reproduction

• meiosis leads to non-identical cells being formed while mitosis leads to identical cells being formed
• what is meiosis (sexual reproduction)?

  • involves the fusion of male and female gametes
  • sperm and egg cells in animals
  • pollen and eggs cells in plants
• in sexual reproduction there is a mixing of genetic information which leads to variety in the offspring. the formation of gametes involves meiosis.
• asexual reproduction involves only only one parent and no fusion of gametes. there is no mixing of genetic information. this leads to genetically identical offspring. only mitosis is involved.
• how does a cell divide to form gametes?

  • cells in reproductive organs divide by meiosis to form gametes
  • copies of the genetic information are made
  • the cell divides twice to form four gametes, each with a single set of chromosomes
  • all gametes are genetically different to each other
• gametes join at fertilisation to restore the normal number of chromosomes. the new cell divides by mitosis. the number of cells increases. as the embryo develops, cells differentiate
• advantages of sexual reproduction

  • produces variation in the offspring
  • if environment changes, variations gives a survival advantage by natural selection
  • natural selection can be sped up by humans in selective breeding to increase food production
• advantages of asexual reproduction?

  • one parent needed
  • more time and energy efficient as do not need to find a mate
  • many identical offspring can be produced when conditions are favourable
• which organisms reproduce by both methods?

  • malarial parasites reproduce asexually in the human host but sexually in the mosquito
  • many fungi reproduce asexually by spores but also reproduce sexually to give variation
  • many plants produce seeds sexually but also reproduce asexually by runners such as strawberry plants or bulb division such as daffodils.