1. Meiotic Cell Division

2. Sexual reproduction is the most common way for eukaryotic organisms to produce offspring Parents make gametes with half the amount of genetic material (haploid) These gametes fuse with each other during fertilization to generate a new organism Sexual Reproduction

3. Simple eukaryotes are isogamous –They produce gametes that are morphologically similar Most eukaryotic species are heterogamous –These produce gametes that are morphologically different Sperm cells –Relatively small and mobile Oocytes or ova –Usually large and nonmobile –Store large amounts of nutrients Microspores (Pollen) Macrospores (Ovules) Gametes

4. How Does One Make a Haploid Gamete? Answer – meiosis Haploid cells are produced from diploid cells during gametogenesis The chromosomes must be distributed to reduce the chromosome number to half its original value but simultaneously sorted to assure that each chromosome (& its genes) is represented in each gamete

5. Mitosis vs Meiosis Produces two diploid daughter cells Produces daughter cells that ARE genetically identical Produce four haploid daughter cells Produces daughter cells that are NOT genetically identical

6. Meiosis begins after a cell has progressed through G 1, S, & G 2 Meiosis involves two successive divisions –Meiosis I and II –Each of these is subdivided into Prophase Metaphase Anaphase Telophase 3-44 Meiosis

7. Prophase I is further subdivided into periods known as –Leptotena –Zygotena –Pachytena –Diplotena –Diakinesis

8. A recognition process A total of 4 chromatids Figure 3.11 Periods of Prophase I

9. Synaptonemal Complex

10. A physical exchange of chromosome pieces A tetrad 2 bivalents Periods of Prophase I

11. Spindle apparatus complete; pairs of chromatids attached to kinetochore microtubules Stages of Meiosis I

12. Bivalents are organized along the metaphase plate Homologous p airs of sister chromatids aligned side by side –A pair of sister chromatids is linked to one of the poles –And the homologous pair is linked to the opposite pole –The arrangement is random with regards to the (blue and red) homologues Figure 3.13

13. 3-50 Pairs of sister chromatids separate from each other The centromere remains between sister chromatids Stages of Meiosis I

14. Meiosis Telophase I & cytokinesis of meiosis I is followed meiosis II Meiosis I has reduced the number of chromosomes in the daughter cells to the ½ the diploid number However, each homolog is still composed of 2 recombinant sister chromatids –The genetic content is still 2n Meiosis II reduces the genetic content to n

15. Stages of Meiosis II 1 of each type of chromosome (n) in each daughter cell (gamete)

16. Separation of Alleles During Meiosis Prophase I Metaphase I Anaphase I Telophase I Meiosis II Haploid cells Heterozygous (Yy) cell from a plant with yellow seeds y y y yy y y Y Y Y Y YY Y

17. Meiosis I Meiosis II or 2 Ry :: Heterozygous diploid cell (YyRr) to undergo meiosis y y y y y y y y y Y YY Y Y Y Y Y Y R R R r r y r r R R Y R R R R y R r rr r Y r Y y R r R r r 2 rY2 ry 2 RY Separation of Alleles During Meiosis