IB MYP 4-5 Biology-Meiosis- Study Notes - New Syllabus
IB MYP 4-5 Biology-Meiosis- Study Notes – New syllabus
IB MYP 4-5 Biology-Meiosis- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Production of gametes
- Genetic variation through crossing over
- Comparison with mitosis
Production of Gametes
What Are Gametes?
Gametes are sex cells used in reproduction.
- In males, the gamete is the sperm
- In females, it is the egg (ovum)
Each gamete carries only half the number of chromosomes (haploid), so when they join (fertilization), the full set is restored in the new organism.
How Are Gametes Made?
Gametes are made through a special type of cell division called meiosis, which only happens in the testes (males) and ovaries (females).
Process: Meiosis – The Cell Division for Gametes
Meiosis turns one cell into four unique gametes, each with half the number of chromosomes.
Meiosis Happens in Two Main Stages:
- Meiosis I – Reduces chromosome number (from diploid to haploid)
- Meiosis II – Similar to mitosis, but divides the chromatids
Key Features:
- DNA is copied once, but the cell divides twice
- Produces 4 non-identical haploid cells
- Increases genetic variation among offspring
In Males: Sperm Production (Spermatogenesis)
| Feature | Details |
|---|---|
| Location | Testes |
| Process starts at | Puberty |
| Each cell makes | 4 functional sperm |
| Special features | Tail for swimming, lots of mitochondria for energy |
In Females: Egg Production (Oogenesis)
| Feature | Details |
|---|---|
| Location | Ovaries |
| Process starts at | Before birth (paused until puberty) |
| Each cell makes | 1 large egg + 3 small polar bodies |
| Special features | Big cytoplasm to support early embryo |
Why Is Gamete Production Important?
- Allows sexual reproduction
- Combines genes from two parents → genetic diversity
- Keeps chromosome number constant across generations
- Leads to variation, which is essential for evolution and survival
Summary Table – Production of Gametes
| Feature | Sperm (Male) | Egg (Female) |
|---|---|---|
| Location | Testes | Ovaries |
| Cell division | Meiosis | Meiosis |
| Cells formed | 4 sperm | 1 egg + 3 polar bodies |
| Size & mobility | Small, fast, motile | Large, immobile |
| When produced | Continuously from puberty | Monthly after puberty |
Genetic Variation through Crossing Over
What is Genetic Variation?
Genetic variation means differences in DNA among individuals.
It explains why we all look and function a little differently – even in the same family!
How Does Meiosis Create Variation?
During meiosis (the cell division that makes gametes), special steps mix up genes, making each egg or sperm slightly different.
One of the most important steps that creates variation is called crossing over.
What is Crossing Over?
Crossing over happens during Prophase I of meiosis, when homologous chromosomes pair up and swap sections of their DNA.
Step-by-step:
- Chromosomes come together in homologous pairs (same size and gene position)
- They touch and cross at a point called the chiasma
- Equal segments of DNA are exchanged between them
- Result: New combinations of genes on each chromosome
Why Is Crossing Over Important?
| Benefit | Explanation |
|---|---|
| Creates variation | Mixes genes in new ways so no two gametes are the same |
| Increases genetic diversity | Leads to differences in offspring, even from the same parents |
| Supports evolution | More variation = more chances for survival and adaptation |
Why Genetic Variation Matters
- It helps populations adapt to new environments
- It protects species from being wiped out by disease or climate change
- It ensures that each individual is genetically unique – important for natural selection
Key Points
- Crossing over = exchange of DNA between homologous chromosomes
- Happens during Prophase I of meiosis
- Produces new gene combinations
- Increases genetic variation in gametes
- Essential for evolution, survival, and healthy reproduction
Mitosis vs Meiosis
Why Compare Them?
Both mitosis and meiosis are types of cell division, but they serve very different purposes in the body.
Meiosis = Making gametes for reproduction, with variation
Comparison Table – Mitosis vs Meiosis
| Feature | Mitosis | Meiosis |
|---|---|---|
| Purpose | Growth, repair, replacement | Sexual reproduction (gamete formation) |
| Where it occurs | All body (somatic) cells | Only in reproductive organs (testes/ovaries) |
| Number of divisions | 1 division | 2 divisions |
| Cells produced | 2 identical cells | 4 genetically different gametes |
| Chromosome number | Same as parent (diploid: 2n) | Half of parent (haploid: n) |
| Genetic variation? | No – clones | Yes – through crossing over and assortment |
| Used for | Healing wounds, growing taller | Making sperm and egg cells |
| Type of cells made | Body cells | Sex cells (gametes) |
| Daughter cells identical? | Yes | No |
Key Differences
| Task Type | Mitosis | Meiosis |
|---|---|---|
| Purpose | Mitosis keeps the body growing and repairing itself. | Meiosis prepares for the next generation. |
| Number of Divisions | 1 split → 2 cells | 2 splits → 4 cells |
| Genetic Variation | Mitosis makes exact copies (like photocopying) | Meiosis mixes genes → genetic variety |
| Chromosome Number | Mitosis: 46 → 46 | Meiosis: 46 → 23 (in humans) |
Summary – Mitosis vs Meiosis
| Mitosis | Meiosis |
|---|---|
| Makes body cells | Makes sex cells (gametes) |
| 2 identical cells | 4 non-identical gametes |
| No variation | Variation due to crossing over |
| One round of division | Two rounds of division |
| Same chromosome number | Half chromosome number |
Summary:
- Mitosis is for everyday cell needs like growing and healing.
- Meiosis is for creating gametes, ensuring each one is unique.
- Both are vital for life – just in different ways.