Interpret original expression records without confusing RNA counts and gene absence
Invented equal-sample message counts: A E 6 C 2 R 0; B E 0 C 4 R 5. Both contain the same three supplied DNA genes. B has two more C messages and twice A’s count; detection is not gene presence or a protein-production rate.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Recall the nucleus, DNA base pairing, gametes, fertilisation, enzymes, membrane carriers and chemical synapses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
How many supplied DNA gene identities are in each sample?
What you will learn
- Compare expression in equally sampled model cells
- Keep DNA presence transcript detection and protein evidence separate
Original teaching model. Counts and records are stipulated; drawings are schematic.
| Feature | Meaning |
|---|---|
| Shared DNA identities | E, C and R in both samples |
| Sample A messages | E 6; C 2; R 0 |
| Sample B messages | E 0; C 4; R 5 |
| C comparison | B has 2 more and twice A’s count |
Compare expression in equally sampled model cells
An original model supplies two equal-sized samples of nucleated cells with the same three DNA genes E, C and R. The same detection method and sampling window are stipulated. Detected mRNA counts in sample A are E 6, C 2, R 0; in sample B they are E 0, C 4, R 5. These invented records practise interpretation rather than describe a real study or clinical range.
The DNA gene collection remains three identities in both samples despite different message counts. Sample A has detected E and C messages, while sample B has detected C and R messages. This is consistent with different expression of the supplied information. Counts of mRNA molecules are not counts of DNA genes or chromosome pairs.
Keep DNA presence transcript detection and protein evidence separate
A zero detected count in this window does not prove a gene is absent from DNA, especially when the DNA record explicitly says it is present. It also does not establish that a protein was never produced or that every pre-existing product has vanished. Detection timing and the supplied evidence category matter when comparing messages with proteins.
Compare the C counts using the stated equal sampling conditions: B has 4 − 2 = 2 more detected C messages and twice A’s count. This difference does not automatically measure a protein-production rate or a causal effect of a treatment because no such time-series or intervention record is supplied. The original table keeps information presence and measured message counts separate.
Sources for this lesson
Pause and explain
How does B’s C count compare with A’s under the stipulated equal sampling?
Worked example
Sample A has no R messages detected but the DNA record includes R. Is the R gene absent?
Show the worked solution
- Retain the given DNA gene presence.
- Identify zero as a detection result in the stated window.
Answer No. R is present in the supplied DNA record; zero detected messages in that window does not mean the gene is absent.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
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.
Identify the detected message categories in A (E 6, C 2, R 0) and B (E 0, C 4, R 5).
Give me a hint
Use positive detected counts without deleting supplied DNA genes.
Compare my reasoning
- Name E and C messages in A.
- Name C and R messages in B.
A has detected E and C messages; B has detected C and R messages. Both still have the same three supplied DNA gene identities.
Look for these in your work
- Use the message records
- Retain DNA presence
Calculate the absolute and multiplicative difference between C counts A 2 and B 4.
Give me a hint
Use subtraction and the A baseline.
Compare my reasoning
- Subtract 2 from 4.
- Divide 4 by 2.
B has two more detected C messages and twice A’s count under the stipulated equal sampling conditions.
Look for these in your work
- Give the absolute difference
- Give the ratio and conditions
A report says zero E messages in B prove the E gene and every earlier E protein are absent. Evaluate.
Give me a hint
The evidence categories and timing differ.
Compare my reasoning
- Retain E in the supplied DNA record.
- Reject absence of all earlier proteins from a message-window result.
Both claims are unsupported: E is present in the given DNA record, and zero detected messages in this window does not prove every earlier E protein is absent.
Look for these in your work
- Separate DNA and RNA evidence
- Retain the timing limit
Common mistakes
- mRNA counts are not counts of gene identities.
- Zero detection does not prove no previous protein production.
What can you explain now?
How does B’s C count compare with A’s under the stipulated equal sampling?
Compare with the explanation
Two more and twice the count
4 − 2 = 2 and 4/2 = 2.
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Make it stick
Explain compare expression in equally sampled model cells and keep DNA presence transcript detection and protein evidence separate. Use the stated cell, chromosome sets and information pathway before opening the solutions.
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.