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Meiosis

Explore the process of meiosis in eukaryotic cells, where DNA is replicated, swapped, and organized, leading to the formation of genetically diverse gametes for sexual reproduction. Discover the key stages and highlights of meiosis, including genetic variation mechanisms like crossing over and independent assortment. Learn about the significance of haploid cells in creating gametes and the potential genetic disorders like Down syndrome resulting from meiotic errors.

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Meiosis

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  1. Meiosis AP Ch 13.1, 13.3, 46.4

  2. The moment of YOU! • Your first existence as a diploid organism • gamete + gamete = fertilized zygotic cell • 23 chromosomes from mom (inside egg cell) • 23 chromosomes from dad (inside sperm cell)

  3. Process: Gametic cell division (Meiosis) • Eukaryotic Cells • DNA is replicated, packaged, swapped, & organized! • Proteins control when the cell membrane divides twice! • Daughter cells are not identical to parent cells

  4. Major highlights in Meiosis • Interphase • G1 (growth) • S (replication of genetic material in S-phase) • G2 (prepare for division) • Meiosis I • Prophase I (synapsis and crossing over occurs) • Metaphase I (independent assortment of tetrads) • Anaphase I (homologous chromosomes separate) • Telophase I/Cytokinesis (round 1 division) • Meiosis II • Prophase II (no replication of DNA!) • Metaphase II (independent assortment of chromosomes) • Anaphase II (replicated chromatids separate) • Telophase II/Cytokinesis (round 2 division)

  5. Prophase 2

  6. Interphase • G1: normal growth and function • S: Replication! • G2: prepare for division

  7. Meiosis I: Prophase I • Synapsis: • Homologous Chromosomes form a tetrad • Crossing Over: • Sister chromatids exchange material at chiasmata • Contributing to genetic variation

  8. Meiosis I: Metaphase I • Microtubules from the centrosomes randomly organize tetrads along the equator (independent assortment) • Contributing to genetic variation

  9. Meiosis I: Anaphase I • Tetrads split apart • Sister chromatids are still attached at centromere

  10. Meiosis I: Telophase I & Cytokinesis • Two cells containing different genetic material separate • Interphase does not reoccur • Why?

  11. The result? • Four genetically different cells. • Each cell has 1 set of chromosomes • N chromosomes • Haploid cell • Gamete cell • Sex cells (sperm/egg)

  12. Example: Turkey Chromosomes A Turkey has 80 chromosomes in a body cell. How many chromosomes are in a mitotic cell? Diploid # = 80 Somatic # = 80 2N = 80

  13. Example: Turkey Chromosomes This turkey is about to make a baby! How many chromosomes are in its sperm cell? Haploid # = 40 Gamete # = 40 N = 40

  14. Problems with Meiosis • Nondisjunction: • Failure of homologues to separate • Aneuploidy: • an incorrect number of chromosomes in zygote • Ex: Down syndrome (trisomy 21)

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