Edexcel IGCSE Biology: Double Science 复习笔记 3.1.1 Types of Reproduction

Edexcel IGCSE Biology: Double Science 复习笔记 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

  • 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



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






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 Table16.1-Advantages-_-Disadvantages-of-Asexual-Reproduction-table


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