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Meiosis: going from diploid to haploid

Meiosis: going from diploid to haploid

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Meiosis: going from diploid to haploid

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  1. Meiosis:going from diploid to haploid Making Gametes: Egg and Sperm

  2. The cell cycle remains the same except… G1 Division: meiosis& cytokinesis S G2

  3. Meiosis Overview • Process of nuclear division that reduces the number of chromosomes in new cells to HALF the number in the original cell. • Diploid  Haploid

  4. MEIOSIS • Before Meiosis I happens, the cell will go through interphase: • G1, S, G2 (just like Mitosis) MEIOSIS I • Prophase I (crossing over) • Metaphase I • Anaphase I (homologous chromosomes separate) • Telophase I and cytokinesis

  5. Homologous Chromosomes • Both chromosomes have the same traits but different versions of those traits • Paired chromosomes that encode for different versions of the same trait are called homologous chromosomes

  6. Haploid vs. Diploid

  7. Haploid vs. Diploid

  8. Prophase I • Prophase I is the longest and most complex phase. • All of the events that occurred during prophase of mitosis occur + • Homologous chromosomes come together to form a SYNAPSE (TETRAD). • CROSSING-OVER occurs.

  9. Crossing Over Crossing Over: Portions of chromatids break off and attach to adjacent chromatids on the homologous chromosome This allows for more genetic variability! We don’t want everyone to look the same. • Occurs during Prophase I

  10. Metaphase I • Homologous chromosomes line up randomly at the center of the cell. We call this independent assortment.

  11. Instead of all the chromosomes lining up in Metaphase in a single-file line, they will pair up with their homologous partner Meiosis Mitosis

  12. Anaphase I • During anaphase the homologous chromosomes in the center of the cell divide.

  13. Telophase I / Cytokinesis • Telophase I two nuclei form (23 duplicated chromosomes in each) • Cytokinesis occurs resulting in 2 haploid daughter cells.

  14. Meiosis I Interphase Prophase I Metaphase I Anaphase I Telophase I Cytokinesis Images from:

  15. Diploid  Haploid

  16. Colorful Karyotypes • Color the replicated chromosomes from your parents • Maternal – mother • Paternal – father! • Remember: your parents received one copy of each chromosome from their parents

  17. Time to figure out your chromosomes! • Flip a coin 22 times • If heads, fill in color A • If tails, fill in color B • If you are a girl: In the box draw and color in an X to match your dad’s X • If you are a boy: daw and color in a Y to match your dad’s Y • Repeat for the egg: heads – C, tails – D • Boy and girls both receive an X from mom (flip a coin to determine C or D)

  18. Fill in your karyotype!! Use the colors from the sperm and egg diagrams Chromosomes form after egg and sperm unite and chromosomes replicate Left chromosome – paternal colors Right chromosome – maternal colors Don’t forget the XX or XY chromosomes!

  19. Tips for a Better Movie • Don’t spend time arguing about what colors to use, but rather focus on making your first cell model and then modify it according to your drawings. • TRY and KEEP CAMERA and ZOOM in the same spot/position/angle as you take each picture. • While one of you gets ready to take a picture, the other team member gets going in moving the parts of the cell. • Be mindful of what else is in the frame to avoid things popping in and out of your video. • Take more pictures than you need. Experiment if flash or no flash works better. • Have fun and be creative! • DON’T FORGET YOUR ID TAG!!!!!!

  20. Meiosis II • Meiosis II comes directly after cytokinesis. No growth (interphase) takes place. • The steps of Meiosis II are identical to mitosis. • DNA is NOT duplicated before Meiosis II

  21. Prophase II • Chromatin condenses into chromosomes • Nuclear envelope breaks down

  22. Metaphase II • Duplicated chromosomes line up in the middle of the cell • Spindle fibers from the centrioles attach to each sister chromatid

  23. Anaphase II • Sister chromatids separate.

  24. Telophase II • Telophase II is the same as telophase in mitosis. • At the end of the second Cytokinesis in Meiosis there are 4 haploid cells • Males: 4 sperm • Females: 1 egg + 3 polar bodies Spermatogenesis Oocyte (oogenesis)

  25. Meiosis II Coming from Meiosis I Prophase II Metaphase II Telophase II Anaphase II Cytokinesis Images from:

  26. Meiosis I Interphase Prophase I Metaphase I Anaphase I Telophase I Cytokinesis Images from:

  27. Meiosis II Coming from Meiosis I Prophase II Metaphase II Telophase II Anaphase II Cytokinesis Images from:

  28. Haploid  Haploid

  29. Summary of Meiosis Meiosis I = separates homologous chromosomes Meiosis II = separates sister chromatids

  30. What is the goal of meiosis? • Meiosis 1 • Goal – reduce the chromosome number & mix up the DNA • Meiosis 2 • Goal – separate sister chromatids and form 4 cells

  31. Sexual Reproduction • Involves the fusion of two separate parent cells. • Offspring produced by sexual reproduction inherit some of the genetic information from each parent

  32. Chromosome Mutations • Deletion: entire gene lost • Insertion: entire gene added • Duplication: gene is repeated • Translocation: rearrangement of genes between non-homologus chromosomes • Inversion: segment of gene is reversed

  33. ERROR, ERROR, ERROR • Non- Disjunction • Sister chromatids fail to separate properly during meiosis II • Failure of a chromosome to separate from its homologue during meiosis • One gamete receives an extra copy of a chromosome and the other gamete lacks the chromosome entirely

  34. Escape Room • With a partner, find and answer all the questions • Go to • Use the answer to solve the puzzles for the final code to escape the room

  35. Choice • Mitosis Worksheet • Phases of Meiosis Worksheet • I Have Who Has Review Cards • Mitosis Taboo • Quizlet – cell cycle