Confirm expression with fluorescent marker genes
Explain how marker genes provide evidence that a transferred gene is expressed.
Section 19.1 · Principles of genetic technology
A Level; Cambridge International Biology 9700, 2028–2030. This is curriculum teaching, not medical advice or a claim that a treatment is suitable for an individual. Written responses are self-checked
Before you begin
- DNA stores genetic information; genes can be expressed to produce RNA and protein.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What can a fluorescent marker indicate?
What you will learn
- Explain how fluorescent marker genes can indicate gene expression
- Distinguish marker expression from proof of every intended outcome
Build the explanation
A marker gene may code for a fluorescent product. If the marker is transferred with a construct and is expressed, fluorescence provides evidence that genetic material entered a cell and the marker gene was expressed. A marker can help identify transformed cells or track expression.
Use the evidence carefully
Fluorescence is evidence about the marker, not automatic proof that every linked gene is intact, expressed at the needed level or produces a useful phenotype. Controls help distinguish true expression from background signal.
Pause and explain
What control could help determine whether a fluorescence signal is due to the marker?
Worked example
A cell fluoresces after receiving a construct with a fluorescent marker. What does the result support?
Show the worked solution
- The marker product is detected.
- This supports marker-gene expression.
Answer The fluorescence supports expression of the marker gene; additional evidence is needed to confirm expression or function of a separate target gene.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Why can fluorescence help identify transformed cells?
Give me a hint
Identify the relevant material or technology and explain each step.
Compare my reasoning
- Only cells expressing the marker produce the signal.
- The signal can be detected.
Fluorescence can identify cells in which the marker gene is expressed, helping select cells that received and expressed the construct.
Look for these in your work
- Method identified
- Steps linked to function
A marker fluoresces but the target protein is not detected. What does this show?
Give me a hint
Use the stated example to justify a conclusion.
Compare my reasoning
- Marker expression occurred.
- Target expression has not been established.
It shows the marker is expressed, but it does not establish that the target gene produced a detectable protein.
Look for these in your work
- Evidence interpreted
- Limits stated
What control could help determine whether a fluorescence signal is due to the marker?
Give me a hint
Apply the idea to a new application or trade-off.
Compare my reasoning
- Use a cell or sample without the marker construct.
- Compare background fluorescence.
A marker-free or otherwise suitable negative control estimates background fluorescence for comparison.
Look for these in your work
- Application explained
- Claim appropriately bounded
Common mistakes
- Saying fluorescence proves the organism is safe
- Assuming a marker measures the target protein directly
What can you explain now?
What can a fluorescent marker indicate?
Compare with the explanation
Expression of the marker gene
It does not prove every intended trait or effect.
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Make it stick
What can a fluorescent marker show, and what does it not guarantee?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.