13.1 Types of Reproduction

A free GCSE Biology lesson for AQA (8461) from OBA School: asexual and sexual reproduction, gametes, clones and variation. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe asexual reproduction: one parent, mitosis only and genetically identical offspring (clones)
• Describe sexual reproduction: two parents, gametes made by meiosis, fertilisation and variation
• Name the gametes in animals and in flowering plants
• Compare the two types of reproduction and classify examples
• Work out how fast a population grows when cells divide by repeated doubling

Key words

• Asexual reproduction: Reproduction with one parent and no joining of gametes. The offspring get exactly the same genetic information as the parent.
• Sexual reproduction: Reproduction where a male gamete and a female gamete join. Genetic information from two parents is mixed.
• Gamete: A sex cell. Sperm and egg cells in animals; pollen and egg cells in flowering plants.
• Fertilisation: The joining (fusion) of a male gamete and a female gamete to form a fertilised egg (zygote).
• Clone: An organism that is genetically identical to its parent or to other offspring.
• Mitosis: Cell division that makes two genetically identical cells. Used for growth, repair and asexual reproduction.
• Meiosis: Cell division that makes four genetically different gametes, each with half the number of chromosomes.
• Variation: Differences between individuals of the same species.

Asexual reproduction

In asexual reproduction there is only one parent and no fusion of gametes. There is no mixing of genetic information, so the offspring are genetically identical to the parent. They are clones.

Only mitosis is involved. The parent copies its chromosomes and divides, so every new cell gets a full, identical set.

• Strawberry plant; How it reproduces asexually grows runners (side stems) along the ground; new plantlets form where they touch the soil
• Potato; How it reproduces asexually new plants grow from tubers (swollen underground stems)
• Daffodil; How it reproduces asexually its bulb divides to make new bulbs
• Yeast (a single-celled fungus); How it reproduces asexually grows a small bud that breaks off as a new cell
• Bacteria; How it reproduces asexually split in two by binary fission

Exam tip: Clones have identical genes, but they can still look different if they grow in different conditions (for example, more light or water). That difference is caused by the environment, not by genes.

Sexual reproduction

In sexual reproduction a male gamete and a female gamete join at fertilisation. Gametes are made by meiosis, so each gamete carries half of the parent's genetic information.

The fertilised egg gets a mixture of genetic information from two parents. This produces variation in the offspring: brothers and sisters are similar but not identical.

• Animals; Male gamete sperm cell; Female gamete egg cell (ovum)
• Flowering plants; Male gamete pollen (carries the male nucleus); Female gamete egg cell (inside the ovule)

Key fact: A plant that pollinates itself is still reproducing sexually: gametes are made by meiosis and they fuse.

Comparing the two types

• Number of parents; Asexual one; Sexual usually two
• Gametes?; Asexual no; Sexual yes: they fuse at fertilisation
• Cell division; Asexual mitosis only; Sexual meiosis to make gametes, then mitosis as the offspring grows
• Offspring; Asexual clones of the parent; Sexual genetically different from parents and each other
• Variation; Asexual none (only from the environment); Sexual lots

Worked example: classify it

A spider plant grows long stems with small plants at the tips. The small plants root and grow. Which type of reproduction is this? Give a reason.
Only one parent is involved and no gametes join, so the new plants are clones.

Answer: asexual reproduction

How fast asexual populations grow

Asexual reproduction can be very fast. If every cell divides in two each time, the number of cells doubles. After n divisions one cell has become 2ⁿ cells.

Worked example: bacteria doubling

One bacterium divides every 20 minutes. How many bacteria are there after 3 hours?
Number of divisions = 180 ÷ 20 = 9.
Number of bacteria = 2⁹ = 512.

Answer: 512 bacteria

Exam tip: Count the divisions first (total time ÷ time per division), then use 2ⁿ. Do not multiply by 2 the number of hours.

Common mistakes

• Saying asexual reproduction uses meiosis. Only mitosis is involved.
• Calling pollen the female gamete. Pollen carries the male gamete; the egg cell is female.
• Thinking clones must look identical. The environment can still cause differences.
• Saying self-pollination is asexual. Gametes still fuse, so it is sexual reproduction.
• Mixing up the words: fertilisation is the fusion of gametes, not the making of gametes.

Revision questions

Try these, then check your answers below each one.

Question 1. Which statement describes asexual reproduction? (Choose from: One parent, no fusion of gametes, offspring are clones, Two parents, gametes fuse, offspring show variation, One parent, gametes made by meiosis fuse together, Two parents, offspring are genetically identical clones.)

Answer: One parent, no fusion of gametes, offspring are clones

Working: Asexual reproduction needs one parent and no gametes. Only mitosis is involved, so the offspring are genetically identical clones.

Question 2. True or false? A pea flower that pollinates itself is reproducing asexually.

Answer: False

Working: Gametes are made by meiosis and they fuse at fertilisation, so self-pollination is still sexual reproduction.

Question 3. Name the type of cell division used in asexual reproduction.

Answer: mitosis

Working: Asexual reproduction uses mitosis only, so all the offspring are clones.

Related lessons

• Previous lesson: 12.5 Kidney Transplants
• Next lesson: 13.2 Cell Division in Sexual Reproduction
• In this chapter: 13.3 The Best of Both Worlds
• In this chapter: 13.4 DNA and the Genome
• In this chapter: 13.5 DNA Structure and Protein Synthesis

Continue in the full course

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