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Meiosis

Meiosis. Meiosis. Defined : Process where the chromosome number is reduced by half Gametes created (egg & sperm) End Result : Four Haploid Cells. Interphase. Same process G1: Growth S: Chromatin duplicated G2: Growth. Synthesis (S stage). Chromatin strands duplicated. Prophase 1.

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Meiosis

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  1. Meiosis

  2. Meiosis • Defined: Process where the chromosome number is reduced by half • Gametes created (egg & sperm) • End Result: Four Haploid Cells

  3. Interphase • Same process • G1: Growth • S: Chromatin duplicated • G2: Growth

  4. Synthesis (S stage) Chromatin strands duplicated

  5. Prophase 1 Mom 1 • Similar as mitosis, except… • Two Events: • 1) Synapsis: Pairing of homologous chromosomes • Dad’s #1 chromosome pairs with Mom’s #1, etc… • The four paired chromatids equals a TETRAD • 2) Crossing Over: Exchange of genes Dad 1

  6. Early Prophase Dad #3 Chromosomes form Dad #2 Dad #1 Mom #3 Mom #1 Mom #2 Nucleus dissolves

  7. Synapsis tetrad tetrad Dad #3 Spindle fibers pull homologous chromosomes together Dad #2 Dad #1 Mom #3 Mom #1 Mom #2 tetrad

  8. Metaphase 1 • Homologous chromosomes (tetrads) align along cell equator Dad #3 Mom #3 Mom #2 Dad #2 Mom #1 Dad #1

  9. Anaphase 1 • Tetrads separated • Homologous chromosomes are pulled to opposite ends Mom #2 Dad #2 Mom #1 Dad #1 Dad #3 Mom #3

  10. Telophase 1 • Cytokinesis divides the cells • Each cell contains 1 of the homologous chromosomes • Humans: 23 full chromosomes each Mom #2 Dad #2 Mom #1 Dad #1 Dad #3 Mom #3

  11. Prophase 2 • Same as mitosis • Note: No new DNA was created (no 2nd interphase) Mom #2 Dad #2 Mom#1 Dad #1 Dad #3 Mom #3

  12. Metaphase 2 • Remaining chromosomes are aligned at cell equator Mom #2 Dad #2 Mom #1 Dad #1 Dad #3 Mom #3

  13. Anaphase 2 • Sister chromatids are pulled to opposite ends

  14. Telophase 2 • Cytokinesis divides the cells • Nucleus reforms on the four new cells • Chromatids uncoil • End Result: Four haploid cells

  15. Mitosis vs. Meiosis

  16. spermatogonium Spermatogenesis Meiosis 1 • Defined: Production of sperm cells • Location: male testes • Makes final changes to sperm cell • Four haploid sperm cells at a time Meiosis 2 Spermatogenesis

  17. Spermatogenesis Video Clip

  18. oocyte Oogenesis Meiosis 1 • Defined: Production of the egg cell (ovum) • In female ovaries • During meiosis I: Cytoplasm distributed unequally • After meiosis II: • 1 cell matures • 3 “Polar Bodies” dissolve Meiosis 2 Oogenesis

  19. Oogenesis Video Clip

  20. Division of somatic cells Ex: Blood cells, skin cells, nerve cells… End Result: 2 Diploid Cells Importance: Replaces aging cells Importance: Form of asexual reproduction Division of gametes Ex: Sperm and Egg cells End Result: 4 Haploid cells Importance: Reduces the gamete chromosome number by half Mitosis Meiosis

  21. Kobe Kuiz 1) Name three ways that meiosis and mitosis differ. 2) Pick a stage of meiosis…any stage. Describe what happens in it. 3) What type of cells does meiosis create? 4) What are homologous chromosomes? 5) When do homologous chromosomes move to opposite ends of the cell? 6) When do chromatids move to opposite ends of the cell? 7) Why is no DNA created in meiosis 2? 8) How does meiosis differ in males vs. females?

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