Mitosis & meiosis


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  • Figure 13.5 The human life cycle
  • Mitosis & meiosis

    2. 2. Why can’t a cell keep on increasing in size?Cells MUST divide when their SA:V becomes small.
    3. 3. Cells divide : 1.For growth 2. To producegametes or spores 3.To replace damaged cells Salmon gametes mixingMucor
    4. 4. The nucleus contains thread- like structures called:
    5. 5. A nucleus can contain:
    6. 6. TWO types of cells in the body Non-reproductive Gametes or somatic cells (sex cells) diploid number haploid number of chromosomes spermsphagocyte Nerve cell
    7. 7. types of cell divisionproduces body cells produces sex cells
    8. 8. takes place in any part of a plant or animal which is producing new cells for growth or replacemente.g.bone marrow producing new blood cells
    9. 9. e.g.bone marrow producing new blood cells
    10. 10. e.g.skin cell productiongrowth of a muscle
    11. 11. Mitosis in buds Mitosis inshoot & root tips
    12. 12. occurs in reproductive organs and results in the formation of sex cells Meiosis forms the ovum and sperms in animals.
    13. 13. Key Haploid gametes (23) Haploid Where does Egg (23) Diploid meiosis occur in a male and a female human? Sperm (23) MEIOSIS FERTILISATIONOvary Testis Diploid zygote (46) Mitosis and Testes in development males & Multicellular diploid ovaries in adults (46) females
    14. 14. MALE FEMALESex organs Testes OvariesGametes Sperm Ovum / egg
    15. 15. MALE FEMALESex organs Anthers OvariesGametes Inside pollen Egg cell grains
    16. 16. Mark with an ‘X’ where meiosis occurs.
    17. 17. is called a REDUCTION-DIVISION. Why?as it causes the chromosome number to halve How is it possible to produce 4 cells by meiosis?
    18. 18. Mitosis or meiosis?
    19. 19. Which process restores the diploid number of chromosomes?
    20. 20. Meiosis reduces the chromosome number;Fertilisation restores the diploid number. 23 2346 46 meiosis egg 23 23 fertilisation46 sperm
    21. 21. Both occur in plants and animals.Both produce new cells as they are types of cell division.
    22. 22. TWO daughter cells
    23. 23. First division Second divisionFOUR daughter cells
    24. 24. Genetic variation isalmost infinite as a result of meiosis
    25. 25. First division Seconddivision NEW COMBINATIONS
    26. 26. 1. exchange of genetic material during meiosis2. random fertilisation
    27. 27. Random Fertilisation = even more variation A human ovum plus a human sperm - 1 of 8 million combinations possible for each ovum and sperm - 223 x 223 = over 70 trillion combinations  Any 2 parents will produce a zygote with over 70 trillion possible combinations without considering crossing over UNIQUE!!
    28. 28. Mitosis Meiosis1) Two cells are produced Four cells are produced2) Cells have the diploid Cells have the haploid number of chromosomes number of chromosomes3) One division occurs Two divisions occur4) Cells are genetically Cells are geneticallyidentical (CLONES) CLONES different5) Produces somatic cells Produces sex cells
    29. 29. 46 Write the 23 23 numbers ofchromosomes found in the cells shown. 46 46
    30. 30. are thread-like structures found in the nucleusthey only show up clearly at cell division as they shorten and thicken
    31. 31. Number of ChromosomesFruit Flies: 8 Carrots: 20 Dog: 48 Shrimp: 254 Adders tongue (Fern): 1260 Largest number of chromosomes
    32. 32. Fig. 4 Homologouschromosomes of a fruit fly.
    33. 33. 46 chromosomes in humans44 autosomes 2 sex chromosomes
    34. 34. Down’s Syndrome children have 47 chromosomes
    35. 35. The chance of having a Down syndrome child goes up with maternal age
    36. 36. A "good" egg from aEgg is in center of picture 32 year old woman.This is a low quality, eggfrom a woman 41 years old.Egg is irregularly shapedand dark.
    37. 37. A chromosome consists of DNA packed around proteins
    38. 38. The total extended length of DNA in a human cell is nearly 2m. Cheek cells
    39. 39. Carry information to make an individual
    40. 40. consists of two parallel strands linked together by weak hydrogen bondsit is twisted into a spiral
    41. 41. is a DOUBLE HELIX (a helix is any spiral- shaped object)
    42. 42. four different bases: A: adenine; T: thymine; C: cytosine; G: guanine
    43. 43. A always pairs with TC with Gthis is called complementary base pairing
    44. 44. is the basic unit of DNA
    45. 45. The diagram shows part of a DNA molecule. Complete thediagram by labelling the bases. T G G A
    46. 46. is a series of chemical structures called bases along the length of a chromosomeprovides ‘instructions’ to the cell, e.g. to make pepsin or the skin colour
    47. 47. is a spontaneous change in a gene or a chromosome which may produce a change in the characteristic under its controla mutation can be: harmful lethal beneficial (mutations in bacteria often produce resistance to drugs)
    48. 48. Naturally when chemicals on the DNA change position during nuclear divisionArtificially by means of mutagens
    49. 49.  an agent that causes a change in genetic composition
    50. 50. X-raysUV-rays
    51. 51. cigarette smokeasbestos
    52. 52. formaldehydepesticides
    53. 53. Question: MAY, 2004 (pg 78)It is not advisable for pregnant females to take X-rays because these can cause mutations in thedeveloping foetus. The X-rays can in fact act as amutagen (or mutagenic agent).ii)Explain the term mutation by referring to theDNA molecule. (2)A spontaneous change in the structure of DNA.A change in the sequence of bases occurs.
    54. 54. Question: pg 78ii) Name one human disease or condition which results from a mutation. (1)Haemophilia / Down’s syndromeiii)Name one mutagen other than X-rays. (1)UV rays
    55. 55. the information to build proteins
    56. 56. What are the building blocks of proteins called?
    57. 57. Name the bond between amino acids.
    58. 58. Fig.9 Protein synthesis inside a cell.
    59. 59. Fig.9 Protein synthesis inside a cell.
    60. 60. THE END