Key Learning Objectives
- Explain why gametes must contain half the diploid chromosome count (haploid).
- Describe the two division cycles in meiosis resulting in four unique daughter cells.
- Compare mitosis and meiosis across cell counts, chromosome numbers, and genetic variation.
Topic Summary & Core Notes
Discover how reproductive organs produce non-identical haploid gametes (sperm, egg, pollen) via two rounds of nuclear division.
Key Rules, Formulas & Definitions
Meiosis Rule
1 Diploid Parent Cell (2n) → 4 Genetically Unique Haploid Gametes (n)
2 Step-by-Step Worked Examples
Worked Example 1
Worked Example 1: Calculating Gamete Chromosomes
Question: A dog body cell has 78 chromosomes. How many are in a dog sperm cell?
Step-by-Step Solution:
- Step 1: Gamete rule: Gametes are haploid (half the diploid number).
- Step 2: Calculate: 78 ÷ 2 = 39.
Final Answer: 39 chromosomes
Senior Examiner Insight: Gametes are always haploid.
Worked Example 2
Worked Example 2: Fertilisation Restoration
Question: Why must gametes be haploid rather than diploid?
Step-by-Step Solution:
- Step 1: Fusion: At fertilisation, two gametes fuse: n + n = 2n.
- Step 2: Stability: If gametes were diploid (2n), chromosome numbers would double every generation.
Final Answer: To maintain a constant chromosome number from generation to generation after fertilisation.
Senior Examiner Insight: State that fertilisation restores the diploid number.
Common Pitfalls & Examiner Warnings
Common Mistake: Confusing Mitosis and Meiosis
Mitosis makes 2 identical diploid cells; Meiosis makes 4 unique haploid gametes.
Interactive Self-Check Quiz (3 Questions)
Question 1 of 3
How many daughter cells result from meiosis?
Click to Reveal Answer & Mark Scheme
Correct Answer: C) 4
Detailed Explanation: Meiosis produces 4 haploid gametes.
Mark Scheme & Scoring Points: 1 mark for 4.
Question 2 of 3
Where does meiosis occur in humans?
Click to Reveal Answer & Mark Scheme
Correct Answer: A) Testes and ovaries
Detailed Explanation: Meiosis occurs exclusively in reproductive organs to form gametes.
Mark Scheme & Scoring Points: 1 mark for Testes and ovaries.
Question 3 of 3
What term describes cells containing a single set of chromosomes?
Click to Reveal Answer & Mark Scheme
Correct Answer: A) Haploid
Detailed Explanation: Haploid cells contain one complete set of chromosomes (n).
Mark Scheme & Scoring Points: 1 mark for Haploid.
Created by Fiaraz Iqbal
Former Headteacher & Senior Science / Maths Examiner
Fiaraz produces structured video walkthroughs, Tier 3 literacy packs, and exam mark scheme breakdowns to help secondary students achieve top grades.
Accelerate Your Academic Progress
Join tailored 1-to-1 or masterclass revision programmes with senior examiner insights.
Book a Free Consultation