Cell Division, Reproduction & Development — Extension · Life Science: Biology, Grade 10
Connect chromosome continuity, variation, regulated growth, and specialization.
Model Chromosome Continuity and Variation
Investigate
How do division models preserve chromosome number or reduce it?
Use three sessions: define question, boundary, model and route; collect or analyze the supplied repeated records; then graph, explain, revise and submit the notebook. Home-study activities do not certify NYSED laboratory minutes or mandated investigations.
Materials
- Paper chromosome strips labeled A/a and B/b
- Pencil
- Supplied comparison table
Before you begin
Use the supplied paper-and-data model. This activity requires no biological samples, cultures, personal health information, or tests on people.
Plan a fair test
Use a simple organism with 2n = 4 and two chromosome pairs. Each replicated chromosome has two chromatids; chromosomes are counted by centromeres, not by the number of drawn strands. The model ignores detailed DNA sequences.
Method
- Build a starting diploid cell with two homologous pairs.
- Duplicate each chromosome to model DNA replication; count chromosomes and chromatids separately.
- Model mitosis and distribute copies to two daughters.
- Rebuild the replicated cell and model meiosis I, then meiosis II.
- List possible A/B allele combinations in gametes, assuming the genes are on different chromosomes.
- Model fertilization and explain how diploid number is restored.
Open the investigation data (illustrative)
Illustrative data authored for this activity, not an actual experiment or an official mandated investigation. Use them as supplied evidence, not as your own observations.
| Stage | Chromosomes per cell | Chromatids per cell |
|---|---|---|
| Before replication | 4 | 4 |
| After replication, before division | 4 | 8 |
| Each normal mitotic daughter | 4 | 4 |
| Each cell after meiosis I | 2 | 4 |
| Each gamete after meiosis II | 2 | 2 |
Analyze and explain
- Why does DNA replication not double chromosome number under this convention?
- Compare the outcomes of mitosis and meiosis.
- Identify two sources of variation omitted or simplified in the paper model.
- Separate collected measurements from the supplied illustrative records.
- Explain how labeled mechanisms constrain the pattern rather than only restate the graph.
- Propose a further comparison that could distinguish an alternative explanation.
What a strong explanation includes
- Counts centromeres and chromatids consistently
- Separates homologous chromosomes in meiosis I and chromatids in meiosis II
- Connects fertilization with number restoration
- States model limits and sources of variation
- State units, boundary, comparable conditions and model assumptions.
- Retain a first explanation and an evidence-supported revision.
Parent / teacher guide: discuss after the investigation
Replication doubles chromatids while each joined pair is still counted as one chromosome. Normal mitosis produces daughters with four chromosomes; meiosis produces gametes with two. Fertilization combines two haploid sets to restore four. Independent assortment, crossing over, and which gametes combine contribute to variation; the strips simplify crossover and omit nucleotide-level mutation. A complete response also states the system boundary, units, matched conditions and limitations. Distinguish supplied illustrative outcomes from collected measurements, and explain why your revised mechanism fits the relevant evidence. Different observations should be interpreted rather than replaced to match the example.
Compare this model with the learner’s actual evidence. Different measurements can support a different conclusion; check the reasoning and limitations, not matching wording.
Extend the chapter investigation by evaluating its evidence and proposing a better test.
Problem 1
Answer and explanation
Replication doubles chromatids while each joined pair is still counted as one chromosome. Normal mitosis produces daughters with four chromosomes; meiosis produces gametes with two. Fertilization combines two haploid sets to restore four. Independent assortment, crossing over, and which gametes combine contribute to variation; the strips simplify crossover and omit nucleotide-level mutation. A complete response also states the system boundary, units, matched conditions and limitations. Distinguish supplied illustrative outcomes from collected measurements, and explain why your revised mechanism fits the relevant evidence. Different observations should be interpreted rather than replaced to match the example.
Problem 2
Answer and explanation
Replication doubles chromatids while each joined pair is still counted as one chromosome. Normal mitosis produces daughters with four chromosomes; meiosis produces gametes with two. Fertilization combines two haploid sets to restore four. Independent assortment, crossing over, and which gametes combine contribute to variation; the strips simplify crossover and omit nucleotide-level mutation. A complete response also states the system boundary, units, matched conditions and limitations. Distinguish supplied illustrative outcomes from collected measurements, and explain why your revised mechanism fits the relevant evidence. Different observations should be interpreted rather than replaced to match the example.
Problem 3
Answer and explanation
Replication doubles chromatids while each joined pair is still counted as one chromosome. Normal mitosis produces daughters with four chromosomes; meiosis produces gametes with two. Fertilization combines two haploid sets to restore four. Independent assortment, crossing over, and which gametes combine contribute to variation; the strips simplify crossover and omit nucleotide-level mutation. A complete response also states the system boundary, units, matched conditions and limitations. Distinguish supplied illustrative outcomes from collected measurements, and explain why your revised mechanism fits the relevant evidence. Different observations should be interpreted rather than replaced to match the example.
Problem 4
Answer and explanation
Replication doubles chromatids while each joined pair is still counted as one chromosome. Normal mitosis produces daughters with four chromosomes; meiosis produces gametes with two. Fertilization combines two haploid sets to restore four. Independent assortment, crossing over, and which gametes combine contribute to variation; the strips simplify crossover and omit nucleotide-level mutation. A complete response also states the system boundary, units, matched conditions and limitations. Distinguish supplied illustrative outcomes from collected measurements, and explain why your revised mechanism fits the relevant evidence. Different observations should be interpreted rather than replaced to match the example.
Problem 5
Answer and explanation
Replication doubles chromatids while each joined pair is still counted as one chromosome. Normal mitosis produces daughters with four chromosomes; meiosis produces gametes with two. Fertilization combines two haploid sets to restore four. Independent assortment, crossing over, and which gametes combine contribute to variation; the strips simplify crossover and omit nucleotide-level mutation. A complete response also states the system boundary, units, matched conditions and limitations. Distinguish supplied illustrative outcomes from collected measurements, and explain why your revised mechanism fits the relevant evidence. Different observations should be interpreted rather than replaced to match the example.
Problem 6
Answer and explanation
Replication doubles chromatids while each joined pair is still counted as one chromosome. Normal mitosis produces daughters with four chromosomes; meiosis produces gametes with two. Fertilization combines two haploid sets to restore four. Independent assortment, crossing over, and which gametes combine contribute to variation; the strips simplify crossover and omit nucleotide-level mutation. A complete response also states the system boundary, units, matched conditions and limitations. Distinguish supplied illustrative outcomes from collected measurements, and explain why your revised mechanism fits the relevant evidence. Different observations should be interpreted rather than replaced to match the example.