Genetic Engineering

Essential Question

What are the benefits and risks of changing an organism’s DNA?

Scientists can move a gene from one organism to another and can even edit DNA directly. These tools already make medicines and change crops, and they raise questions that science alone cannot answer. In this lesson, you’ll learn how recombinant DNA is made, see some uses, and practice weighing benefits and risks with claim, evidence, reasoning.

Making Recombinant DNA

• Recombinant DNA combines DNA from two sources
• A restriction enzyme cuts the plasmid and the gene
• DNA ligase joins the gene into the plasmid
• Bacteria take in the plasmid (transformation), and antibiotic selects the cells that did

Genetic engineering is changing an organism’s DNA on purpose. One method makes recombinant DNA, which is DNA from two sources joined together. A plasmid is a small circle of DNA in a bacterium that is separate from its main chromosome. First, a restriction enzyme cuts the plasmid and also cuts the gene of interest from another organism. Second, the enzyme DNA ligase joins the gene into the plasmid. Third, bacteria take in the plasmid, which is called transformation. Last, the bacteria are placed on a plate with an antibiotic. The plasmid also carries a gene for antibiotic resistance, so only the bacteria that took in the plasmid can grow. This works across species because the genetic code is nearly the same in all organisms, so a bacterium can read a human gene and make the protein (see Translation, Unit 9). When these bacteria divide, they copy the plasmid and the gene it carries, so growing them makes many copies of the gene. Making many copies of a gene this way is called gene cloning. The word cloning is also used for making a whole organism with nearly the same nuclear DNA as a donor, which is a different process. Dolly the sheep was made this way, by placing the nucleus of an adult body cell into an egg cell whose own nucleus had been removed.

Uses of Genetic Engineering

• Medicine: bacteria can make human proteins such as insulin
• Agriculture: crops can make their own protection against pests
• Gene therapy: a patient’s own cells can be edited to treat a disease
• Each use has benefits and open questions

Use	What was changed	Purpose
Human insulin (approved 1982)	Bacteria were given the human insulin gene	A reliable supply of insulin for people with diabetes; before this, insulin came from the pancreases of cows and pigs
Bt corn	Corn was given a gene from a soil bacterium (Bacillus thuringiensis) for a protein that harms certain insect pests	Less crop damage, and in some cases less insecticide spraying
Casgevy (approved in 2023)	The patient’s own blood stem cells are edited with CRISPR, then returned	A treatment for sickle cell disease in people 12 and older; the edit is made in the patient’s blood cells, not in eggs or sperm

Bacteria with the human insulin gene were the basis for the first recombinant DNA medicine approved in the United States, in 1982. Bt crops make a protein from the bacterium Bacillus thuringiensis that is toxic to certain insects. An organism whose DNA has been changed by genetic engineering is often called a genetically modified organism (GMO), and Bt corn is an example. In December 2023, the U.S. FDA approved Casgevy, the first CRISPR-based treatment approved in the United States, for sickle cell disease in people 12 and older. The edit does not fix the sickle cell mutation itself. It lets the patient’s red blood cells make more fetal hemoglobin, which does not sickle. Many other applications are in research, so the list of uses keeps changing.

Claim, Evidence, Reasoning: Weighing Benefits and Risks

• Evidence is what can be measured or checked
• Reasoning links the evidence to a claim, and values affect how benefits and risks are weighed
• Different people can reach different claims from the same evidence
• A strong response uses accurate evidence and explains its reasoning

Use	Benefits people point to	Risks and concerns people raise
Insulin from bacteria	A reliable supply at large scale	Cost and access for patients
Bt corn	Less crop damage and, in some cases, less spraying	Pests can evolve resistance, so the EPA requires refuges of non-Bt plants; effects on other organisms need study
Gene therapy	A possible treatment for serious genetic diseases	Long-term effects are still being studied; very high cost and unequal access; questions about who decides when editing is appropriate

Perspective	What this person or group may weigh
A patient or family affected by a genetic disease	Access to a treatment, its cost, and its unknown long-term effects
A farmer	Crop losses, the cost of seed and spraying, and whether pests will become resistant
An environmental scientist	Effects on other organisms and on the ecosystem, and evidence from long-term monitoring
A government regulator	Safety evidence, rules for testing, and balancing public benefit and risk
A person focused on fairness or ethics	Who gets access, who controls the technology, and what changes to DNA are acceptable

Science can measure benefits and risks, for example how much a Bt crop reduces spraying or how quickly pests evolve resistance. Whether the benefits outweigh the risks also depends on values, such as how much weight a person gives to safety, cost, fairness, or the environment. To practice, choose one use from the table. Claim: state whether the benefits outweigh the risks, or what conditions would be needed. Evidence: give at least one accurate benefit and one accurate risk or concern, with numbers if you have them. Reasoning: explain how the evidence supports your claim, and say whose perspective you considered. Because people weigh values differently, claims on either side can be well supported. The table of perspectives shows some of the views people hold.

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Worked Examples

Try each problem on your own first, then open the solution to check your work.

Example 1: Size of a Recombinant Plasmid

A plasmid is cut with a restriction enzyme. The vector (the plasmid without the gene) is 3,000 bp. A gene of 1,200 bp is inserted. (a) What is the size of the recombinant plasmid? (b) After transformation, 150 colonies grow on an antibiotic plate from 0.05 micrograms (ug) of plasmid DNA. How many colonies per microgram of DNA is this?

Show the solution

1. (a) Add the pieces: The recombinant plasmid is the vector plus the insert: 3,000 bp + 1,200 bp = 4,200 bp.
2. (b) Colonies per microgram: Divide the number of colonies by the amount of DNA: 150 colonies / 0.05 ug = 3,000 colonies per ug.
3. Answer: (a) 4,200 bp. (b) 3,000 colonies per ug.

Example 2: Evidence from Data

The graph shows sample data (made up for practice) for the fraction of pests that are resistant to a Bt crop each year. In one set of fields all plants are Bt. In another set, some non-Bt plants (a refuge) are planted too. Write a claim, evidence, reasoning statement about planting refuges.

Show the solution

1. Claim: Planting a refuge slows the spread of resistance to the Bt crop.
2. Evidence: After 6 years, 81% of the pests were resistant with no refuge, compared with 11% with a refuge. In year 3 the values were 17% and 4%.
3. Reasoning: Where only Bt plants are grown, pests that survive the toxin are the only ones that reproduce, so resistance alleles become common quickly (natural selection, as in Unit 4). In a refuge, pests without resistance survive and mate with resistant pests, which keeps the resistance allele less common. These data are made up for practice, and they say nothing by themselves about whether Bt crops should be used.
4. Answer: Refuges slow resistance: 81% resistant with no refuge versus 11% with a refuge after 6 years.

Example 3: Evidence or Value Judgment?

Classify each statement as evidence or a value judgment, and explain.

Statement
(a) In the sample data, 81% of pests were resistant after 6 years with no refuge.
(b) Farmers should be required to plant refuges.
(c) The FDA approved Casgevy in December 2023 for sickle cell disease.
(d) It is wrong to change human DNA.

Show the solution

1. (a) Evidence: It is a measurement that can be checked.
2. (b) Value judgment: It says what people ought to do. Evidence about resistance can inform it, but it also depends on how people weigh costs, benefits, and fairness.
3. (c) Evidence: It is a fact that can be checked in official records.
4. (d) Value judgment: It expresses what a person believes is right or wrong. People hold different views on it, and the measurements alone do not settle it.
5. Answer: (a) Evidence. (b) Value judgment. (c) Evidence. (d) Value judgment.

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Practice

Practice naming the tools of recombinant DNA, calculating plasmid sizes and colony counts, writing a claim, evidence, reasoning statement, and separating evidence from value judgments. Try it on your own first, then check your work with the answer key.

• Genetic Engineering Practice Worksheet (PDF)
• Genetic Engineering Practice Answer Key (PDF)

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Lesson Slides

• 10.9 Genetic Engineering Slides (PDF)

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Big Ideas

• Recombinant DNA joins DNA from two sources
• Restriction enzymes cut, DNA ligase joins, and plasmids carry genes into bacteria
• Genetic engineering is used in medicine, agriculture, and gene therapy
• Evidence can be measured, and value judgments depend on what people care about
• Claims on either side can be well supported if the evidence and reasoning are strong

Back to the essential question: Changing an organism’s DNA can bring benefits, such as medicines and crop protection, and risks, such as resistance and cost or access. Science supplies the evidence, and people weigh it using their values, so different well-supported claims are possible. Next, you can return to the Biology course page to review other units.

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