1. Unit 5
Cell Reproduction

2. Eukaryotes Plants & animals
Prokaryotes and Eukaryotes reproduce differently!
Prokaryotes Bacteria
Eukaryotes Plants & animals
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3. Prokaryotes (Bacteria)
Lack a nucleus
Have a single circular chromosome
Reproduce asexually by
binary fission
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4. Steps in Binary Fission (2) (split)
Cells increase their cell mass slightly
DNA & cell components are replicated
Each cell divides into 2 daughter cells
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5. Binary Fission of Bacterial Cell
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6. E. Coli Dividing by Binary Fission
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7. Why do cells need to divide?
Eukaryotes
Contain a nucleus & membrane bound organelles
Eukaryotic Cells Reproduce Asexually through cell division
Why do cells need to divide?
To provide new cells for growth and repair.
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8. Cell Cycle of Eukaryotes
During the cell cycle:
a cell grows and prepares for division
divides it’s nucleus into 2
Divides the cytoplasm to form two daughter cells, each of which begins the cycle again

9. 3 main phases of the cell cycle

10. Cell Cycle has 3 major stages
1st stage: INTERPHASE: cell growth and
DNA replicated (copied)
2nd stage: MITOSIS: division of the
nucleus
3rd Stage: CYTOKINESIS: division
of the cell cytoplasm

11. CELL CYCLE

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Cell Cycle
Stages in growth & division
G1 Phase Interphase 90% of time
S phase “
G2 Phase “
M Phase Mitosis
Cytokinesis Cytokinesis
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Interphase: G1 Phase
First growth stage
Cell increases in size
Cell prepares to copy its DNA
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14. Interphase: Synthesis (S) Phase
Chromatin is copied. Now have 2 sets of DNA.
Synthesizing a copy of the DNA
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Interphase: G2 Phase
Cell duplicates organelles
Needed proteins and lipids are produced
“stock piling so each new cell will have what it needs”
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Check Points!
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MITOSIS : M Phase
Cell growth & protein production stop
4 stages of nuclear division happen in the following sequence:
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18. Mitosis
4 stages of Mitosis
Prophase
Metaphase
Anaphase
Telophase
PMAT

19. Steps in Prophase (before)
Chromatin coils tightly & becomes visible as chromosomes
Nuclear membrane disappears
Nuceolus disappears
Centrioles migrate to poles
Spindle fibers begins to form

20. Steps in Metaphase (Middle)
Spindle fibers from centrioles attach to each chromosome
Cell preparing to separate its chromosomes
(sister Chromatids)
Cell aligns its
chromosomes in the
middle of the cell

21. Steps in Anaphase
Cell chromosomes are separated (Sister Chromatids pulled apart)
Spindle fibers shorten so chromosomes are pulled to ends of cell

22. Anaphase

23. Steps in Telophase (two)
Separation of chromosomes (sister chromatids)completed
Cell Plate forms (plants)
Cleavage furrow forms(animals)
Nucleus & nucleolus reform
Two new nuclei form with new nuclear membrane.
Chromosomes uncoil and appear as chromatin
Mitosis ends

24. Telophase

25. Metaphase Interphase Prophase Anaphase Telophase
WARM-UP 3/6/07
What Stages of Mitosis can you find?

26. Cytokinesis: (not part of Mitosis)
Cytoplasm is completely divided into 2 complete and individual cells…smaller(1/2 the size) than the original.
Forms 2 Identical daughter cells.
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Mitosis/Cytokinesis results in the production of two genetically identical diploid cells. All cells undergo the cell cycle EXCEPT for sperm and Egg cells!!!
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28. Mitosis and Cytokinesis
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29. A closer look at chromosomes
DNA needs to duplicate and then separate to provide each daughter cell with an exact copy.
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30. Chromosome Condensed form of chromatin
a threadlike structure of nucleic acids and protein
Always paired with an identical copy of itself

31. Figure : Different levels of DNA condensation.
1. Double stranded DNA.
2. Chromatin strand (DNA with histones).
3. Condensed chromatin during interphase with centromere.
4. Condensed chromatin during interphase. (S Phase)
(Two copies of the DNA molecule are now present)
5. Super coiled Chromosome during prophase.

32. CHROMATID
Chromosome
SISTER CHROMATIDS

33. Chromosome

34. Types of Chromosomes Y X Autosomes
The 1st 22 pairs of Chromosomes in humans.
Sex Chromosomes
23rd pair
In females, the sex chromosomes are the 2 X chromosomes.
Males have one X chromosome and one Y chromosome.
The Y chromosome is what makes a baby boy. X Y

35. Is this a girl or a boy?

36. Part 2 Meiosis

37. What about egg cells?
A human Female is born with about 7 million immature egg cells.
Egg cells are generated through a process called oogenesis.
Each egg cell has only 1 copy of each chromosome and is called haploid with 23 chromosomes.
This reproductive cell is called a gamete

38. What about Sperm cells?
Sperm cells are made in the male testes through a process called spermatogenesis.
Sperm cells are derived from stem cells starting at the age of puberty.
Sperm cells have only 1 copy of every chromosome (23) haploid.
This haploid reproductive cell is called a gamete.

39. How are these cells produced with only 1 copy of each chromosome?
The process is called: MEIOSIS

40. Meiosis is very similar to Mitosis without
The Difference?
Meiosis is very similar to Mitosis without
Interphase in between
Lets see!

41. 1 cell becomes 4 cells called gametes
Meiosis
1 cell becomes 4 cells called gametes
Male gametes = Sperm
Female gametes = Eggs
Gamete + Gamete = Zygote

42. Why is it important to start with haploid cells? (1n)
Fertilization is the Union of
sperm (1n) and egg (1n)
Zygote is formed (2n)
The chromosome number is reduced in sperm and egg cells so at fertilization there is the correct # of chromosomes.

43. The process of meiosis Cuts chromosome # in half
Creates variation for Evolution
Makes offspring unique

44. This process is called MEIOSIS
Each organism must inherit a single copy of every chromosome from each of its “parents.”
Gametes(sperm and egg) are formed by a process that separates the two sets of chromosomes so that each gamete ends up with just one set.
This process is called MEIOSIS
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46. Chromosome Number All organisms have different numbers of chromosomes.
A body cell in an adult fruit fly has 8 chromosomes: 4 from the fruit fly's male parent, and 4 from its female parent.
These chromosomes are from a fruit fly. Each of the fruit fly’s body cells has 8 chromosomes.
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47. These two sets of chromosomes are said to be homologous.
Chromosome Number
These two sets of chromosomes are said to be homologous.
Each of the 4 chromosomes that came from the male fruit fly parent has a corresponding chromosome from the female fruit fly parent.
This is the same for humans. You have chromosomes 1-23 you got from your mother and you have chromosomes 1-23 from your father.
So you have 2 #1 chromosomes, 2 #2 chromosomes
2 #3 chromosomes…etc.
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48. Humans have 23 pairs of chromosomes, or a total of 46 chromosomes per cell (2N= 46). Each chromosome from a pair of Homologous Chromosomes comes from a different parent: one from the mother through the egg and the other from the father through the sperm. Homologous chromosomes carry alleles for the same genes.
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49. The gametes (egg or sperm) are haploid with one chromosome from each homologous pair. The total number of chromosomes in each gamete cell is 23 (N= 23).
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50. A Homologous Chromosome Pair:-
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51. Human haploid = 1n=23 = gamete (sperm/egg)
Chromosome Number
A cell that contains both sets of homologous chromosomes is said to be diploid.
The number of chromosomes in a diploid cell is sometimes represented by the symbol 2N.
Human haploid = 1n=23 = gamete (sperm/egg)
Human Diploid = 2n= sperm + egg
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52. What happens during the process of meiosis?
Phases of Meiosis
What happens during the process of meiosis?
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53. Meiosis is a process of reduction division in which
Phases of Meiosis
Phases of Meiosis
Meiosis is a process of reduction division in which
the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.
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54. Meiosis involves two divisions, meiosis I and meiosis II.
Phases of Meiosis
Meiosis involves two divisions, meiosis I and meiosis II.
By the end of meiosis II, the diploid cell that entered meiosis has become 4 haploid cells.
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55. Meiosis I Meiosis I Interphase I Prophase I Metaphase I Anaphase I
Phases of Meiosis
Meiosis I
Meiosis I
Interphase I
Prophase I
Metaphase I
During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell.
Anaphase I
Telophase I and Cytokinesis
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56. Phases of Meiosis
Cells undergo a round of DNA replication, forming duplicate chromosomes.
Interphase I
Interphase I - Cells undergo a round of DNA replication, forming duplicate chromosomes.
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57. There are 4 chromatids in a tetrad.
Phases of Meiosis
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
There are 4 chromatids in a tetrad.
Chromosome 1 lines up with chromosome 1
Chromosome 2 lines up with chromosome 2…on and on
MEIOSIS I
Prophase I
MEIOSIS I Prophase I - Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
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58. Crossing-over produces new combinations of alleles.
Phases of Meiosis
When homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over.
(also called Synapsis)
Crossing-over produces new combinations of alleles.
Crossing-over occurs during meiosis. (1) Homologous chromosomes form a tetrad. (2) Chromatids cross over one another. (3) The crossed sections of the chromatids are exchanged.
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59. Spindle fibers attach to the chromosomes.
Phases of Meiosis
Spindle fibers attach to the chromosomes.
MEIOSIS I
Metaphase I
MEIOSIS I Metaphase I - Spindle fibers attach to the chromosomes.
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60. Phases of Meiosis
MEIOSIS I
Anaphase I
The fibers seperate the homologous chromosomes toward opposite ends of the cell.
MEIOSIS I Anaphase I - The fibers pull the homologous chromosomes toward opposite ends of the cell.
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61. Nuclear membranes form. The cell separates into two cells.
Phases of Meiosis
MEIOSIS I
Telophase I and
Cytokinesis
Nuclear membranes form.
The cell separates into two cells.
The two cells produced by meiosis I have chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I.
MEIOSIS I Telophase I and Cytokinesis - Nuclear membranes form. The cell separates into two cells.
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62. Unlike meiosis I, neither cell goes through chromosome replication.
Phases of Meiosis
Meiosis II
The two cells produced by meiosis I now enter a second meiotic division.
Unlike meiosis I, neither cell goes through chromosome replication.
Each of the cell’s chromosomes has 2 chromatids.
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63. Meiosis II Phases of Meiosis Meiosis II Telophase I and Cytokinesis I
During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell.
Meiosis II
Telophase I and Cytokinesis I
Metaphase II
Anaphase II
Telophase II and Cytokinesis
Prophase II
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64. Phases of Meiosis
MEIOSIS II
Prophase II
Centrioloes move to opposite sides of the cell and start spindle fibers
MEIOSIS II Prophase II - Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell.
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65. The chromosomes line up in the center of cell.
Phases of Meiosis
MEIOSIS II
Metaphase II
The chromosomes line up in the center of cell.
MEIOSIS II Metaphase II - The chromosomes line up in a similar way to the metaphase state of mitosis.
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66. Phases of Meiosis
MEIOSIS II
Anaphase II
The sister chromatids separate and move toward opposite ends of the cell.
MEIOSIS II Anaphase II - The sister chromatids separate and move toward opposite ends of the cell.
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67. Meiosis II results in four haploid (N) daughter cells.
Phases of Meiosis
MEIOSIS II
Telophase II and Cytokinesis
Meiosis II results in four haploid (N) daughter cells.
MEIOSIS II Telophase II and Cytokinesis - Meiosis II results in four haploid (N) daughter cells.
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68. Gamete Formation
Gamete Formation
In male animals, meiosis results in four equal-sized gametes called sperm.
Meiosis produces four genetically different haploid cells. In males, meiosis results in four equal-sized gametes called sperm.
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69. Gamete Formation
In many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction.
Meiosis produces four genetically different haploid cells. In females, only one large egg cell results from meiosis. The other three cells, called polar bodies, usually are not involved in reproduction.
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70. The first division, meiosis I, separates homologous chromosomes.
Meiosis reduces chromosome number by copying the chromosomes once (during interphase of the cell cycle)
but dividing twice.
The first division, meiosis I, separates homologous chromosomes.
The second, meiosis II, separates sister chromatids.
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71. Sexual life cycles produce genetic variation 3 ways
1) Law of Segregation
chromosome pairs separate during meiosis
2) Law of independent assortment genes are separated randomly (shuffle)
3) Crossing Over
chromosome parts break off & reattach to other chromosomes creates new chromosome

72. Independent assortment of chromosomes contributes to genetic variability due to the random orientation of tetrads at the metaphase plate.
There is a fifty-fifty chance that a particular daughter cell of meiosis I will get the maternal chromosome of a certain homologous pair and a fifty-fifty chance that it will receive the paternal chromosome.

73. Comparing Mitosis and Meiosis
How is meiosis different from mitosis?
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75. Comparing Mitosis and Meiosis
Mitosis results in the production of two genetically identical diploid cells.
Meiosis produces four genetically different haploid cells.
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76. Comparing Mitosis and Meiosis
Cells produced by mitosis have the same number of chromosomes as the original cell.
These cells are genetically identical to the parent diploid cell and from each other.
Some organisms reproduce asexually by mitosis. Mitosis allows an organism to grow and replace cells.
Meiosis
Cells produced by meiosis have half the number of chromosomes as the parent cell.
These cells are genetically different from the diploid cell and from each other.
Meiosis is how sexually-reproducing organisms produce gametes.
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77. Copyright © 2002 Pearson Education, Inc
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

78. Chromosomes How do we look at the chromosomes of an individual?
The collection of chromosomes found in an individual’s cells
Karyotype

79. Chromosomes How is a Karyotype made?
Chemically treat and stain chromosomes in cells from a blood sample
The chromosomes are then photographed, cut out, arranged in pairs from largest to smallest, and numbered

80. Chromatin
Chromosome Scatter
Karyotype

81. This is a very complex process and as you can imagine, sometimes the events can have mistakes.

82. Chromosomes Abnormalities
Nondisjunction (NOT-COMING-APART)
Chromosomes fail to separate properly in
Anaphase II
Causes:
1. Monosomy (missing chromosome) most do not survive to be born
EX: Turner female (XO)
Trisomy (extra chromosome)
EX: Down syndrome

83. Chromatids do not Separate in Anaphase II
Nondisjunction
TRISOMY
MONOSOMY
NORMAL X x l
Chromatids do not Separate in Anaphase II

84. 2. Mutations: changes in Chromosome Structure
Deletion part of the chromosome breaks off
Duplication Part of the chromosome is repeated

85. Cancer
Mutations in genes that control normal cell division can lead to cancer.
Increasing your risk
Sun without sun block
Smoking or being around 2nd hand smoke
Working with known cancer causing chemicals.

86. Proto-Oncogenes are normal genes that code proteins involved in a cell's normal growth
Oncogenes instruct cells to make proteins that stimulate excessive cell growth and division.
*Oncogenes are Mutant Forms(bad) of Proto-Oncogenes*

87. Tumor Suppressor Genes
Normal genes whose ABSENCE can lead to cancer.
Genes come in pairs, one from each parent
A defect in one copy will not cause cancer because the other normal copy is still functional.

88. Uncontrolled Cell Growth
Cancer cells divide uncontrollably and form masses of cells called tumors that can damage the surrounding tissues.
Cancer cells may break loose from tumors and spread throughout the body, disrupting normal activities and causing serious medical problems or even death.
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