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Meiosis

Meiosis. Mitosis vs. Meiosis. Meiosis. 1 replication of chromosomes, in interphase , followed by 2 cell divisions Occurs in plants and animals that reproduce sexually Usually occurs in specialized sex organs – ovaries and testes. Mieosis. Gametes –

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Meiosis

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  1. Meiosis

  2. Mitosis vs. Meiosis

  3. Meiosis • 1 replication of chromosomes, in interphase, followed by 2 cell divisions • Occurs in plants and animals that reproduce sexually • Usually occurs in specialized sex organs – ovaries and testes

  4. Mieosis • Gametes – • Specialized cells that participate in sexual reproduction • Sperm and egg

  5. Homologous Chromosomes • Pair of chromosomes that are the same length and shape • Carry the same types of genes • Humans get one from each parent

  6. Counting Chromosomes • Humans have 23 types of chromosomes • One of each type from each parent gamete • 23 (mom) + 23 (dad) = 46 total chromosomes • This is the Diploid (2n) number • Diploid – 2 chromosomes, one homologous pair • In humans 2n = 46

  7. Counting Chromosomes • Gametes have only one set of chromosomes • Haploid (n) – 1 chromosome from a homologous pair • In humans n = 23

  8. Stages of Meiosis • Both parts follow similar pattern • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis • Very similar to mitosis • Two parts – • Meiosis I • Meiosis II

  9. Stages of Meiosis

  10. Interphase I • Same as in mitosis • Chromatin replicate • Cell growth

  11. Prophase I • Chromosomes form • Homologous pairs come together • Crossing over occurs • Nuclear membrane starts to dissapate

  12. Metaphase I • Homologs move to the equator or metaphase plate

  13. Anaphase I • Homologs are separated and one from each pair moves toward opposite ends of the cell

  14. Telophase I and Cytokinesis • Chromosomes uncoil • Nuclear membrane reforms • Spindle fibers break down • Two daughter cells form • These cells are haploid • Only have one of each type of chromosome

  15. Meiosis II • Prophase II • Metaphase II • Anaphase II • Telophase II • Happens simultaneously in both daughter cells • No interphase – • Chromosomes are already duplicated • Same as Mitosis

  16. Meiosis II

  17. Meiosis Differences • Female – • Form one gamete during meiosis • Other three cells are broken down • Male – • form four gametes during meiosis

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