Trace both chromosome sets through normal mitosis
In the stipulated n = 3 diploid model, both daughters receive types 1, 2 and 3 from both set contributions: two sets, three pairs and six individuals per daughter.
Section 17.2 · Mitosis
Exam scope and assessment notes
Extended only (Supplement) · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall chromosomes, genes, chromosome sets, selective gene expression and the distinction between a nucleus and a whole cell.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
A diploid n = 3 parent divides by normal mitosis. What is in each daughter?
What you will learn
- Maintain the diploid complement
- Distinguish sets pairs and individual counts
Original teaching model. Counts and records are stipulated; drawings are schematic.
| Feature | Meaning |
|---|---|
| Parent model | n = 3; two sets; six chromosomes |
| After copying | Six replicated chromosomes; twelve DNA molecules |
| Each completed daughter | Two sets; three pairs; six chromosomes |
| Both daughters combined | Twelve chromosomes across two separate nuclei |
Maintain the diploid complement
A diploid nucleus contains two chromosome sets. Normal mitosis preserves both sets in each daughter rather than putting one set into each product. In the original n = 3 model, each set has types one, two and three, giving six individual chromosomes in three corresponding pairs. After accurate replication and separation, each daughter retains both sets and all six chromosomes.
The parent model labels the contributions as 1A, 2A, 3A and 1B, 2B, 3B, where A and B label the two set contributions rather than allele dominance. Each individual chromosome is copied. Both daughters receive all six labels. Replication therefore prepares two copies of the whole diploid complement; it does not change the completed products to one-set gametes.
Distinguish sets pairs and individual counts
The attached-copy preparation stage has six replicated chromosomes and twelve DNA molecules under the stated counting rule. Each completed daughter has six individual chromosomes and six DNA molecules in this unreplicated endpoint model. Across the two daughters there are twelve chromosomes, but each nucleus still has two sets rather than four.
A chromosome set is an information grouping, not one long chromosome object. Keep the unit visible when calculating: three types in each set times two sets gives six individuals. Neither three pairs nor six copies by itself tells you the full relationship unless the labels and stage are supplied. This distinction prevents a halving explanation from being accidentally called mitosis.
Pause and explain
What does the set label A mean in the supplied 1A 2A 3A record?
Worked example
The n = 3 parent is diploid. Count each completed mitotic daughter.
Show the worked solution
- Use two sets of three types.
- Give both sets to each daughter.
Answer Each daughter is diploid with six chromosomes in three corresponding pairs.
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.
Calculate the individual count for two sets with three chromosome types in each.
Give me a hint
Multiply types per set by sets.
Compare my reasoning
- Use three individuals per set.
- Calculate three times two.
The diploid model contains six individual chromosomes in three corresponding pairs.
Look for these in your work
- Show the set multiplication
- Label individuals and pairs
Trace 1A 2A 3A 1B 2B 3B into both daughters after normal accurate mitosis.
Give me a hint
Preserve every original label.
Compare my reasoning
- Copy each individual chromosome.
- Distribute one copy of all six to each product.
Each daughter receives 1A, 2A, 3A, 1B, 2B and 3B, maintaining two sets and six chromosomes.
Look for these in your work
- Include both sets
- Maintain the per-daughter count
A drawing assigns set A only to one daughter and set B only to the other. Explain why that does not show normal mitosis for this diploid parent.
Give me a hint
Check the complete complement in each daughter.
Compare my reasoning
- Identify one set in each shown product.
- Compare with the original two-set nucleus.
Each shown product has only one set and three chromosomes, so it halves the parent complement instead of maintaining both sets in each daughter.
Look for these in your work
- Identify the halving
- Explain the missing complement
Common mistakes
- Mitosis preserves both sets in each diploid daughter.
- Sets, pairs and individual chromosomes are different units.
What can you explain now?
What does the set label A mean in the supplied 1A 2A 3A record?
Compare with the explanation
One named set contribution
The model explicitly defines this label.
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Make it stick
Without your notes, maintain the diploid complement and distinguish sets pairs and individual counts. Distinguish nuclear division, chromosome copies and completed daughter cells 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.