Edexcel IGCSE Biology

Revision Notes

3.1 Sexual & Asexual Reproduction: Differences

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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

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

Feature Asexual Reproduction Sexual Reproduction
Number of parent organisms One Two
Type of cell division required to produce offspring Mitosis Meiosis
Level of genetic similarity between offspring Genetically identical to each other (and to the parent) Genetically unique (and genetically different from both parents)
Sources of genetic variation in offspring Only one source: mutation

Three sources:

  • The contribution of 50% of their DNA from each of the two parents
  • The production of gametes by meiosis (resulting in new combinations of alleles on the chromosomes)
  • The random assortment of chromosomes into gametes during meiosis
Number of offspring produced Usually relatively large numbers Usually relatively limited numbers
Time taken to produce offspring Usually relatively fast Usually relatively slowly

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Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.