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Topic 4.2 & 10.1 Notes

Topic 4.2 & 10.1 Notes. Meiosis. A reduction in chromosomes to form HAPLOID cells. 2N to 1N. Homologous pairs . They associate with each other during prophase 1 through synapsis. Chromosomes replicate in which phase?. S phase!. Prophase 1.

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Topic 4.2 & 10.1 Notes

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  1. Topic 4.2 & 10.1 Notes

  2. Meiosis • A reduction in chromosomes to form HAPLOID cells. • 2N to 1N

  3. Homologous pairs • They associate with each other during prophase 1 through synapsis.

  4. Chromosomes replicate in which phase? • S phase!

  5. Prophase 1 • The homologous chromosomes form BIVALENTS. These are replicated homologous chromosomes. • The sister chromatids are next to each other, joined at the centromere.

  6. Crossing Over • Non sister chromatids may cross over during prophase 1 leading to recombinant alleles.

  7. More detail on Prophase 1 Synapsis-the chromosomes associate Crossing Over-The Chiasma are the points at which they cross over. A Holliday junction forms when they anneal. This increases genetic diversity!

  8. Metaphase 1 • Bivalents line up at the equator double file. • There are many positions that they can align themselves in. • This adds to the genetic variation…more on this later!

  9. Anaphase 1 • This is where the reduction takes place. The pairs separate, but the sister chromatids remain attached!

  10. Non Disjunction

  11. Telophase 1 • The cells are no longer diploid here. • The chromosomes may not be exact matches of each other due to crossing over.

  12. Cytokinesis 1

  13. Prophase II • The nuclei break down again, but the chromosomes do not cross over again.

  14. Metaphase II • Random orientation again contributes to variation in gametes.

  15. Anaphase II • Chromatids are pulled to the opposite poles.

  16. Telophase II and Cytokinesis

  17. Oogenesis

  18. Spermatogenesis

  19. Mendel and Independent Assortment • The presence of an allele of one of the genes in a gamete has no influence over which allele of another gene is present. • This is only true for unlinked genes. • Click here for a more detailed explanation.

  20. HOMEWORK 4.2/10.1 • Make a T Chart to compare/contrast mitosis and meiosis. • Please include as many as possible, but a minimum of 6. • You may need to do some research ON YOUR OWN. • Due Friday

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