The document discusses cell reproduction through mitosis and meiosis. It provides details on: 1) The stages of the cell cycle including interphase and the phases of mitosis (prophase, metaphase, anaphase, telophase). 2) The key differences between mitosis, which produces identical daughter cells, and meiosis, which produces gametes with half the number of chromosomes. 3) The stages and outcomes of meiosis I and meiosis II, which reduce the chromosome number and lead to genetic diversity through independent assortment and crossing over.

1. CELL REPRODUCTION

2. Outline Types of Cell Division Structure of Chromosomes Cell Division in Prokaryotes Phases of cell cycle Interphase Mphase Cytokinesis Cell cycle-abnormalities

3. Cell Theory : all organisms consist of cells and arise from pre-existing cells Mitosis is the process by which new cells are generated for body tissues during development, growth, and tissue repair. 2 cells are produced in one cycle of division Daughter cells have ALL of the genetic material of the parent cell Meiosis is the process by which special cells called gametes are generated for reproduction. 4 cells are produced in two cycles of division Daughter cells have HALF the genetic material of the parent cell

4. SOMATIC Vs REPRODUCTIVE GAMETES (n) – EGGS (OVA) & SPERM - MEIOSIS (Somatic) OTHERS (2n) - MITOSIS NUCLEAR Vs CYTOPLASMIC DIVISION

5. The state in which there are two copies of each chromosome present is known as diploid (2n). H Haploid (n)– only one copy of a chromosome is present All of the somatic cells in our bodies are diploid cells The only cells in our bodies that are haploid are our gametes – eggs and sperm

6. Human somatic cells have 46 chromosomes diploid number (2n) = 46 23 from mom - 23 from dad 22 pairs are autosomes –true homologous pairs 1 pair is not necessarily homologous - sex chromosomes females are XX males are XY – a non homologous pair.

7. Meiosis – form of cell division where there are two successive rounds of cell division following DNA replication - produces haploid cells (n) - start with 46 double stranded chromosomes (2n) After 1 division - 23 double stranded chromosomes (n) After 2nd division - 23 single stranded chromosomes (n) - occurs in our germ cells – cells that produce our gametes - egg and sperm

8. Cell division Mitosis

9. Cell division All complex organisms originated from a single fertilized egg. Every cell in your body started here, through cell division the numbers are increased Cell then specialize and change into their various roles

10. Mitosis Mitosis is the process by which new body cell are produced for: Growth Replacing damaged or old cells. This is a complex process requiring different stages

11. Mitosis All daughter cells contain the same genetic information from the original parent cell from which it was copied. Every different type of cell in your body contains the same genes, but only some act to make the cells specialise – e.g. into nerve or muscle tissue.

12. BASIC GENETICS Each cell in the human body contains two sets of 2 3 chromosomes Mitosis identically replicates this information E ach cell therefore has the same genetic material Reproductive cells only have one set of chromosomes. These combine to make a new person with different genetic material to both parents

13. 2 daughter cells identical to original Parent cell Chromosomes are copied and double in number Chromosomes now split

14. Reproduction presents a major problem for cells and organisms: (how can information be transmitted faithfully to progeny) I II III IV = one bit of genetic information

15. = one bit of genetic information The information transfer problem becomes more challenging as more bits of information are incorporated into the organism

16. One of life’s solutions to this challenge: “Package” the bits of information into single units called chromosomes = one bit of genetic information

17. The nucleus Nuclear membrane - double membrane Chromosomes/Chromatin- genetic material/DNA Gene - DNA segment Chromosome---  DNA ---  Gene

18. chromosomes Packaging of genetic material in prokaryotes and eukaryotes prokaryote cell eukaryote cell

19. Structure of Chromosomes Chromosomes are composed of a complex of DNA and protein, chromatin. DNA exists as a single, long, double-stranded fiber extending chromosome’s entire length. forms nucleosome every 200 nucleotides DNA coiled around histone proteins

20. C Chromosome basics . T The number of chromosomes present within the nucleus is a characteristic of the species. Chromosomes of humans and most other eukaryotic species occurs in pairs. Members of a chromosome pair are known as homologues.

21. Mitosis/Cell division mitosis is the process of cell division in which one cell becomes two identical daughter cells development renewal regeneration

22. The cell cycle is the mechanism by which a cell duplicates its contents and then divides in two cell grows and duplicates its contents cell contents cell divides in two Each parental cell gives rise to two daughter cells on completion of each cell cycle parental cell daughter cell 1 daughter cell 2

23. Replication of chromosomes Replication is the process of duplicating a chromosome Occurs prior to division Replicated copies are called sister chromatids Held together at centromere

25. Binary Fission-prokaryotic cells

26. Cell Cycle

27. Prophase Metaphase Anaphase Telophase The Stages of M itosis Interphase

28. REMEMBER! I nterphase P rophase M etaphase A naphase T elophase (Individuals Please Make All The Cells) IPMAT

29. INTERPHASE After a cell has divided, the two new cells begin the process again, the cell s at this stage are in Interphase.

30. By late interphase, the chromosomes have been duplicated but are loosely packed. The centrosomes have been duplicated and begin to organize microtubules into an aster (“star”). Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

32. PROPHASE The chromatin (decondensed DNA) in the nucleus, condenses to form pairs of chromosomes . The centrioles move to opposite ends of the nucleus. As this is happening the nucleolus begins to break down Nuclear membrane begins to break down

33. Prophase Replicated chromosomes condense. Microtubules organize into a spindle

34. The Spindle A spindle is a web type structure made up of microtubule fibers. It is essential for mitosis because it arranges the chromosomes into their correct positions in preparation for cell division. Mitotic center Microtubule A cell at metaphase a spindle

35. Chromosomes attached to spindle during nuclear division

36. METAPHASE The spindle becomes fully developed The nuclear membrane has completely gone The chromatid pairs are aligned along the center of the spindle (the EQUATOR)

37. The spindle fibers push the sister chromatids until they are all arranged at the metaphase plate , an imaginary plane equidistant between the poles, defining metaphase. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

38. Anaphase Centromeres of sister chromatids separate Chromosomes move to opposite ends of the cell

39. At anaphase, the centromeres divide, separating the sister chromatids. Each is now pulled toward the pole to which it is attached by spindle fibers. By the end, the two poles have equivalent collections of chromosomes.

40. TELOPHASE Two new nuclei are formed when the chromosomes reach the opposite poles of the cell The nuclear membrane is formed- the nucleolus reappears The chromosomes disperse in the nucleus

41. Telophase Nuclear membranes form Spindle disappears Division of cytoplasm occurs (cytokinesis)

42. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

43. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

44. CYTOKINESIS Literally means, division of the cytoplasm M itosis is the splitting of the nucleus. Cytokinesis is the splitting of cytoplasm

45. Cytokinesis Cleavage of cell into two halves animal cells constriction belt of actin filaments plant cells cell plate

46. Cytokinesis Cytoplasmic division occurs after nuclear division is complete. Two cells are formed.

47. Cytokinesis in animals A cleavage furrow forms that pinches the cell in two - the furrow represents a ring of actin and myosin filaments just under the plasma membrane.

48. Rat – epithelial cells

49. Mitosis – bone cell slides 1 2 3 4 5 Parent cell Chromosomes copied Copies separating 2 daughter cells Cells split

50. Cytokinesis in plants A cell plate made up of cell-wall components gradually forms in the middle of the cell.

51. So what’s the difference in Plants? Plant cells do not have a centriole Plant cells do not pinch in half. Cytoplasmic division is accomplished by a cell plate forming between 2 daughter cells

52. Plants

53. Cell Turnover – The speed of mitosis One full cycle can vary between a couple of minutes to days. For example s kin and epithelial cells have a rapid turnover in the human body in order to replace the ones constantly being worn away. C ells which make up organs such as the eye and the brain, need not multiply as often once they reach adult size.

54. Organs which need to produce new cells continuously have the highest turnover . For example :- Bone marrow- producing replacement blood cells The testes - producing spermatogonia

55. Tumors Abnormalities can sometimes occur in c ells which reproduce at a rapid rate, this in turn may lead to the formation of tumors. Tumors of any type should be considered serious. Although benign tumors do n o t usually cause a threat to a persons life , they can cause great inconvenience if not treated.

56. CANCER uncontrolled cellular mitotic divisions

57. Meiosis

58. Meiosis – A Source of Distinction Why do you share some but not all characters of each parent? What are the rules of this sharing game? At one level, the answers lie in meiosis.

59. Meiosis does two things - 1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid). This is a good idea if you’re going to combine two cells to make a new organism. This trick is accomplished by halving chromosome number. In meiosis, one diploid cells produces four haploid cells.

60. Why do we need meiosis? Meiosis is necessary to halve the number of chromosomes going into the sex cells Why halve the chromosomes in gametes? At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents

61. 2) Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives. This makes for a lot of genetic diversity . This trick is accomplished through independent assortment and crossing-over . Genetic diversity is important for the evolution of populations and species .

62. Meiosis Parent cell – chromosome pair Chromosomes copied 1 st division - pairs split 2 nd division – produces 4 gamete cells with ½ the original no. of chromosomes

63. Meiosis – mouse testes Parent cell 4 gametes 1 st division 2 nd division

64. The Stages of Meiosis: aka: Reduction Division

65. Meiosis I : Separates Homologous Chromosomes Interphase Each of the chromosomes replicate The result is two genetically identical sister chromatids which remain attached at their centromeres

66. Prophase I During this phase each pair of chromatids match up with their homologous pair and fasten together (synapsis) in a group of four called a tetrad. Extremely IMPORTANT!!! It is during this phase that crossing over can occur. Crossing Over is the exchange of segments during synapsis.

67. Metaphase I The chromosomes line up at the equator attached by their centromeres to spindle fibers from centrioles. Still in homologous pairs

68. Anaphase I The spindle guides the movement of the chromosomes toward the poles Sister chromatids remain attached Move as a unit towards the same pole The homologous chromosome moves toward the opposite pole Contrasts mitosis – chromosomes appear as individuals instead of pairs (meiosis)

69. Telophase I This is the end of the first meiotic cell division. The cytoplasm divides, forming two new daughter cells. Each of the newly formed cells has half the number of the parent cell’s chromosomes, but each chromosome is ready for the second meiotic cell division

70. Cytokinesis Occurs simultaneously with telophase I Forms 2 daughter cells Plant cells – cell plate Animal cells – cleavage furrows NO FURTHER REPLICATION OF GENETIC MATERIAL PRIOR TO THE SECOND DIVISION OF MEIOSIS

71. Figure 13.7 The stages of meiotic cell division: Meiosis I

72. Meiosis II : Separates sister chromatids Similar to mitosis THERE IS NO INTERPHASE II !

73. Prophase II Each of the daughter cells forms a spindle, and the double stranded chromosomes move toward the equator

74. Metaphase II The chromosomes are positioned on the metaphase plate in a mitosis-like fashion

75. Anaphase II The centromeres of sister chromatids finally separate The sister chromatids of each pair move toward opposite poles Now individual chromosomes

76. Telophase II and Cytokinesis Nuclei form at opposite poles of the cell and cytokinesis occurs After completion of cytokinesis there are four daughter cells All are haploid (n)

77. Figure 13.7 The stages of meiotic cell division: Meiosis II

78. One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment Independent assortment produces 2 n distinct gametes, where n = the number of unique chromosomes. That’s a lot of diversity by this mechanism alone. In humans, n = 23 and 2 23 = 6,000,0000.

80. Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.

81. Mitosis vs. Meiosis

82. The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis Mitosis The first (and distinguishing) division of meiosis

83. Mitosis vs. Meiosis

84. Boy or Girl? The Y Chromosome “Decides” X chromosome Y chromosome

85. Boy or Girl? The Y Chromosome “Decides”

86. Meiosis – division error Chromosome pair

87. Meiosis error - fertilization Should the gamete with the chromosome pair be fertilized then the offspring will not be ‘normal’. In humans this often occurs with the 21 st pair – producing a child with Downs Syndrome

88. 21 trisomy – Downs Syndrome Can you see the extra 21 st chromosome? Is this person male or female?