Explain meiosis as a source of genetic variation through different gamete combinations
Different combinations preserve complete haploid sets in the supplied model.
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 genes, alleles, genotype and phenotype from the inheritance pathway. Use the stated organism, units and sample; the records in these lessons are invented.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Can two complete haploid gametes differ genetically?
What you will learn
- Connect meiosis with genetically varied gametes
- Keep source combinations separate from new alleles and chromosome counts
Original teaching model. Measurements, categories, DNA fragments and comparison records are invented; assumptions and sample boundaries are stated.
| Feature | Meaning |
|---|---|
| Possible sources | A or B for each chromosome type |
| Combinations | AA / AB / BA / BB |
| Within one gamete | One each of types 1 and 2: n = 2 |
| Not implied | Every event gives all four; source labels show new alleles |
Connect meiosis with genetically varied gametes
Meiosis is one required source of genetic variation in populations. It produces haploid cells with reduced chromosome sets and can produce different combinations of inherited information. This lesson connects the preceding Meiosis pathway with variation: a cell can contain one complete chromosome set while carrying a combination different from another gamete. Set completeness and genetic identity are different questions.
The original simplified model has two chromosome types, labelled one and two, with source A or source B copies of each in the diploid precursor. Across repeated events, the supplied independent source-choice model permits combinations AA, AB, BA and BB. The first letter names the source of chromosome type one and the second the source of type two. The letters are source labels, not dominant and recessive allele symbols.
Keep source combinations separate from new alleles and chromosome counts
Each displayed valid gamete has one chromosome of type one and one of type two, so its haploid count is two; the normal diploid precursor count is four. Four possible source combinations are not four chromosomes in each gamete. The model also does not require every single meiotic event to produce all four source combinations or every finite sample to contain equal numbers of them.
The stated no-exchange source model reshuffles inherited copies without changing the tracked allele sequences. Mutation is a separate source that can form new allele versions. Meiosis can involve further processes not drawn by this simple source key, but naming their detailed stages is not needed for this requirement. State the model and avoid treating a colour or source label as a measured DNA sequence or a phenotype guarantee.
Pause and explain
What does AA mean in the supplied two-type source key?
Worked example
Enumerate source combinations for two chromosome types with A/B choices, then distinguish them from gamete chromosome count.
Show the worked solution
- Choose A or B for type one and A or B for type two to obtain AA, AB, BA and BB.
- Each combination contains one copy of each type, so n = 2 and the stipulated precursor has 2n = 4.
Answer Four possible source combinations; two chromosomes per complete haploid gamete in this model. Not every one event or finite sample is guaranteed to show all four.
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.
List all two-type A/B source combinations under the stated independent model.
Give me a hint
Choose each source for the first type, then the second.
Compare my reasoning
- For first source A, second source A or B gives AA or AB.
- For first source B, second source A or B gives BA or BB.
AA, AB, BA and BB: four possible source combinations across the supplied model.
Look for these in your work
- All four combinations
- Not guaranteed products of one event
Each gamete contains one chromosome of each of two types. Find n, the normal 2n precursor count and the distinction from four possible combinations.
Give me a hint
Count chromosome identities within one gamete, not outcomes across events.
Compare my reasoning
- One of each two types means n = 2.
- Two full precursor sets mean 2n = 4.
n = 2 per gamete and 2n = 4 in the precursor. Four possible source combinations are a different count.
Look for these in your work
- Correct n and 2n
- Outcome count distinguished
Five sampled gametes all show source combination AB. Does that prove meiosis cannot produce genetically different gametes or that a new allele arose?
Give me a hint
A small source-label sample lacks sequence-origin evidence.
Compare my reasoning
- The sample does not have to contain every possible model combination.
- AB source labels do not show an altered internal allele sequence.
Neither follows. The sample lacks other recorded combinations but does not rule them out, and source labels alone do not establish new allele formation.
Look for these in your work
- Finite-sample limit
- Combination versus allele-origin evidence
Common mistakes
- Using four possible combinations as chromosome count
- Treating source labels as dominance symbols
- Requiring every event or sample to show all possibilities
What can you explain now?
What does AA mean in the supplied two-type source key?
Compare with the explanation
A-source copies of chromosome types one and two
The two positions correspond to distinct chromosome types.
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Make it stick
Without your notes, connect meiosis with genetically varied gametes and keep source combinations separate from new alleles and chromosome counts. Keep units, the stated sample and the limits of the evidence clear.
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.