Chromosome Structure and Cell Division

1. Chapter 8: Cell Reproduction Section 1: Chromosomes Section 2: Cell Division Section 3: Meiosis

2. What are chromosomes? • Rod shaped structures inside the nucleus of Eukaryotic cells • Made of DNA and proteins • Contain the genes that make you, you! • Shape of the chromosome is maintained by histones

4. Chromosome Structure • 3 forms of a chromosome • Chromatin – ball of yarn • Chromatid – half of an x, sometimes bent • Chromosome – X • Center of X is called a centromere

5. Chromosome Types • Sex Chromosomes • Determine the sex of the organism • Males XY • Females XX • 2 out of 46 in the human cell • Autosomes • All the other chromosomes • 44 out of 46 in the human cell

6. Section 1 Chromosomes Chapter 8 Sex Chromosomes and Autosomes Click below to watch the Visual Concept. Visual Concept

7. What are Homologous Chromosomes? • Also called homologues • 2 copies of the chromosome • One from Mom; One from Dad • Have the same size • Have the same shape • Have the same information (genes)

8. Two Types of Cells • Diploid • Cells that have chromosomes in pairs • Symbol 2n • Somatic cells or body cells are like this • Humans diploid number is 46. • Haploid • Cells that do not have chromosomes in pairs • Symbol 1n • Gametes are like this • Sex cells • Sperm and egg cells • Humans haploid number is 23.

9. Section 2 Cell Division Chapter 8 Cell Division in Prokaryotes, continued • Binary fissionis the process of cell division in prokaryotes.

10. Section 2

11. Two types of Reproduction • Asexual Reproduction • Production of offspring from one parent • Mitosis • Sexual Reproduction • Production of offspring from 2 parents • Meiosis

12. How do little elephants grow up to be BIG elephants?

13. Why do animals shed their skin?

14. The process of asexual reproduction begins after a sperm fertilizes an egg.

15. Three reasons why cells reproduce by asexual reproduction: 1. Growth 2. Repair 3. Replacement Skin cancer - the abnormal growth of skin cells - most often develops on skin exposed to the sun. Cell that reproduce by asexual reproduction reproduce constantly.

16. Animated Mitosis Cycle http://www.cellsalive.com/mitosis.htm • Interphase • Prophase • Metaphase • Anaphase • Telophase & Cytokinesis

17. Interphaseoccurs before mitosis begins • 3 phases • G1 – cell is growing • S – DNA is being copied • G2 – cell is preparing for mitosis Nuclear Membrane And nucleolus are visible CHROMATIN! CELL MEMBRANE Nucleus Cytoplasm

18. Interphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

19. Nuclear membrane & nucleolus disappear by end of prophase Prophase 1st step in Mitosis • Mitosis begins (cell begins to divide) • Chromosomes are visible • Centrioles(or poles) appear and begin to move to opposite end of the cell. • Spindle fibers form between the poles. Centrioles Sister chromatids Spindle fibers

20. Prophase Plant Cell Animal Cell Spindle fibers Centrioles Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

21. Metaphase 2nd step in Mitosis • Chromosomes attach to the spindle fibers at the centromere CHROMOSOME Centrioles Spindle fibers

22. Metaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

23. Anaphase 3rdstep in Mitosis • Chromatids (or pairs of chromosomes) separate and begin to move to opposite ends of the cell. Centrioles Spindle fibers

24. Anaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

25. Nuclear membrane & nucleolus are visible by end of telophase Telophase4th step in Mitosis • Two new nuclei form. • Chromosomes appear as chromatin (threads rather than rods). • Mitosis ends. Overlaps with cytokinesis! Nuclei Nuclei Chromatin

26. Telophase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

27. Cytokinesisoccurs after mitosis • Division of the cytoplasm • Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes. • Animal cells – form a cleavage furrow • Plant cells – form a cell plate, which becomes the cell wall.

29. Animal Mitosis -- Review

30. Plant Mitosis -- Review

31. IPMATC REMEMBER! • Interphase • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis IPrayMore AtThe Church

32. Cell Cycle

34. MitosisAnimation http://www.cellsalive.com/mitosis.htm

35. Section 2 Cell Division Chapter 8 Control of Cell Division • Cell division in eukaryotes is controlled by many proteins. • Control occurs at three main checkpoints. • G1 checkpoint – check to see whether the cell is healthy and is large enough to divide • G2 checkpoint – check to make sure DNA is copied correctly • Mitosis checkpoint – if cell divided correctly, then signals are made to exit mitosis

36. Section 2 Cell Division Chapter 8 Control of the Cell Cycle Click below to watch the Visual Concept. Visual Concept

37. Section 2 Cell Division Chapter 8 Control of Cell Division, continued • When Control is Lost: Cancer • Cancer is uncontrolled growth of cells • Cancer may result if cells do not respond to control mechanisms. • Can be caused by mutations in DNA

38. Section 3 Meiosis Chapter 8 Formation of Haploid Cells • Meiosisis a process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell. • Start with 46 and end with 23 • Meiosis leads to four haploid cells (gametes) rather than two diploid cells as in mitosis. • Done by germ cells • Meiosis produces haploid gametes. • Is considered sexual reproduction • Creates genetic diversity • Two divisions

39. Section 3 Meiosis Chapter 8 Meiosis I • Meiosis I includes prophase I, metaphase I, anaphase I, and telophase I. • Crossing-over, which is when portions of homologous chromosomes exchange genetics material, occurs during prophase I and results in genetic recombination.

40. Prophase I • Homologous chromosomes (paired chromosomes) become visible • Nuclear membrane and nucleolus disappear • Spindle fiber starts to appear • Crossing over occurs – portions of the chromatid break off and attach to other homologous chromosome

41. Section 3 Meiosis Chapter 8 Tetrads and Crossing-over of Genetic Material Click below to watch the Visual Concept. Visual Concept

42. Metaphase 1 • Homologous chromosomes (tetrads) line up at the equator and connect to spindle fibers at their centromeres

43. Anaphase 1 • Homologous chromosomes split and individual chromosomes move to poles • They assort independently of one another- independent assortment

44. Telophase 1and Cytokinesis 1 • There are 2 new cells at this point • Each new cell has half the number of chromosomes as the parent germ cell • So they are now haploid

45. Meiosis 2 • Has prophase II, metaphase II, anaphase II and telophase II • Exactly like mitosis • Four new haploid cells result • Four gametes • Depends on whether it is an animal or a plant cell

46. Section 3 Meiosis Chapter 8

47. Gametogenesis – making of gametes • Spermatogenesis • Making of sperm cells • Meiosis will result in 4 mature sperm cells or spermatozoa • Oogenesis • Making of mature egg cells, or ova • Meiosis will result in 1 mature egg cell and 3 polar bodies that die