Genetic modification means taking a gene from one organism and inserting it into another so the recipient makes a useful protein or gains a useful feature. The exam asks you to outline the stages and explain why each is needed. It does not ask for a laboratory method.
This lesson builds on cell division and inheritance, because you need to know that a gene carries the instructions for one protein.
What is the idea in plain language?
A gene is a section of DNA that carries the instructions for making a protein. Every organism reads those instructions in the same basic way, so a bacterial cell can follow a human gene and make the human protein.
Genetic modification uses that fact. You find the useful gene, move it, and let the recipient’s cells do the rest.
What are the stages?
The classic example is bacteria that make human insulin, a protein that people with some types of diabetes need. The stages are:
| Stage | What happens | Why |
|---|---|---|
| 1. Identify | The human insulin gene is located | You need the exact instructions |
| 2. Cut | An enzyme (restriction enzyme) cuts the gene out, and also opens a bacterial plasmid | Enzymes cut DNA at specific places |
| 3. Join | Another enzyme (ligase) joins the gene into the plasmid | The plasmid now carries the gene |
| 4. Transfer | The plasmid is put into bacterial cells | Bacteria are the new host |
| 5. Grow | The bacteria are grown in large numbers | Each divides and copies the gene |
| 6. Collect | Insulin is made by the bacteria, then separated and purified | The product is what is useful |
A plasmid is a small ring of DNA found in bacteria. Here it acts as a vector, meaning a carrier that delivers the gene.
Worked example
Question: A scientist wants bacteria to make a human protein called protein X. Outline how this is done and explain why bacteria are suitable.
Step 1, name the target. The human gene for protein X is identified.
Step 2, cut and join. It is cut out with a restriction enzyme and joined into a plasmid with ligase.
Step 3, transfer and grow. The plasmid is taken up by bacterial cells, which are grown in large numbers.
Step 4, expression. The bacteria read the gene and make protein X, which is collected.
Step 5, explain suitability. Bacteria reproduce quickly, so there are many copies of the gene and a fast supply of protein. They are small and easy to grow in a controlled container, and they can read human genes because the genetic code is shared.
The mistake to watch for
Mistaken answer: “The bacteria were given insulin, so they can make more.”
This confuses the gene with the product. The bacteria were given the gene for insulin, and their own ribosomes then build the protein using that gene’s instructions.
The correction is to write the chain “gene → instructions → protein made by the host”. Check that the word “gene” appears where the DNA is moved. Check that “protein” appears where the product is made.
Check yourself
1. Give the role of a restriction enzyme and of ligase in the outline above.
Show answer
A restriction enzyme cuts DNA at a specific place (to remove the gene and open the plasmid). Ligase joins the gene into the plasmid.
2. Why is the plasmid called a vector?
Show answer
It carries the gene into the bacterial cell, so it acts as a carrier.
3. A student writes “the human insulin was injected into the bacteria”. Correct the sentence.
Show answer
The gene for human insulin was inserted into the bacteria, which then made the insulin protein.
Where this leads next
Compare this method with traditional breeding in distinguishing gene insertion from selective breeding, and test the ideas with the inheritance model board on a fictional allele. Earlier in the module, fermentation shows large-scale growth of microorganisms.
If outlines still come out jumbled, online one-to-one Biology tuition gives you a teacher who reads your draft with you and marks where the chain breaks.