayed effects matter; 2) durability needs evidence; 3) later patients benefit from reliable records.
Side B — No, because: 1) monitoring burdens participants; 2) costs can limit trials; 3) requirements should match the actual risk.
Test questions
Answer the following questions in full sentences. If you don’t know the right answer, add a (?) mark, and later we can look at it together.
1] What information does DNA contain?
2] How does a gene differ from a genome?
3] What is a mutation?
4] Why are complex traits difficult editing targets?
5] What is the microbial origin of CRISPR systems?
6] What did the 2020 chemistry Nobel Prize recognise?
7] What does guide RNA do?
8] Why are nearby recognition requirements important?
9] What happens after Cas9 makes a break?
10] How can repair introduce insertions or deletions?
11] What can a supplied template support?
12] How does base editing differ from cutting both DNA strands?
13] Why do gene-function experiments need controls?
14] What cells does Casgevy edit?
15] How does its mechanism affect fetal haemoglobin?
16] Why is delivery a major challenge?
17] What must researchers assess in edited crops?
18] How do off-target and unexpected on-target changes differ?
19] How does somatic editing differ from heritable reproductive editing?
20] Why do consent, follow-up, and fair access matter?
Teaching illustrations and similes
1] DNA — A set of instructions influences activity; cells and environments also determine outcomes.
2] Mutation — A changed word can alter a message; many sequence changes have little effect.
3] Microbial defence — A record helps recognise returning intruders; bacteria have no conscious memory.
4] Guide RNA — A matching address directs a tool; similar sequences can cause mistakes.
5] Cas9 — Scissors make a break; they do not independently guarantee the desired repair.
6] Cell repair — A repair team may patch a damaged line differently; pathways have biological constraints.
7] Base editing — A targeted letter change differs from removing a passage; allowed changes are limited.
8] Controls — Comparing treated and untreated gardens helps identify causes; cell experiments need carefully matched groups.
9] Delivery — A useful tool must reach the correct workshop; biological barriers make that difficult.
10] Heritable change — Altering a master copy can affect later copies; inheritance and development are more complex than photocopying.
