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Meiosis

Meiosis. AP Ch 13.1, 13.3, 46.4. 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). Process: Gametic cell division (Meiosis). Eukaryotic Cells

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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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