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Meiosis: The reason why we are all unique

Meiosis: The reason why we are all unique. Meiosis occurs in two main phases Meiosis I Meiosis II. Meiosis: The reason why we are all unique. Big Ideas: The number of chromosomes per cell is cut in half from diploid to haploid Crossing over creates new combinations of alleles

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Meiosis: The reason why we are all unique

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  1. Meiosis:The reason why we are all unique Meiosis occurs in two main phases Meiosis I Meiosis II

  2. Meiosis:The reason why we are all unique Big Ideas: The number of chromosomes per cell is cut in half from diploid to haploid Crossing over creates new combinations of alleles Meiosis I results in 2 daughter cells with new allele pairings Meiosis II results in 4 haploid gametes (with half the number of chromosomes) Haploid gametes merge (fertilization) to create a diploid zygote

  3. The phases of meiosis – MEIOSIS I • Interphase - Chromosomes in diploid cells replicate to make sister chromatids.

  4. The phases of meiosis – MEIOSIS I • Prophase I -Replicated chromosomes pair up with corresponding chromosomes and form a TETRAD • Chromatids of homologous chromosomes literally cross over • The crossed sections (which contain alleles) are exchanged - Crossing over creates new combinations of alleles.

  5. The phases of meiosis – MEIOSIS I • Metaphase I and Anaphase I • Paired homologous chromosomes line up on the metaphase plate • Each homologous chromosome pair is pulled to opposite sides of the cell.

  6. The phases of meiosis – MEIOSIS I • Telophase I and Cytokinesis • Nuclear envelope reforms around each cluster of chromosomes • Cell membrane pinches the cytoplasm creating two new daughter cells • When cytokinesis in complete, there are two haploid daughter cells that are genetically different.

  7. The phases of meiosis – MEIOSIS II • Prophase II • Chromosomes become visible in both diploid daughter cells • NO Tetrads because homologous pairs have already separated

  8. The phases of meiosis – MEIOSIS II • Metaphase II Chromosomes line up in the center • Anaphase II Spindle fibers pull paired chromatids apart • Telophase II Nuclear envelope reforms • Cytokinesis 4 haploid daughter cells are formed

  9. The phases of meiosis – MEIOSIS II

  10. The phases of meiosis – MEIOSIS II What do you notice about the chromosomes in the 4 haploid daughter cells? 2. Go back to slide 4 (Prophase I). What are the genotypes of the chromosomes in the tetrad? What are the genotypes of the 4 gametes? 3. Why do you think meiosis is described as the reason why we are all unique?

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