1-Sexual & asexual reproduction

• Meiosis leads to non-identical cells being formed
• Mitosis leads to identical cells being formed
• Sexual reproduction involves the fusion of male and female gametes, such as:

  • animals: sperm, egg cells
  • Flowering plants: pollen, egg cells
• There is mixing of genetic information in sexual reproduction which leads to variety in the offspring
• Meiosis is involved in the formation of gametes
• Asexual reproduction only involves one parent with no fusion of gametes, as there is no fusion of genetic information, this leads to genetically identical offspring (clones)
• Only mitosis is involved in asexual reproduction
• Examples of organisms that use asexual reproduction:

  • bacteria
  • production of spores by fungi
  • some plants use runners (strawberries)
  • formation of tubers (potatoes)
  • formation of bulbs (daffodils)
  • budding (yeast)
• Asexual reproduction only involves mitosis to create genetically identical copies of the parent cell (clones)

  
• Mitosis is part of the cell cycle, which involves:

  • cell growth and the increase of the number of structures in the cell (organelles)
  • genetic material is copied (duplicated)
  • mitosis occurs leading to chromosome separation and cell division
• Mitosis is used for:

  • growth
  • repair to damaged tissue
  • replacement of worn-out cells
• During sexual reproduction, the nuclei of the male and female gametes are fused in order to create a zygote, this process is known as fertilisation
• Gametes are haploids which contain half number of chromosomes in each
• Embryo is a diploid which is formed when male and female gametes combine to create the full complement of chromosomes
• Gametes in flowering plants are pollen and egg cells (ovule)

  
• Bacteria use binary fission to reproduce asexually
• Plants are partially male and female but they usually cross fertilise to give variety in the offspring
• Advantages of sexual reproduction:

  • produces genetic variation in the offspring
  • the species can adapt to new environments due to variation, which gives them a survival advantage (evolve by Natural Selection)
  • a disease is less likely to affect all the individuals in a population
• Disadvantages of sexual reproduction:

  • time and energy are needed to find a mate
  • it is not possible for an isolated individual to reproduce
• Advantages of asexual reproduction:

  • the population can increase rapidly when the conditions are favourable
  • only one parent is needed
  • more time and energy efficient as don’t need a mate
  • faster than sexual reproduction
• Disadvantages of asexual reproduction:

  • does not lead to genetic variation in a population
  • the species may only be suited to one habitat
  • disease may affect all the individuals in a population
• How does yeast reproduce?

  Budding

  Asexual reproduction