Meiosis (Reduction Division) I→PMATC→PMATC

1. Meiosis(Reduction Division)I→PMATC→PMATC

3. Mitosis Diagram In your journal, analyze then explain the significance of this diagram I→PMAT→C I→PMAT→C Pic 1 I→PMAT→C I→PMAT→C I→PMAT→C I→PMAT→C Pic 2 I→PMAT→C What is happening in pic 1? What is the result in pic 2?

4. Meiosis vs Mitosis Mitosis creates 2 identical daughter cells (diploid ) Meiosis creates 4 genetically different gametes (haploid)

5. Meiosis Introduction • Process of reductiondivision • Purpose: germ cells in the gonads produces gametes (sex cells) – sperm & egg • Meiosis is NOT A CYCLE like mitosis.

6. Diploid vs. Haploid • Diploid –a full set of homologous chromosomes (one from each parent) represented by the symbol 2N=46 • Found in somatic or body cells • Haploid – a cell that contains only a half set of chromosomes (one from each parent) represented by the symbol N or 1N • Found in gametes or sex cells – sperm & egg • N = 23

7. Meiosis IntroductionChromosome Numbers • Somatic cells: (diploid 2N = 46 chromosomes in humans) • Gametes: (haploid N = 23 chromosomes in humans) You DO NOThave to draw these pictures on the 1st tab for Meiosis Introduction Just write the Somatic and Gamete info above

8. Chromosome Numbers of Some Common Organisms

9. Meiosis Introduction • Similar to Mitosis’ IPMATC • Meiosis involves two distinct divisions, called Meiosis I and Meiosis II • By the end of Meiosis II, the 1 diploid cell that entered meiosis has become 4 haploid cells The next slide has a labeled picture for you to draw

10. Meiosis Introductionlabel the steps in your diagram using your book IPMATC→PMATC Interphase Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 & Cytokinesis Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 & Cytokinesis Meiosis 1 Meiosis 2

11. Interphase Centrioles • Stage between divisions • Contains: centrioles and chromatin • Chromosome structures have not formed yet • Made of stages: G1 – basic cell growthS – replication and repair of DNAG2 – final preparation for cell division Nucleus (with chromatin)

12. Meiosis I

13. Prophase I • homologous chromosomes from each parent pair up to form homologous pairs • Whenhomologous chromosome overlap its called crossing over. Centrioles Spindlefibers Homologous Pairs(Humans have 23 pairs making 46 total chromosomes)

14. Prophase I • Crossing over happens when parts of the homologues chromosomes switch places after overlapping

15. How can siblings look alike but not exactly the same if they come from the same parents?

16. Importance of crossing over • The gene combinations that a person gets from his or her parents will be different, to varying degrees, than the combination a sibling may get. • Crossing over increases genetic diversity IMPORTANT CONCEPT!!

17. More sibling similarities

18. Metaphase I Centrioles homologous pairs line up in the middle of the cell Spindlefibers Homologous Pairs

19. Anaphase I Centrioles • The homologous pairs separate • Sister chromatids don’t separate yet Spindlefibers Homologous Chromosomes

20. Anaphase I • If the chromosomes don’t separate correctly then a Nondisjunction will occur • THIS IS BAD • Example: downs syndrome 2N+1=47 Centrioles Spindlefibers Homologous Chromosomes

21. Important attributes of Meiosis I • “Crossing” over happens in prophase I • The homologous PAIRS separate in anaphase I which makes the daughter cells unique • The amount of DNA is still twice what it needs to be for a gamete...so we are not done yet! Meiosis I makes • 2 haploid (1n) cells that are genetically unique but the sister chromatids have not separated yet.

22. Anaphase Iif a Nondisjunction happens in Meiosis I • A Nondisjunction causes the gametes to have the wrong amount of chromosomes

23. Telophase I & Cytokinesis Centrioles • Telophase I – the cell creates a temporary nucleus around the chromosome sets • Cytokinesis – the cell divides into two cells Homologous Chromosomes Nuclear Membrane

24. Meiosis II • The two cells produced by meiosis I now enter a second meiotic division • The cells do NOT replicate DNA (no more interphase) • Each cell has half of the original DNA • 2N ÷ 2 = N

25. Prophase II • Similar to Prophase of Mitosis • Centrioles attach spindle fibers to the chromosomes Centrioles Spindlefibers Chromosomes

26. Metaphase II • Similar to Metaphase of Mitosis • chromosomes line up in the middle Centrioles Spindlefibers Chromosomes

27. Anaphase II Centrioles • Sister chromatids separate • Each chromatid is pulled to the opposite pole of the cell Chromatids Spindlefibers

28. Telophase II & Cytokinesis • Telophase II – the cells create a new nuclear membrane around the chromosomes • Cytokinesis – the cells divides into four haploid daughter cells Chromatids Nuclear Membrane

29. Important attributes of Meiosis II • The SISTER chromatids separate in anaphase II • This makes each new 1n cell unique • Meiosis II will result in gametes Meiosis II makes • 4 haploid (1n) cells that are genetically unique and contain ½ the DNA of the original 2n cell

30. Gamete (Sex Cell) Formation • In male animals (including humans), the haploid gametes produced by meiosis are called sperm • 4 sperm cells are produced from one meiotic division

31. Gamete (Sex Cell) Formation • In female animals (including humans), the haploid gametes produced by meiosis are called eggs • The cell divisions at the end of meiosis I & II are uneven, so that 1 large eggis produced along with3 other cells, called polar bodies, which are discarded and not involved in reproduction

32. Meiosis Animation • The following slide shows a simple animation using a cell with 2 pairs of homologous chromosomes going through meiosis.

34. Meiosis Animation Meiosis I Animation http://wps.prenhall.com/wps/media/objects/487/498728/CDA9_1/CDA9_1b/CDA9_1b.htm Meiosis II Animation http://wps.prenhall.com/wps/media/objects/487/498728/CDA9_1/CDA9_1c/CDA9_1c.htm

35. Vocabulary Reduction division– When the number of chromosomes per cell is cut in half Haploid – A cell that has half the amount of chromosomes. A cell that is “N” for chromosome amount Diploid – A cell that has twice the amount of chromosome. A cell that is “2N” for chromosome amount Germ Cell – cells found in the gonads that produce gametes (sperms & eggs) Gamete – the haploid “sex” cells (in animals they are sperm and egg cells) Somatic Cell – all diploid cells (body cells) that are not gametes Zygote – fertilized egg cell formed form the joining of the gametes (sperm and egg)

36. Vocabulary Centrioles – Organelles in the cell that help to move chromosomes during cell division Chromatin – What you call the DNA during Interphase, Very easy to access the genes for transcription and translation to create proteins Chromosome – What you call the DNA during the actual cell division stages (Pro-, Meta-, Ana-, and Telophase). Condensed/packed DNA for easy movement during cell division Chromatid – One of the “arms” of a chromosome ‘X’. Each chromatid is identical to the other because it is created by replication. A chromosome is made of two Sister Chromatids. Spindle Fiber – fibers created and used by the centrioles to move the chromosomes around during the division stages.

37. Vocabulary Homologous Chromosomes – the same numbered chromosome that pair up from mother and father (ex: mom’s chromosome 1 and dad’s chromosome 1) Crossing Over – A kind of chromosomal mutation that happens in Prophase 1 of meiosis. Homologous chromosomes overlap and exchange pieces of the chromosome which caused genetic variability. Nondisjuction – Happens in either Anaphase 1 or Anaphase 2 of meiosis when one centriole does not connect to the chromosome with a spindle fiber. Causes the gametes to have extra or missing chromosomes. Fertilization – The process of making a zygote. When egg and sperm cells fuse and combine their genetic information (DNA)

38. Comparing Mitosis to Meiosis

39. Comparing Mitosis to Meiosis

40. Use the following slides to complete the table.

41. Comparing Mitosis & Meiosis • Number of cells at beginning of process • Mitosis = 1 Diploid cell • Meiosis = 1 Diploid Cell • Number of cells at the end of the process • Mitosis = 2 Diploid Cells • Meiosis = 4 Haploid Cells

42. Comparing Mitosis & Meiosis • Number of chromosomes at the START • Mitosis- 46 (Diploid, “23 pairs, or set of two”) • Meiosis- 46 (Diploid, “23 pairs, or set of two”) • Number of chromosomes at the END • Mitosis- 46 (Diploid, “23 pairs, or set of two”) • Meiosis = 23 (Haploid, “23 singles, or set of 1/2”)

43. Comparing Mitosis & Meiosis • Is the genetic make-up of the daughter cells UNIQUE or IDENTICAL? • Mitosis produces 2 IDENTICAL CELLS • Meiosis produces 4UNIQUE CELLS

44. Comparing Mitosis & Meiosis • Type of cell in the human body that can undergo each phase • Mitosis produces SomaticBODY cells (skin) • Meiosis produces GameteSEX cells (sperm or eggs)

45. Comparing Mitosis & Meiosis • Purpose: • Mitosis creates cells for • Growth • Replacement • Repair • Asexual reproduction • Meiosis creates cells for • Sexual reproduction in humans and many other species

46. Interesting Facts • Females produce all their eggs at once, and store them at a very early age (They release one each month during mentration) • Males make sperm constantly from puberty until they die.