Sexual and asexual reproduction, meiosis

• What is sexual reproduction?

  • involves the production of gametes by meiosis
  • a gamete from each parent fuses to form a zygote
  • genetic information from each gamete is mixed so the resulting zygote is unique
• What are gametes?

  • sex cells (sperm and egg cells in animals, pollen and egg cells in flowering plants)
  • haploid (half the number of chromosomes)
• What is meiosis?

  • form of cell division involved in the formation of gametes in reproductive organs
  • chromosome number is halved
  • involves 2 divisions
• What must occur prior to meiosis?

  interphase - copies of genetic information are made during this process
• what happens during the first stage of meiosis?

  • chromosome pairs line up along the cell equator
  • pair of chromosomes are separated and move to opposite poles of the cell
  • chromosome number is halved
• what happens during the second stage of meiosis?

  • chromosomes line up along the cell equator
  • chromatids are separated and move to opposite poles of the cell
  • four unique haploid gametes are produced
• why is meiosis important for sexual reproduction?

  • increases genetic variation
  • ensures that the zygote formed at fertilisation is diploid
• describe fertilisation and its resulting outcome

  • gametes join together to restore the normal number of chromosomes and the new cell then divides by mitosis
  • as the embryo develops, cells differentiate
• advantage of sexual reproduction

  • creates genetic variation in offspring, increasing chances of species adapting and surviving environmental changes
  • natural selection can be speeded up by humans in selective breeding to increase food production
• disadvantages of sexual reproduction

  • two parents required making reproduction difficult in endangered populations or in species which have solitary lifestyles
  • more time and energy is required so fewer offspring are produced
• What is asexual reproduction?

  • involves mitosis only
  • produces genetically identical offspring known as daughter cells
• advantages of asexual reproduction

  • 1 parent required
  • lots of offspring produced quickly, enabling rapid colonisation of an area and reducing competition from other species
  • requires less energy and time as don’t need mate
• disadvantage of asexual reproduction

  no genetic variation reducing the chances of a species being able to adapt to environmental change
• describe the circumstances in which malarial parasites reproduce sexually and asexually

  sexual in mosquito

  asexual in human host
• describe the circumstances in which fungi and plants reproduce sexually and asexually

  • Asexually: spores, seeds
  • sexually: to give variation, runner or bulb division