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Biology · Reproduction and Meiosis

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Biology · AQA Paper 2

Reproduction and Meiosis

Sexual and Asexual Reproduction

Some organisms need a partner to reproduce, and others can reproduce alone.

  • Sexual reproduction Reproduction that involves the fusion of male and female gametes.
  • Asexual reproduction Reproduction that involves one parent, and no fusion of gametes.
  • Gamete A sex cell, such as a sperm cell or an egg cell.
Asexual reproduction with one parent producing identical clones, and sexual reproduction with two parents producing different offspring.
Asexual reproduction gives identical clones, and sexual reproduction gives variety.

Sexual and asexual reproduction

  • Sexual reproduction Two parents; Gametes, made by meiosis, fuse; Genetic information is mixed
  • Asexual reproduction One parent; No gametes, and only mitosis; No mixing of genetic information

Meiosis and Fertilisation

A human sperm cell and a human egg cell each have only half of the chromosomes of an ordinary body cell.

  • Meiosis Cell division in the reproductive organs that forms four genetically different gametes.
  • Gamete A sex cell with half the number of chromosomes of a body cell.
  • Fertilisation The fusion of the nuclei of a gamete from each parent.
A body cell with two pairs of chromosomes dividing by meiosis to form four different gametes, each with one chromosome from each pair.
Meiosis makes four genetically different gametes, with half the number of chromosomes.

Gametes and body cells

  • Gamete (sperm or egg) Made by meiosis; Half the number of chromosomes; 23 chromosomes in humans
  • Body cell Made by mitosis; Full number of chromosomes; 46 chromosomes in humans

Advantages and Disadvantages of Sexual and Asexual Reproduction (Separate only)

Some organisms reproduce only one way, but many use both, depending on the circumstances.

  • Variation Differences between the individuals of a population.
  • Natural selection The process by which the best adapted organisms survive and reproduce.
  • Selective breeding The process by which humans breed plants and animals for particular characteristics.
Four examples of organisms that reproduce both asexually and sexually: malarial parasites, fungi, strawberry plants and daffodils.
Many organisms use both asexual and sexual reproduction, depending on the circumstances.

Sexual and asexual reproduction

  • Sexual reproduction Produces variation in the offspring; Gives a survival advantage if the environment changes; Can be speeded up by selective breeding
  • Asexual reproduction Only one parent is needed; More time and energy efficient; Faster