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Meiotic Cell Division

Meiotic Cell Division. Sexual Reproduction. 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.

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Meiotic Cell Division

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  1. Meiotic Cell Division

  2. Sexual Reproduction • 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

  3. Gametes • 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)

  4. 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 How Does One Make a Haploid Gamete?

  5. 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 MitosisvsMeiosis

  6. Meiosis • Meiosis begins after a cell has progressed through G1, S, & G2 • Meiosis involves two successive divisions • Meiosis I and II • Each of these is subdivided into • Prophase • Metaphase • Anaphase • Telophase 3-44

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

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

  9. Synaptonemal Complex

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

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

  12. Figure 3.13 • Bivalents are organized along the metaphase plate • Homologous pairs 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

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

  14. 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 Meiosis

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

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

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

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