TCE Biology — Level 3
Meiosis — TCE Biology — Level 3 Flashcards & Quiz
Meiosis is a specialised form of cell division that produces haploid gametes from diploid parent cells. TCE Biology Level 3 expects you to describe the two sequential divisions, explain how crossing over and independent assortment generate genetic variation, and compare meiosis with mitosis. Non-disjunction errors and their consequences (e.g. Down syndrome) are standard application content.
Key Points
- Meiosis is a reduction division: one diploid cell (2n) produces four haploid cells (n).
- Meiosis I separates homologous chromosome pairs (reduction step); meiosis II separates sister chromatids (like mitosis).
- Crossing over in prophase I exchanges segments between homologous chromosomes at chiasmata, creating new allele combinations.
- Independent assortment in metaphase I: homologous pairs align randomly, giving 2ⁿ possible chromosome combinations (n = haploid number).
- Random fertilisation adds further variation: any sperm can meet any egg.
- Non-disjunction errors (failure to separate) cause aneuploidy — e.g. trisomy 21 (Down syndrome).
Common Mistakes to Avoid
- Stating meiosis produces two haploid cells — it produces FOUR.
- Forgetting crossing over happens in prophase I, not II.
- Confusing independent assortment (different genes) with crossing over (same gene, different alleles).
- Mixing up haploid and diploid when labelling diagrams.
- Missing one of the three sources of variation (crossing over, independent assortment, random fertilisation).
Exam Strategy
TASC Level 3 meiosis questions usually ask you to compare meiosis with mitosis or explain how meiosis generates variation. Structure: (1) state purpose (gamete production vs growth/repair), (2) outline the two divisions, (3) name all three sources of variation with mechanisms, (4) link to evolution and natural selection. Diagrams with labelled stages strengthen responses.
Sample Flashcards
Q1: How does crossing over during meiosis increase genetic variation?
In prophase I, homologous chromosomes pair up. Non-sister chromatids of the homologous pair exchange equivalent sections of DNA at points called chiasmata. This recombination produces chromatids with new combinations of alleles that were not present on either parental chromosome, so each gamete is genetically different.
Q2: How do independent assortment and random fertilisation increase genetic variation?
Independent assortment: in metaphase I, each homologous pair lines up at the equator independently of the other pairs, so the maternal and paternal chromosomes are sorted into gametes in many different combinations (2ⁿ, where n is the haploid number). Random fertilisation: any sperm can fertilise any egg, multiplying the possible combinations again.
Sample Quiz Questions
Q1: Crossing over occurs between non-sister chromatids of homologous chromosomes during prophase I.
Answer: TRUE
Exchange of DNA between non-sister chromatids produces new combinations of alleles.
Q2: Independent assortment occurs because homologous pairs line up randomly at the equator in metaphase I.
Answer: TRUE
The random orientation of each pair sorts maternal and paternal chromosomes into gametes in many combinations.
Revision Tip
The mitosis/meiosis comparison is high-yield — drill a Revizi flashcard deck with rows for purpose, divisions, daughter cells, ploidy, variation, and genetic outcome.
Related Concepts
Last updated: 9 October 2026 · 2 sample flashcards · 2 sample quiz questions