1. MEIOSIS What is it? What is it? Making of gametes Making of gametes Sex Cells Sex Cells Sperm (pollen) in males Sperm (pollen) in males Eggs (ova) in females Eggs (ova) in females Diploid Haploid Diploid Haploid Involves: Involves: Cell division Cell division 2 nuclear divisions 2 nuclear divisions Reduction of chromosome number by half Reduction of chromosome number by half

2. The human life cycle Egg cell Sperm cell FERTILIZATIONMEIOSIS Mitosis and development Diploid zygote (2n = 46) Multicellular diploid adults (2n = 46) Haploid gametes (n = 23)

3. Chromosomes Centromere Sister chromatids Somatic cells of each species contain a specific number of chromosomes Human cells have 46, making up 23 pairs of homologous chromosomes In each homologous pair - ~ 1 comes from “Mom” ~ 1 comes from “Dad” Homologous Chromosomes

4. Interphase Just like “Interphase” of Mitosis Just like “Interphase” of Mitosis G 1 ~ ‘Gap’ 1 = growth and preparation G 1 ~ ‘Gap’ 1 = growth and preparation S ~ ‘Synthesis’ = DNA replication to make S ~ ‘Synthesis’ = DNA replication to make exact copies of the chromosomes G 2 ~ ‘Gap’ 2 = growth and shape change G 2 ~ ‘Gap’ 2 = growth and shape change

5. Meiosis I ~ Reduction Division Prophase I Prophase I Chromatin thickens into chromosomes Chromatin thickens into chromosomes You can now see them under a light microscope You can now see them under a light microscope Nuclear membrane begins to disintegrate Nuclear membrane begins to disintegrate Centrioles migrate to opposite poles Centrioles migrate to opposite poles Homologues do something unique to meiosis Homologues do something unique to meiosis

6. Prophase I - continued Homologous Pairs line up next to each other Homologous Pairs line up next to each other Synapsis Synapsis forms a tetrad forms a tetrad Crossing Over Crossing Over pieces of the chromosomes ‘switch’ places pieces of the chromosomes ‘switch’ places Stay connected at Chiasma(ta) Stay connected at Chiasma(ta) MOST IMPORTANT ~ for genetic diversity MOST IMPORTANT ~ for genetic diversity

8. Metaphase I Metaphase I Attached homologues line up on metaphase Attached homologues line up on metaphaseplate Anaphase I Anaphase I Tetrads separate at chiasma(ta) Tetrads separate at chiasma(ta) ** sister chromatids are STILL together ** sister chromatids are STILL together Telophase I Telophase I Homologues move to poles Homologues move to poles 2 nuclear membranes form (in some cells) 2 nuclear membranes form (in some cells) ** Chromosome number is now HAPLOID ~ there is now half the number of original chromosomes from the parent.

10. Interkinesis Stage between Meiosis I and II Stage between Meiosis I and II Resting stage Resting stage NOT another Interphase NOT another Interphase NO DNA replication NO DNA replication Strictly a “recovery” phase or Strictly a “recovery” phase or rest period before moving on.

11. Meiosis II – like Mitosis Prophase II Prophase II Just like Meiosis I – but NO crossing over Just like Meiosis I – but NO crossing over Metaphase II Metaphase II Sister chromatids line up on metaphase plate Sister chromatids line up on metaphase plate Usually at right angles to meiosis I Usually at right angles to meiosis I Anaphase II Anaphase II Sister chromatids separate at centromere and Sister chromatids separate at centromere and move to opposite poles move to opposite poles Telophase II and Cytokinesis Telophase II and Cytokinesis 4 new nuclei are formed 4 new nuclei are formed Each are haploid Each are haploid

13. Crossing Over = Genetic Diversity

14. Mitosis and Meiosis Compared

15. WEB LINKS http://www.lewport.wnyric.org/jwanamaker/ animations/meiosis.html http://www.lewport.wnyric.org/jwanamaker/ animations/meiosis.html http://www.lewport.wnyric.org/jwanamaker/ animations/meiosis.html http://www.lewport.wnyric.org/jwanamaker/ animations/meiosis.html http://www3.telus.net/byngscience/sc10/Sc1 0~Biology/s_tan_division.swf http://www3.telus.net/byngscience/sc10/Sc1 0~Biology/s_tan_division.swf http://www3.telus.net/byngscience/sc10/Sc1 0~Biology/s_tan_division.swf http://www3.telus.net/byngscience/sc10/Sc1 0~Biology/s_tan_division.swf http://www.pbs.org/wgbh/nova/baby/divi_fl ash.html http://www.pbs.org/wgbh/nova/baby/divi_fl ash.html http://www.pbs.org/wgbh/nova/baby/divi_fl ash.html http://www.pbs.org/wgbh/nova/baby/divi_fl ash.html