What is the difference between sexual and asexual reproduction in the context of IB MYP Science?

In IB MYP Science, sexual reproduction involves two parents and the fusion of gametes, resulting in offspring with genetic variation. Asexual reproduction involves a single parent and produces genetically identical offspring, as there is no fusion of gametes. This distinction is crucial for understanding how genetic diversity is achieved in populations.

How does reproduction contribute to genetic inheritance?

Reproduction is fundamental to genetic inheritance as it allows the transfer of genetic information from parents to offspring. In sexual reproduction, offspring inherit a combination of genes from both parents, leading to genetic variation. This variation is essential for evolution and adaptation. In asexual reproduction, the genetic material is copied directly, resulting in identical offspring unless mutations occur.

Why is genetic variation important in sexual reproduction?

Genetic variation is important in sexual reproduction because it increases a population's ability to adapt to changing environments. It results from the combination of different alleles during gamete formation and fertilization. This variation can lead to beneficial traits that enhance survival and reproduction, which is a key concept in the study of inheritance and evolution in the IB MYP curriculum.

What role do chromosomes play in reproduction and inheritance?

Chromosomes are structures within cells that contain DNA, the molecule that carries genetic information. During reproduction, chromosomes ensure that DNA is accurately copied and distributed to offspring. In sexual reproduction, each parent contributes one set of chromosomes, which combine to form a complete set in the offspring. This process is crucial for maintaining genetic continuity and diversity across generations.

How do environmental factors influence reproduction and inheritance?

Environmental factors can significantly influence reproduction and inheritance by affecting the availability of resources, mating patterns, and the survival of offspring. For instance, temperature, food supply, and habitat conditions can impact reproductive success and the expression of inherited traits. Understanding these influences helps students in the IB MYP program appreciate the complex interactions between organisms and their environments.

Why is "Saying asexual reproduction doesn't involve cell division." a common mistake in Reproduction?

Why it happens: No partner involved. How to avoid it: Asexual reproduction IS cell division — by MITOSIS. The result is just identical clones rather than genetically-unique offspring.

Why is "Calling gametes diploid." a common mistake in Reproduction?

Why it happens: Most body cells are diploid. How to avoid it: Gametes are HAPLOID (half chromosome set, 23 in humans). Only when sperm + egg fuse does the diploid zygote form.

InheritanceIB MYP Sciences (Years 1-5)

Reproduction

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Reproduction — IB MYP Sciences: sexual vs asexual, gametes and fertilisation

Reproduction passes life on to the next generation. This MYP Sciences note covers the two main strategies (sexual and asexual), how gametes form by meiosis, and what happens at fertilisation.

What you’ll learn

Mapped to the IB MYP Sciences subject guide (2026 onwards).

MYP Sciences A — Distinguish asexual and sexual reproduction.
MYP Sciences A — Describe gametes and fertilisation.
MYP Sciences A — State the role of meiosis in reproduction.
MYP Sciences D — Evaluate when asexual or sexual reproduction is advantageous.

Two strategies

Asexual: one parent, clones. Sexual: two parents, variety.

Asexual reproduction:

ONE parent.
Offspring are GENETICALLY IDENTICAL clones.
Uses MITOSIS only.
Fast, no need to find a partner.
Examples: bacterial cell division, hydra budding, strawberry runners, potato tubers.

Sexual reproduction:

TWO parents contribute genetic material (gametes).
Offspring are GENETICALLY UNIQUE — combine some features from each parent.
Uses MEIOSIS to make gametes and FERTILISATION to combine them.
Slower, requires finding a mate.
Universal in mammals; common in plants (via pollen + ovule).

Feature	Asexual	Sexual
Parents	1	2
Offspring	identical clones	unique combinations
Speed	fast	slow
Energy cost	low	high
Variation	low	high → drives evolution

When is each best?

Asexual: when conditions are good and stable — fast colonisation. Many plants use this (e.g. strawberries spreading via runners).
Sexual: when environments change — variation gives some offspring a survival edge in new conditions.
Many organisms (plants, jellyfish, some lizards) can switch between depending on conditions.

Asexual: 1 parent, clones, fast. By mitosis.
Sexual: 2 parents, unique offspring. Requires meiosis + fertilisation.
Asexual good for stable conditions; sexual good for changing conditions.

Gametes, meiosis and fertilisation

Half chromosome set → fuse to make full set.

Gametes (sex cells) are produced by MEIOSIS — a special cell division that:

Produces FOUR daughter cells from one.
HALVES the chromosome number (each gamete is HAPLOID — 23 chromosomes in humans).
Shuffles the genes → every gamete is GENETICALLY UNIQUE.

Male gametes are sperm (small, lots produced, motile). Female gametes are eggs/ova (much larger, fewer made, contain nutrients for the embryo).

Fertilisation: a sperm fuses with an egg. The resulting zygote has the full DIPLOID set of 46 chromosomes (23 from each parent).

The zygote then divides by MITOSIS to grow into an embryo, then fetus, then a baby — each cell still carrying that mix of mother and father chromosomes.

Plants reproduce sexually too: pollen (male gamete) lands on a stigma, pollen tube grows down to fertilise the ovule (female gamete) → seed → new plant.

MYP criterion D classic: 'Why is sexual reproduction so common despite being slower than asexual?' Answer: because the VARIATION it produces is the raw material for evolution. In a changing world, the species that can adapt are the ones that survive. Variation is so valuable that the cost of sex (finding a mate, halving genetic contribution) is worth it for most organisms.

Meiosis: 1 cell → 4 haploid gametes, each genetically unique.
Fertilisation: sperm + egg → diploid zygote.
Zygote grows by mitosis into the new individual.

How it’s examined

Criterion A asks for definitions and contrasts. Criterion D often asks about when asexual or sexual is more advantageous.

Sources: IB MYP Sciences guide (IBO, official subject guide). Last reviewed 2026-05-25.

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Step-by-step worked examples — Reproduction

Step-by-step solutions to past-paper-style questions on reproduction, written exactly the way a tutor would explain them at the board.

1Asexual or sexual?
Getting started• classification
Question
Classify each as sexual or asexual: (a) human birth, (b) strawberry runners, (c) bacterial division, (d) flowering of an apple tree.
Step-by-step solution
1. Step 1
  (a) Sperm + egg → sexual.
2. Step 2
  (b) Runner forms new plant from one parent → asexual.
3. Step 3
  (c) One cell splits in two → asexual.
4. Step 4
  (d) Pollen + ovule → sexual.
Answer
(a) sexual, (b) asexual, (c) asexual, (d) sexual.
2Which division makes gametes?
Building confidence• meiosis
Question
Why is meiosis (not mitosis) used to make sex cells?
Step-by-step solution
1. Step 1
  Mitosis makes IDENTICAL diploid (46-chromosome) cells. If both parents passed 46, the child would have 92.
2. Step 2
  Meiosis HALVES the chromosome number → 23 chromosomes per gamete. Fertilisation restores 46.
3. Step 3
  Meiosis also shuffles genes, giving genetic VARIATION.
Answer
Meiosis halves the chromosome number AND introduces variation. Mitosis would keep doubling the chromosome count generation after generation.
3When is asexual better?
Stretch• evolution
Question
In what conditions is asexual reproduction MORE advantageous than sexual?
Step-by-step solution
1. Step 1
  When the environment is STABLE — variation isn't needed.
2. Step 2
  When colonising rapidly — making many quick copies beats finding mates.
3. Step 3
  When the parent is well-adapted to current conditions — copies will be too.
Answer
Stable environment, rapid colonisation, well-adapted parent. Sexual reproduction is better when the environment changes.

Key Definitions and Keywords — Reproduction

Definitions to memorise and the exact keywords mark schemes credit for reproduction answers — sharpened from recent examiner reports for the 2026 IB MYP Sciences sitting.

Asexual reproduction
Examiner keyword
Reproduction involving one parent; offspring are genetically identical clones.
Sexual reproduction
Examiner keyword
Reproduction involving two parents and the fusion of gametes; offspring are genetically unique.
Gamete
Examiner keyword
A sex cell (sperm or egg) that is haploid — half the normal chromosome number.
Fertilisation
Examiner keyword
Fusion of a male and female gamete to produce a diploid zygote.
Zygote
Examiner keyword
The single cell formed by fertilisation; develops into the new individual.

Common Mistakes and Misconceptions — Reproduction

The traps other students keep falling into on reproduction questions — taken from recent IB MYP Sciences examiner reports and mark schemes — and how to avoid them.

✕Saying asexual reproduction doesn't involve cell division.
Why it happens
No partner involved.
How to avoid it
Asexual reproduction IS cell division — by MITOSIS. The result is just identical clones rather than genetically-unique offspring.
✕Calling gametes diploid.
Why it happens
Most body cells are diploid.
How to avoid it
Gametes are HAPLOID (half chromosome set, 23 in humans). Only when sperm + egg fuse does the diploid zygote form.

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Reproduction — frequently asked questions

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Reproduction

Short Study Notes in the form of Slides

Short Study Notes — Reproduction

Detailed Notes

What you’ll learn

How it’s examined

1Asexual or sexual?

2Which division makes gametes?

3When is asexual better?

Asexual reproduction

Sexual reproduction

Gamete

Fertilisation

Zygote

✕Saying asexual reproduction doesn't involve cell division.

✕Calling gametes diploid.

Practice questions

Past paper style quiz

Assess your understanding

Reproduction — frequently asked questions