Calculate chromosome counts from stipulated diploid models
Use set counts without assuming cross-species compatibility.
Extended only (Supplement); Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Recall DNA, inherited characteristics, nuclei and the distinction between growth and reproduction.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Model B has a diploid count of eighteen. What is its stipulated gamete count?
What you will learn
- Calculate n and 2n consistently
- Keep counts separate from DNA copying and compatibility
Calculate chromosome counts from stipulated diploid models
Stipulated diploid counts A 12, B 18, C 24 give compatible haploid counts 6, 9, 12. Count sums do not establish cross-species compatibility. Original teaching model.
| Model | Diploid (2n) | Haploid (n) |
|---|---|---|
| Model A | 12 | 6 |
| Model B | 18 | 9 |
| Model C | 24 | 12 |
| Feature | Meaning |
|---|---|
| Model A | 2n = 12; n = 6 |
| Model B | 2n = 18; n = 9 |
| Model C | 2n = 24; n = 12 |
| Limit | Stipulated counts, not measured species or viability evidence |
Calculate n and 2n consistently
The invented table gives diploid counts of twelve, eighteen and twenty-four for model organisms A, B and C. In the stipulated ordinary diploid model, the compatible gamete count is half of the diploid count: six, nine and twelve. Calculate within each organism, rather than using the same number for every species or interpreting n as the number of nuclei.
Compatible gamete nuclei of A contribute six plus six chromosomes to form a twelve-chromosome diploid zygote nucleus. For C, twelve plus twelve gives twenty-four. These sums restore the supplied two-set count. Showing the contribution sum explains the result better than writing a number with no statement of whether it describes a gamete or the zygote.
Keep counts separate from DNA copying and compatibility
Later DNA copying before a cell division is a different event from adding a new gamete contribution. Copying genetic material does not by itself establish another fertilisation or another complete contributor set. The lesson does not require a detailed chromatids account; use the initial fusion record for the zygote count and avoid silently doubling that answer because growth follows.
If a question combines gametes from different unspecified organisms, adding their counts alone does not prove compatibility, a viable zygote or an ordinary diploid outcome. Chromosome number is one part of a reproductive record, not a universal permission for any two gametes to fuse successfully. The table is a stipulated teaching model, not measured species data or a clinical interpretation.
Pause and explain
Does adding two gamete counts prove a viable cross between any organisms?
Worked example
An ordinary diploid model has 2n = 10. Find a compatible gamete count and the zygote count.
Show the worked solution
- Half of ten is five per gamete.
- Five plus five restores ten in the zygote.
Answer Gamete n = 5; zygote 2n = 10.
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.
Find the gamete chromosome count for model A with diploid count twelve.
Give me a hint
Calculate one of its two sets.
Compare my reasoning
- Two sets contain twelve.
- One set contains half that count.
Six chromosomes in a compatible haploid gamete nucleus.
Look for these in your work
- Halve the diploid count
- Name the gamete nucleus
Two compatible model C gamete nuclei each contribute twelve chromosomes. Find the initial zygote count and ploidy.
Give me a hint
Combine both complete sets.
Compare my reasoning
- Twelve plus twelve is twenty-four.
- Two sets mean diploid.
Twenty-four chromosomes in the diploid zygote nucleus.
Look for these in your work
- Add both contributions
- State diploid
An unfamiliar record adds a six-chromosome gamete to a nine-chromosome gamete from unspecified organisms. Does fifteen prove a viable ordinary diploid zygote?
Give me a hint
A numerical sum is not a compatibility test.
Compare my reasoning
- The counts sum to fifteen.
- Compatibility and corresponding complete sets are not established.
No. The sum is fifteen, but the record does not establish compatibility, a viable zygote or an ordinary diploid chromosome arrangement.
Look for these in your work
- Calculate the sum
- Keep biological evidence separate
Common mistakes
- Halving a count without naming the resulting stage.
- Using a sum to prove compatibility across unspecified organisms.
What can you explain now?
Does adding two gamete counts prove a viable cross between any organisms?
Compare with the explanation
No; compatibility and development need separate evidence
A sum alone is insufficient.
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Make it stick
Calculate gamete and zygote counts and explain why arithmetic alone cannot prove compatibility.
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.