Edexcel IGCSE Biology

Revision Notes

3.1.1 Types of Reproduction

Sexual Reproduction

  • Sexual reproduction is:

The process involving the fusion of the nuclei of two gametes to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other

  • Fertilisation is defined as the fusion of gamete nuclei, and as each gamete comes from a different parent, there is variation in the offspring

Gametes and zygotes

  • A gamete is a sex cell (in animals: sperm and ovum; in plants: pollen nucleus and ovum)
  • Gametes differ from normal cells as they contain half the number of chromosomes found in other body cells – we say they have a haploid nucleus
  • This is because they only contain one copy of each chromosome, rather than the two copies found in other body cells
  • In human beings, a normal body cell contains 46 chromosomes but each gamete contains 23 chromosomes
  • When the male and female gametes fuse, they become a zygote (fertilised egg cell)
  • This contains the full 46 chromosomes, half of which came from the father and half from the mother – we say the zygote has a diploid nucleus

Advantages and disadvantages of sexual reproduction

  • Although there are some clear advantages of sexual reproduction (in comparison to asexual reproduction), there are also a few disadvantages of sexual reproduction

Advantages & Disadvantages of Sexual Reproduction Table

Advantages & Disadvantages of Sexual Reproduction table, IGCSE & GCSE Biology revision notes

Asexual Reproduction

  • Asexual reproduction is:

The process resulting in genetically identical offspring being produced from one parent

  • Asexual reproduction does not involve gametes or fertilisation
  • Only one parent is required so there is no fusion of gametes and no mixing of genetic information
  • As a result, the offspring are genetically identical to the parent and to each other (they are clones)
  • Many plants reproduce via asexual reproduction
  • Bacteria produce exact genetic copies of themselves in a type of asexual reproduction called binary fission

Binary fission in bacteria, IGCSE & GCSE Biology revision notes

Bacteria produce exact genetic copies of themselves in a type of asexual reproduction called binary fission

Advantages and disadvantages of asexual reproduction

  • Whilst asexual reproduction has several advantages over sexual reproduction, it also has a few disadvantages

Advantages & Disadvantages of Asexual Reproduction TableAdvantages & Disadvantages of Asexual Reproduction table, IGCSE & GCSE Biology revision notes

Comparing Sexual & Asexual Reproduction

  • The key differences between sexual and asexual reproduction include:
    • The number of parent organisms
    • How offspring are produced (the type of cell division required)
    • The level of genetic similarity between offspring
    • The possible sources of genetic variation in offspring
    • The number of offspring produced
    • The time taken to produce offspring

Comparing Sexual & Asexual Reproduction Table

Sexual and asexual reproduction comparison_1, downloadable IGCSE & GCSE Biology revision notes

Author:

Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.
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