♿ Mitosis
Makes cells that are identical to each other and to the parent cell. You met mitosis earlier in Chromosomes, Mitosis and the Cell Cycle.
Reproduction » Sexual and Asexual Reproduction
What you'll learn this session
Study time: 30 minutes
AQA spec: 4.6.1.1
- The difference between meiosis and mitosis, and the cells each one makes
- How sexual reproduction works and why it gives variety
- How asexual reproduction works and why it gives clones
- How to compare the two types of reproduction in an exam
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Unlock This CourseTwo ways to make a new living thing
Every living thing comes from other living things. Reproduction is how organisms make new individuals of their own kind. There are two main types: sexual and asexual. The big difference between them is what happens to the genetic information that is passed on. In one type it gets mixed. In the other it is simply copied.
Two kinds of cell division are involved, and you need to be able to tell them apart:
⚛ Meiosis
Makes cells that are non-identical. Each new cell has a different mixture of genetic information. Meiosis is used to make gametes.
Key terms:
- Meiosis: a type of cell division that leads to non-identical cells being formed.
- Gamete: a male or female sex cell, made by meiosis.
- Fusion: the joining together of a male gamete and a female gamete.
- Clone: an organism that is genetically identical to its parent.
Sexual reproduction
Sexual reproduction involves two parents. Each parent makes special sex cells called gametes. A male gamete and a female gamete then join together. This joining is called fusion. The fused cell contains genetic information from both parents and grows into the new offspring.
The gametes are different in animals and in flowering plants:
🐾 In animals
The male gamete is the sperm cell. The female gamete is the egg cell. A sperm cell and an egg cell fuse.
🌺 In flowering plants
The male gamete is found in pollen. The female gamete is the egg cell. A pollen cell and an egg cell fuse.
Gametes are made by meiosis. Because meiosis makes non-identical cells, no two gametes from the same parent carry exactly the same genetic information.
Why sexual reproduction gives variety
In sexual reproduction there is a mixing of genetic information. The offspring gets some of its genetic information from the father and some from the mother. This mix is different every time, so the offspring are not identical to each other or to either parent. This is called variety in the offspring.
Think about a family with brothers and sisters. They have the same two parents, but they are not copies of each other. That is sexual reproduction at work.
The chain of ideas
Meiosis makes non-identical gametes. Two gametes fuse. Genetic information from both parents is mixed. The offspring show variety.
Asexual reproduction
Asexual reproduction involves only one parent. There are no gametes and so there is no fusion. There is also no mixing of genetic information.
The new organism is made when cells of the parent divide by mitosis only. Mitosis makes identical cells, so the offspring have exactly the same genes as the parent. They are genetically identical offspring, called clones.
A strawberry plant is a good everyday example. It sends out side shoots called runners. New plants grow from the runners. Each new plant is a clone of the parent plant, so they all have the same genes.
Side by side
♀♂ Sexual
Two parents.
Gametes are made by meiosis.
Gametes fuse.
Genetic information is mixed.
Offspring show variety.
♾ Asexual
One parent.
No gametes and no fusion.
Only mitosis is involved.
No mixing of genetic information.
Offspring are clones.
Spot the type
Exam questions often describe a situation and ask you which type of reproduction it is. Look for clues in the wording:
- "Two parents", "sperm", "pollen" or "gametes fuse" means sexual reproduction.
- "One parent", "identical offspring" or "clones" means asexual reproduction.
- "Variety in the offspring" or "mixing of genetic information" means sexual reproduction.
- "Mitosis only" means asexual reproduction.
Remember that the fused cell in sexual reproduction still divides by mitosis to grow into a whole organism. The key point is that meiosis makes the gametes, and only sexual reproduction involves gametes.
Common mistakes
1. Saying that meiosis makes identical cells. It is mitosis that does that. Meiosis makes non-identical cells.
2. Writing that asexual reproduction uses gametes. It does not. There are no gametes and no fusion.
3. Saying that all reproduction needs two parents. Asexual reproduction needs only one.
4. Mixing up the plant gametes. In flowering plants the gametes are pollen and egg cells, not sperm and egg cells.
Worked example
Question: A gardener grows a new plant from a cutting taken from a parent plant. The new plant is a clone. Which type of cell division made the new cells, and why is the plant identical to its parent?
Answer: Mitosis made the new cells. Mitosis makes genetically identical cells, and there was no fusion of gametes and no mixing of genetic information, so the new plant has exactly the same genes as its parent.
Exam-style question
(a) Name the type of cell division that is used to make gametes. [1 mark]
(b) Name the two gametes that fuse in a flowering plant. [2 marks]
(c) Explain why the offspring from sexual reproduction are not genetically identical to their parents. [2 marks]
(d) Describe how asexual reproduction differs from sexual reproduction. [3 marks]
Model answer
(a) Meiosis (1).
(b) Pollen (cell) (1) and egg cell (1).
(c) Genetic information from two parents is mixed (1) so the offspring get a different combination of genes from either parent (1).
(d) Asexual reproduction involves only one parent, sexual involves two (1). There is no fusion of gametes in asexual reproduction (1). Asexual reproduction uses mitosis only and gives clones, so there is no mixing of genetic information and no variety (1).
Exam tip
In a "describe the difference" question, make each point a comparison: say what happens in sexual reproduction and what happens in asexual reproduction, not just one of them.