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Meiosis: The Creation of Four New Cells with Half the Chromosomes

Meiosis is a process of sexual reproduction that results in the creation of four new cells, each with half the number of chromosomes of the parents. This process involves the formation of tetrads, crossing over, and the separation of homologous chromosomes. Meiosis is divided into two stages: Meiosis I and Meiosis II.

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Meiosis: The Creation of Four New Cells with Half the Chromosomes

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  1. Meiosis

  2. Meiosis • Sexual Reproduction • The creation of four new cells with ½ (half) the number of chromosomes of the parents. • Example: Humans have 46 chromosomes each new cell only has 23 chromosomes • Sperm (23) + Egg (23) = 46 chromosomes

  3. Important words to know related to meiosis: • Homologous chromosomes= • 2 sets of chromosomes (4 chromosomes total) that have similar DNA sequences and come from separate parents. • Ex: one set comes from the mother and the other set comes from the father.

  4. Important words to know related to meiosis: • Diploid= means “two sets.” Cell that contains both sets of homologous chromosomes. • Represented by 2N • Haploid= means “one set.” Cell that contains one set of chromosomes. • Represented by N

  5. Interphase 1 Meiosis 1 Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Meiosis 2 Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 The stages of Meiosis

  6. Interphase 1 • Chromosomes Double • Organelles duplicate (make copies) • Cell grows

  7. Prophase 1 • Homologous chromosomes move together to form Tetrads • Tetrad= pairs of chromosomes • Nuclear Envelope (Membrane) disappears • Centrioles move apart forming Spindle Fibers

  8. Crossing Over • Occurs during meiosis. • Homologous chromosomes form a tetrad. • Chromatids cross over one another. • The crossed sections of the chromatids are exchanged.

  9. Crossing Over

  10. Metaphase 1 • Homologous pairs (tetrads) line up at the center of the cell • Centrioles are at the poles attached to each sister chromatid by spindle fibers

  11. Anaphase 1 • Homologous chromosomes move to poles of the cell • Sister chromosomes remain attached at the centromere

  12. Telophase 1 & Cytokinesis • Homologous chromosomes move to poles • Nuclear envelope reforms (sometimes) • Spindle apparatus disappears • Cells divide into TWO new cells (Cytokinesis)

  13. Meiosis 1 • Meiosis I Telophase I and Cytokinesis Prophase I Interphase I Metaphase I Anaphase I

  14. Prophase 2 • Nuclear envelope disappears (if there) • Spindle fibers reform

  15. Metaphase 2 • Sister Chromatids line up at the center of the cell • Centrioles at the ends of the cells

  16. Anaphase 2 • Sister chromatids separate and move towards the poles

  17. Telophase 2 • Nucleus reforms • Spindle fibers disappear • Cytokinesis • 4 NEW CELLS FORM WITH ½ THE ORIGINAL NUMBER OF CHROMOSOMES

  18. Meiosis 2 Meiosis II Telophase I and Cytokinesis I Metaphase II Anaphase II Telophase II and Cytokinesis Prophase II

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