1. Chapter 8 Cell Reproduction

2. When a cell divides, its DNA coils into small packages, the chromosomes. The chromosomes consist of DNA and protein histone molecules. Histones maintain shape and allow for compact storage of DNA.

3. Typical Chromosome

4. Histone Proteins & DNA Histone proteins allow DNA to coil and to be stored away much easier. The DNA can coil and uncoil as needed.

5. Chromatin When a cell is not dividing, the parts of the DNA that need to be used uncoil, the less tightly coiled form is chromatin.

6. Chromosomes, Chromatids & Centromeres. In a dividing cell, the chromosomes have two identical halves, the sister chromatids. The two chromatids are attached at the centromere.

7. Prokaryotic Chromosomes Single prokaryotic chromosomes are found in the cytoplasm, not bound by a nuclear membrane, and often attached to the cell membrane.

8. Species and Chromosome Number Each species has a characteristic number of chromosomes: Adder’s tongue fern1262 Cat32 Chimpanzee48 Dog78 Human46 Lettuce18 Orangutan48

9. Chromosomes are either: 1. sex chromosomes 2. autosomes

10. Human Sex Chromosomes Humans have one pair of chromosomes that determines the sex of the individual. (When it is said that one pair determines the sex remember this means 2 chromosomes out of the total of 46 chromosomes. That means there are 44 other chromosomes.)

11. Sex Determination in Humans Sex chromosomes determine the sex of the organism. Human sex chromosomes are either "X" or "Y.“ Sex is determined by which pair of sex chromosomes is received from parents.

12. Autosomes All the other chromosomes in an organism are the autosomes. Humans have 2 sex chromosomes and 44 autosomes for a total of 46.

13. Homologous Chromosomes Every cell, excluding sex cells, has 2 copies of each chromosome. 1 copy from each parent. The two copies of each autosome are called homologous chromosomes. Homologues are the same size and shape and carry genes for the same traits.

15. Karyotypes A karyotype is a photomicrograph of the chromosomes in a dividing cell. Karyotypes are used to examine an individual's chromosomes. The chromosomes are photographed, cut out, and arranged by size and shape into pairs.

16. Normal Human Karyotype

17. Human Karyotype Lab Some human diseases are caused by additional, missing, or damaged chromosomes. Karyotypes are used observe the chromosomes themselves. Cell division is stopped at metaphase and a picture of the chromosomes is made.

18. Diploid vs. Haploid Cells with two autosomes for each homologous pair are diploid. Diploid cells also have two sex chromosomes.

19. Diploid is abbreviated as 2n. In humans, the 2n number is 46.

20. Sperm and egg cells are haploid, containing only one set of chromosomes. They have only one autosome and one sex chromosome from each pair.

21. Haploid is abbreviated 1n. In humans, the 1n number is 23.

22. Sperm Cell Egg Cell

23. When a 1n sperm cell unites with a 1n egg cell, a 2n new organism results. (If reproductive cells were 2n, there would be too many chromosomes and the fertilized egg cell would be nonfunctional.)

24. Fertilization of a Human Egg Cell

25. Cell Division Humans produce about 25 million new cells per second (about 2 trillion new cells per day) and all cells come from preexisting cells.

26. Cell Division in Prokaryotes Binary fission is the mode of cell division in prokaryotes

27. Binary Fission Steps: 1. Binary Fission begins. 2 DNA is copied. 3. The cell grows to twice its original size. 4. The membrane pinches inward between the DNA copies, a new cell wall forms.

28. Cell Division in Eukaryotes 2 kinds of eukaryotic cell division: Mitosis Meiosis

29. Mitosis One cell splits to form two identical cells as in growth, repair, or asexual reproduction.

31. Meiosis Occurs during the formation of gametes (sperm and egg cells). The number of chromosomes is reduced by 1/2.

33. The Cell Cycle The Cell Cycle is the set of repeating events during the life span of a cell. Cell division is only part of the cell cycle. The time between one cell division and the next is interphase. Interphase is divided into three phases and cell division is divided into two phases.

34. The Cell Cycle (picture)

35. Mitosis & Cytokinesis Cell division consists of mitosis and cytokinesis. MITOSIS is division of the nucleus. CYTOKINESIS is division of the cytoplasm.

36. The Phases of Mitosis 1.Prophase 2.Metaphase 3.Anaphase 4.Telophase

37. Interphase Interphase begins the cell cycle. Cells spend most of their time in interphase. Cells are about 1/2 of their normal size at the beginning.

38. The three sub phases of Interphase G 1 – the cell grows to its mature size G 0 – the cell cycle stops S - the DNA is synthesized (copied) G 2 – the cell makes final preparations for cell division

39. G 1 – Growth Phase 1 G 1 begins immediately after cytokinesis. During this period, cells grow to their full size, new organelles are produced, and the cell carries out normal activities.

40. G0G0 G 0 cells reach mature size at the end of G 1 and then stop their cell cycle. They do not copy their DNA nor do they prepare for cell division. Example: Central Nervous System cells.

42. S - Synthesis During the S phase of interphase, DNA is synthesized. An exact copy of the DNA is made to be used in the new cell that will be formed.

44. G 2 - Growth Phase 2 During G 2, the cell prepares for cell division. Organelles and cellular structures are duplicated. Structures begin to move to the places they need to be in cell division.

45. Prophase Prophase begins mitosis. DNA condenses to chromosomes. These are actually double chromosomes attached at a centromere. The nuclear envelope begins to disassemble and disappear.

46. Centrosomes appear next to the nucleus. Spindle fibers form between the centrosomes as they move toward the poles. 2 types of spindle fibers Kinetochore fibers Polar fibers

49. Metaphase 2nd phase of mitosis. Chromosomes are easy to identify. It is at this stage that most images for karyotypes are taken. Chromosomes are attached to kinetochore fibers that move them to the equator of the cell.

51. Metaphase

52. Anaphase Chromatids separate at the centromere. Chromatids are slowly pulled toward the poles. The centromeres lead the way. This produces a classic “A” or “V” shape to the chromosome. Once the chromatids separate, they are considered to be individual chromosomes.

55. Telophase Telophase begins when the chromosomes reach the poles. The spindle fibers disassemble (they are made of proteins.). The chromosomes begin to uncoil back to their chromatin form. The nuclear membrane and the nucleolus reappear in each new cell.

58. Cytokinesis Cytokinesis is the division of the cytoplasm. Begins with an inward pinching of the cell membrane midway between the two new nuclei. The area that pinches inward forms the cleavage furrow.

62. The microfilaments in the cleavage furrow eventually pinch the cells into two new cells.

64. Cytokinesis in Plants Cytokinesis also occurs in plant cells as they divide. Vesicles from the Golgi join together at the midline and form a new piece of cell wall that separates the new cells.

68. Control of Cell Division Proteins regulate the cell cycle. Controls occur at 3 main checkpoints: 1. Cell Growth (G1) checkpoint 2. DNA Synthesis (G2) checkpoint 3. Mitosis checkpoint

69. Cell Growth G 1 Checkpoint If the cell is healthy and full size, proteins will start DNA synthesis. Proteins can stop cell division at this point if: conditions are not good for DNA synthesis the cell needs a rest the cell goes to G 0 the cell has not grown to full size

70. DNA Synthesis G2 Checkpoint DNA replication is checked by proteins for mistakes. If no mistakes are found, mitosis begins.

71. Mitosis Checkpoint Proteins check mitosis and signal the cell to enter G 1 if all the events of mitosis occurred correctly.

72. Loss of Control of Cell Division: CANCER If a mutated gene produces a regulatory protein, the protein may not work correctly. Cell growth and division may be abnormal with the mutated protein. This condition may lead to cancer (uncontrolled cell growth).

73. Cancer cells do not respond to the normal control mechanisms. Some cancers overproduce cells. Some cancers interfere with proteins that slow or stop the cell cycle.

74. Overproduction of Cells

75. Meiosis Meiosis is a nuclear division process that reduces the number of chromosomes to one half the number of the original cell.

76. Meiosis produces sex cells: Male: sperm cells Female: egg cells

77. In humans, sperm and egg cells each contain 23 chromosomes (1n). When sperm and egg cells fuse, a zygote with 46 chromosomes (2n) results.

78. Zygotes

79. Meiosis I Cells beginning to go through meiosis enter the G 1, S, and G 2 phases and divide through an initial cell division called Meiosis I.

80. Meiosis II Meiosis II is a second cell division in which the DNA is not copied. The 2 cells that go through this division form four haploid (1n) cells.

82. Major Events of Meiosis I Phases of meiosis I: Prophase I Metaphase I Anaphase I Telophase I Cytokinesis I

83. Prophase I DNA coils into chromosomes. Spindle fibers appear. The nuclear membrane and nucleolus disappear.

84. Homologous chromosomes pair during synapsis. Tetrads form and crossing over occurs.

85. Crossing Over Portions of chromatids break off and exchange places with corresponding portions of adjacent chromosomes. This process allows for the exchange of material between maternal and paternal chromosomes resulting in a new mixture of the genetic material.

86. Crossing over

87. Metaphase I The tetrads line up along the equator of the cell. The orientation of the tetrad is random. Spindle fibers from one pole attach to the centromere of one homologous pair and fibers from the opposite pole attach to the centromere of the other homologous pair.

89. Anaphase I The pairs of homologous chromosomes consisting of two chromatids joined by a centromere each move to opposite poles of the cell. This is called independent assortment and it results in greater genetic variation.

91. Telophase I / Cytokinesis I The chromosomes reach the opposite poles of the cell and cytokinesis begins. At this time, the cells contain the haploid number of chromosomes, but each new cell contains two copies of each chromosome as chromatids.

93. Meiosis II Meiosis II occurs in the cells formed during Meiosis I. The events of meiosis II are NOT preceded by DNA synthesis.

95. Prophase II The chromosomes remain in their tightly coiled chromosome form. Spindle fibers begin to move the chromosomes to the middle of the cell.

96. Metaphase II The chromosomes align along the equator of the cell. The chromatids randomly face one of the two poles.

97. Anaphase II The chromatids separate and move toward the opposite poles.

98. Telophase II The nuclear membrane reforms around the nucleus of each new cell.

99. Cytokinesis II The cytoplasm divides resulting in 4 new cells each with half of the cell’s original number of chromosomes.

100. Spermatogenesis / Oogenesis Gametes are the only cells in humans that divide by meiosis. Meiosis occurs: In the testes of males. In the ovaries of females.

101. Spermatogenesis Spermatogenesis occurs in the testes and results in the production of immature spermatids. Spermatids eventually develop into mature spermatozoa. For every cell that enters spermatogenesis, four healthy functioning spermatozoa are formed.

102. Testes

103. Oogenesis Oogenesis occurs in the ovaries of females and results in the formation of egg cells. For each cell that starts oogenesis, one healthy egg cell is formed and 3 polar bodies are also produced. Polar bodies are egg cells with no or very little cytoplasm.

104. Ovary

105. During cytokinesis I and cytokinesis II of meiosis, the cytoplasm is unequally divided between the egg cells. This results in one functioning egg cell and three nonfunctioning polar bodies. The polar bodies eventually degenerate.

106. The reason that egg cells form this way is that egg cells have to spend several days after they have been fertilized without being attached to the food source of the Mother. This increased egg size allows enough nutrients to be stored in the egg to survive until the placenta begins to function.

107. Sexual Reproduction Sexual reproduction is the production of offspring through meiosis and then the union of sperm and egg. Offspring produced by sexual reproduction are genetically different from their parents. Identical twins carry identical DNA. New combinations of genes are beneficial.

108. Name the pictured phases.