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Chapter 18 Meiosis


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Chapter 18 Meiosis

  1. 1. Meiosis
  2. 2. Lesson Objectives(a) identify, with the aid of diagrams, the main stages of meiosis (Names of the sub-divisions of prophase are not required)(b) state how meiosis and fertilisation can lead to variation Use the knowledge gained in this section in new situations or to solve related problems.
  3. 3. Recap Mitosis MeiosisSame/different Same no. as Half the no. ofno. of parents chromosomeschromosomes(with regards to theirparent cells)Genetically Genetically Geneticidentical to identical variationparent cell?
  4. 4. How do we remember the stages of the cell cycle? I nterphase P rophase M etaphaseM A naphase T elophaseC ytokinesis
  5. 5. Overview of Mitosis
  6. 6. Overview of Meiosis• Is a form of nuclear division such that the daughter nuclei produced contain half the number of chromosomes as the parent nuclei• consists of 2 stages: Meiosis I and Meiosis II
  7. 7. Meiosis I (pg. 346 Bio Textbook))
  8. 8. Meiosis II
  9. 9. Questions:• Is there any similarity between meiosis and mitosis?• State the 2 processes that take place in meiosis that brings about genetic variation.
  10. 10. How is prophase I of meiosisdifferent from prophase of mitosis?1. Homologous chromosomes pair up (synapsis) forming a tetrad (a.k.a. bivalent)2. Formation of chiasmata. Crossing over takes place
  11. 11. Chiasmata (plural) (singular)
  12. 12. Crossing Over
  13. 13. Independent Assortment
  14. 14. Sperm production 23 chromosomes haploid (n) 23 chromosomes haploid (n)46 chromosomes 23 diploid chromosomes (2n) haploid (n) 23 chromosomes haploid (n) Definition of gamete: A reproductive cell containing the haploid number of chromosomes
  15. 15. Production of Eggs 23 chromosomes haploid (n)46 chromosomes diploid (2n)Variations in the gametes, together with random fertilizationproduce variations in the offspring
  16. 16. Sexual Reproduction fertilizationSperm + ovum zygote (n) (n) (2n) formed by meiosis in mitosis the gonads, testes and ovary embryo (2n)where n = haploid; 2n = diploid
  17. 17. That is why…
  18. 18. Test yourself• Attempt the MCQ worksheet given to you to assess your understanding of the lesson