Trace chromosome behaviour through meiosis
Describe the main chromosome, spindle, nuclear-envelope and cell-surface events in meiosis I and II.
A Level; Cambridge International Biology 9700, 2028–2030. Written answers are self-checked; this is not practical-skills certification.
Before you begin
- Genes are DNA sequences that can be inherited; meiosis and fertilisation link parental genomes.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What separates at anaphase II?
What you will learn
- Describe the main stages of meiosis I and meiosis II
- Relate spindle attachment, chromosome movement, nuclear envelopes and cytokinesis to each division
Original teaching model. Counts, source combinations and sample records are stipulated; drawings are schematic.
| Feature | Meaning |
|---|---|
| Normal diploid mitosis | 6 → 6 in each daughter; maintained complement |
| Normal meiotic reduction | 6 → 3 in each final product; one complete set |
| Normal fertilisation | 3 + 3 → 6 in the zygote nucleus |
| Evidence limit | Six alone does not establish which event occurred |
Build the genetic explanation
In prophase I, homologous chromosomes pair; the nuclear envelope breaks down and a spindle forms. At metaphase I, homologous pairs align at the equator. In anaphase I, homologues move to opposite poles while centromeres remain intact and sister chromatids stay together. Telophase I may reform nuclear envelopes and cell division produces two haploid nuclei with replicated chromosomes. In prophase II a new spindle forms; chromosomes align singly at metaphase II; centromeres divide and sister chromatids separate at anaphase II; and telophase II reforms nuclei. Cytokinesis produces four haploid nuclei.
Check the evidence and limits
The syllabus expects the eight main stages but not subdivisions of prophase I. In plant cells, cytokinesis forms a cell plate; in animal cells, the surface membrane constricts. Do not separate sister chromatids in anaphase I.
Pause and explain
A plant meiosis diagram shows a plate forming across the cell at the end of a division. Explain the structure and stage context.
Worked example
At anaphase I, which structures move apart and which remain joined?
Show the worked solution
- Homologous chromosomes separate.
- Centromeres do not divide until meiosis II.
Answer Homologous chromosomes move to opposite poles; sister chromatids remain joined at their centromeres.
Try a topic test
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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.
Compare chromosome movement at anaphase I and anaphase II.
Give me a hint
Set out the alleles or steps before deciding the outcome.
Compare my reasoning
- Homologues separate in meiosis I.
- Centromeres divide and sister chromatids separate in meiosis II.
At anaphase I homologous chromosomes move apart while sister chromatids remain attached. At anaphase II centromeres divide and sister chromatids separate.
Look for these in your work
- Genetic terms used correctly
- Steps linked
A stage shows homologous pairs lined up at the equator with spindle fibres attached. Identify the stage and one event that follows.
Give me a hint
Use the given evidence and state your assumptions.
Compare my reasoning
- Pairs, not single chromosomes, align in meiosis I.
- Homologues separate next.
It is metaphase I. In anaphase I, homologous chromosomes move to opposite poles.
Look for these in your work
- Prediction or interpretation supported
- Limits stated
A plant meiosis diagram shows a plate forming across the cell at the end of a division. Explain the structure and stage context.
Give me a hint
Apply the inheritance or gene-control model to the new context.
Compare my reasoning
- The cell plate forms during cytokinesis in plant cells.
- It separates daughter cytoplasm after nuclear division.
The cell plate forms during cytokinesis in a plant cell, partitioning the cytoplasm after a meiotic nuclear division.
Look for these in your work
- Model applied accurately
- Unsupported certainty avoided
Common mistakes
- Separating sister chromatids in meiosis I
- Describing anaphase II as separation of homologues
What can you explain now?
What separates at anaphase II?
Compare with the explanation
Sister chromatids
Centromeres divide and sister chromatids move to opposite poles.
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Make it stick
What separates in meiosis I, and what separates in meiosis II?
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.