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Mitosis and Meiosis

Mitosis and Meiosis. Chromosomes made of DNA wrapped around histone protein (beads) to make nucleosomes. Chromatin - mixture of DNA and protein that makes up chromosome Chromosomes make possible the precise separation of DNA during cell division. Chromosome parts Telomere - end

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Mitosis and Meiosis

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  1. Mitosis and Meiosis

  2. Chromosomes made of DNA wrapped around histone protein (beads) to make nucleosomes

  3. Chromatin - mixture of DNA and protein that makes up chromosome • Chromosomes make possible the precise separation of DNA during cell division

  4. Chromosome parts Telomere - end Centromere - middle Arms - chromatids

  5. Cell Cycle - series of events in the growth and division of a cell

  6. Interphase (‘in between’) • 1) cell grows (G1) • 2) DNA duplicates (S) • 3) Cell produces organelles for division (G2) Basically, the cell is growing and getting ready for division

  7. Chromosomes duplicate themselves during normal cell lifetime (interphase)

  8. Before chromosome duplication (replication) • Called diploid (2N) because you have one chromosome from each parent

  9. After interphase - cells have 2 sets of each chromosome from mom and dad (4N)

  10. Mitosis - cell division starts in the nucleus • Stages: • Prophase • Metaphase • Anaphase • Telophase

  11. 1) Prophase - DNA condenses, spindle starts to form

  12. 2) Metaphase - duplicated chromosomes line up, spindles connect to centromeres

  13. 3) Anaphase - sister chromatids separate and move toward centrioles (where spindles originate)

  14. 4) Telophase - chromosomes unwind and nuclear envelope forms

  15. Stop day 1

  16. Cytokinesis - final splitting of one cell into two Animal cells - cell membrane is pinched inward

  17. Plant cell cytokinesis- membrane too rigid to move due to cell wall - so a plate forms halfway between 2 new nuclei

  18. Stop Day 2

  19. Meiosis • Cell division to produce gametes (sex cells)

  20. Ploidy - number of sets a chromosome in a cell nucleus • Notice these chromosomes are not duplicated

  21. Homologous (ho - mahl-a-gus) - chromosomes carry same genes (but one from mom, one from dad)

  22. Before replication - one homologous set for each chromosome

  23. After replication - two homologous sets of each chromosome (4N)

  24. Meiosis - can be broken into Meiosis I and Meiosis II • Before Meiosis I, chromosomes replicate • Before Meiosis II, chromosomes do not replicate

  25. Meiosis I (steps) • 1) Chromosomes duplicate (interphase)

  26. Blue = from Dad, Pink = from Mom

  27. Human chromosomes before replication (2N)

  28. Human chromosomes after duplication (4N)

  29. Step 2) Prophase I- paired homologous chromosomes form tetrads • Crossing over - homologous chromosomes exchange alleles! Crossing over creates new Combinations of alleles In daughter cell (shuffles genetics)

  30. Tetrad - two copied homologous chromosomes

  31. Step 3) Metaphase I - paired homologous chromosomes line up in center of the cell and are pulled apart

  32. Step 4) Anaphase I - spindle fibers pull each homologous pair towards opposite ends

  33. Step 5) Telophase I - nuclear membranes form, then cytokinesis occurs

  34. Meiosis I vs. Mitosis • Daughter cells in meiosis I do not have identical chromosomes as parent cell • 2 daughters are haploid because during division, each daughter gets one half of the homologous pair • Crossing over makes it so each daughter cell doesn’t just have chromosome from one parent

  35. Meiosis II • Difference: chromosomes do not replicate before this division

  36. Meiosis II • In meiosis II, the two daughter cells from meiosis I split back into separate chromatids (go haploid)

  37. Meiosis II produces 4 haploid gametes. (sperm, egg) These cells are incomplete and need to be paired with an opposite gamete to have full genetic information.

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