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2. Standardized Test Prep
Resources
Chapter Presentation
Visual Concepts
Transparencies
Standardized Test Prep

3. Chapter 6 Table of Contents Section 1 Chromosomes
Chromosomes and Cell Reproduction
Table of Contents
Section 1 Chromosomes
Section 2 The Cell Cycle
Section 3 Mitosis and Cytokinesis

4. Chapter 6
Section 1 Chromosomes
Objectives
Identify four examples of cell division in eukaryotes and one example in prokaryotes.
Differentiate between a gene, a DNA molecule, a chromosome, and a chromatid.
Differentiate between homologous chromosomes, autosomes, and sex chromosomes.
Compare haploid and diploid cells.
Predict how changes in chromosome number or structure can affect development.

5. Formation of New Cells by Cell Division
Chapter 6
Section 1 Chromosomes
Formation of New Cells by Cell Division
Cell division, also called cell reproduction, occurs in humans and other organisms at different times in their life.
The formation of gametes involves yet a special type of cell division. Gametes are an organism’s reproductive cells, such as sperm or egg cells.
When a cell divides, the DNA is first copied and then distributed.

6. Chapter 6 Gamete Section 1 Chromosomes
Click below to watch the Visual Concept.
Visual Concept

7. Formation of New Cells by Cell Division, continued
Chapter 6
Section 1 Chromosomes
Formation of New Cells by Cell Division, continued
Prokaryotic Cell Reproduction
Prokaryotes reproduce by a type of cell division called binary fission.
Binary fission is a form of asexual reproduction that produces identical offspring.
In asexual reproduction, a single parent passes exact copies of all of its DNA to its offspring.

8. Formation of New Cells by Cell Division, continued
Chapter 6
Section 1 Chromosomes
Formation of New Cells by Cell Division, continued
Prokaryotic Cell Reproduction
Binary fission occurs in two stages: first, the DNA is copied (so that each new cell will have a copy of the genetic information), and then the cell divides.
Eventually the dividing prokaryote is pinched into two independent cells.

9. Chapter 6
Section 1 Chromosomes
Binary Fission

10. Formation of New Cells by Cell Division, continued
Chapter 6
Section 1 Chromosomes
Formation of New Cells by Cell Division, continued
Eukaryotic Cell Reproduction
A gene is a segment of DNA that codes for a protein or RNA molecule.
When genes are being used, the DNA is stretched out so that the information it contains can be used to direct the synthesis of proteins.
As a eukaryotic cell prepares to divide, the DNA and the proteins associated with the DNA coil into a structure called a chromosome.

11. Chapter 6 Gene Section 1 Chromosomes
Click below to watch the Visual Concept.
Visual Concept

12. Chapter 6
Section 1 Chromosomes
Chromosome

13. Homologous Chromosomes
Chapter 6
Section 1 Chromosomes
Homologous Chromosomes

14. Formation of New Cells by Cell Division, continued
Chapter 6
Section 1 Chromosomes
Formation of New Cells by Cell Division, continued
Eukaryotic Cell Reproduction
The two exact copies of DNA that make up each chromosome are called chromatids.
The two chromatids of a chromosome are attached at a point called a centromere.
The chromatids, which become separated during cell division and placed into each new cell, ensure that each new cell will have the same genetic information as the original cell.

15. Chapter 6
Section 1 Chromosomes
Chromosome Structure

16. Chapter 6 Parts of a Chromosome Section 1 Chromosomes
Click below to watch the Visual Concept.
Visual Concept

17. Comparing Cell Division in Prokaryotes and Eukaryotes
Chapter 6
Section 1 Chromosomes
Comparing Cell Division in Prokaryotes and Eukaryotes

18. How Chromosome Number and Structure Affect Development
Chapter 6
Section 1 Chromosomes
How Chromosome Number and Structure Affect Development
Sets of Chromosomes
Homologous chromosomes are chromosomes that are similar in size, shape, and genetic content.
Each homologue in a pair of homologous chromosomes comes from one of the two parents.
The 46 chromosomes in human somatic cells are actually two sets of 23 chromosomes.

19. How Chromosome Number and Structure Affect Development, continued
Chapter 6
Section 1 Chromosomes
How Chromosome Number and Structure Affect Development, continued
Sets of Chromosomes
When a cell, such as a somatic cell, contains two sets of chromosomes, it is said to be diploid.
When a cell, such as a gamete, contains one set of chromosomes, it is said to be haploid.
The fusion of two haploid gametes—a process called fertilization—forms a diploid zygote. A zygote is a fertilized egg cell.

20. Comparing Haploid and Diploid Cells
Chapter 6
Section 1 Chromosomes
Comparing Haploid and Diploid Cells

21. Chromosome Number of Various Organisms
Chapter 6
Section 1 Chromosomes
Chromosome Number of Various Organisms

22. How Chromosome Number and Structure Affect Development, continued
Chapter 6
Section 1 Chromosomes
How Chromosome Number and Structure Affect Development, continued
Sex Chromosomes
Autosomes are chromosomes that are not directly involved in determining the sex (gender) of an individual.
The sex chromosomes, one of the 23 pairs of chromosomes in humans, contain genes that will determine the sex of the individual.
In humans and many other organisms, the two sex chromosomes are referred to as the X and Y chromosomes.

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

24. The Role of Sex Chromosomes in Sex Determination
Chapter 6
Section 1 Chromosomes
The Role of Sex Chromosomes in Sex Determination
Click below to watch the Visual Concept.
Visual Concept

25. How Chromosome Number and Structure Affect Development, continued
Chapter 6
Section 1 Chromosomes
How Chromosome Number and Structure Affect Development, continued
Change in Chromosome Number
Humans who are missing even one of the 46 chromosomes do not survive.
Humans with more than two copies of a chromosome, a condition called trisomy, will not develop properly.
Abnormalities in chromosome number can be detected by analyzing a karyotype, a photo of the chromosomes in a dividing cell that shows the chromosomes arranged by size.

26. Chapter 6
Section 1 Chromosomes
Karyotype

27. Chapter 6
Section 1 Chromosomes
Chromosome Number

28. Chapter 6 Karyotype Section 1 Chromosomes
Click below to watch the Visual Concept.
Visual Concept

29. How Chromosome Number and Structure Affect Development, continued
Chapter 6
Section 1 Chromosomes
How Chromosome Number and Structure Affect Development, continued
Change in Chromosome Structure
Changes in an organism’s chromosome structure are called mutations.
Breakage of a chromosome can lead to four types of mutations:
1. deletion mutation
2. duplication mutation
3. inversion mutation
4. translocation mutation

30. Types of Chromosome Mutations
Chapter 6
Section 1 Chromosomes
Types of Chromosome Mutations
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Visual Concept

31. Chapter 6
Section 2 The Cell Cycle
Objectives
Identify the major events that characterize each of the five phases of the cell cycle.
Describe how the cell cycle is controlled in eukaryotic cells.
Relate the role of the cell cycle to the onset of cancer.

32. The Life of a Eukaryotic Cell
Chapter 6
Section 2 The Cell Cycle
The Life of a Eukaryotic Cell
The Cell Cycle
The cell cycle is a repeating sequence of cellular growth and division during the life of an organism.
A cell spends 90 percent of its time in the first three phases of the cycle, which are collectively called interphase.

33. Cell Cycle Introduction
Chapter 6
Section 2 The Cell Cycle
Cell Cycle Introduction

34. The Life of a Eukaryotic Cell, continued
Chapter 6
Section 2 The Cell Cycle
The Life of a Eukaryotic Cell, continued
The Cell Cycle
The five phases of the cell cycle are:
1. First growth (G1) phase During the G1 phase, a cell grows rapidly and carries out its routine functions.
2. Synthesis (S) phase A cell’s DNA is copied during this phase.
3. Second growth (G2) phase In the G2 phase, preparations are made for the nucleus to divide.
4. Mitosis The process during cell division in which the nucleus of a cell is divided into two nuclei is called mitosis.
5. Cytokinesis The process during cell division in which the cytoplasm divides is called cytokinesis.

35. Chapter 6
Section 2 The Cell Cycle
Cell Cycle G1 Phase

36. Chapter 6
Section 2 The Cell Cycle
Cell Cycle S Phase

37. Chapter 6
Section 2 The Cell Cycle
Cell Cycle G2 Phase

38. Chapter 6
Section 2 The Cell Cycle
Cell Cycle M Phase

39. Control of the Cell Cycle
Chapter 6
Section 2 The Cell Cycle
Control of the Cell Cycle
The cell cycle has key checkpoints (inspection points) at which feedback signals from the cell can trigger the next phase of the cell cycle (green light).
Other feedback signals can delay the next phase to allow for completion of the current phase (yellow or red light).

40. Control of the Cell Cycle, continued
Chapter 6
Section 2 The Cell Cycle
Control of the Cell Cycle, continued
Control occurs at three principal checkpoints:
1. Cell growth (G1) checkpoint This checkpoint makes the decision of whether the cell will divide.
2. DNA synthesis (G2) checkpoint DNA replication is checked at this point by DNA repair enzymes.
3. Mitosis checkpoint This checkpoint triggers the exit from mitosis.

41. Control of the Cell Cycle
Chapter 6
Section 2 The Cell Cycle
Control of the Cell Cycle
Click below to watch the Visual Concept.
Visual Concept

42. Control of the Cell Cycle, continued
Chapter 6
Section 2 The Cell Cycle
Control of the Cell Cycle, continued
When Control Is Lost: Cancer
Certain genes contain the information necessary to make the proteins that regulate cell growth and division.
If one of these genes is mutated, the protein may not function, and regulation of cell growth and division can be disrupted.
Cancer, the uncontrolled growth of cells, may result.

43. Chapter 6
Section 3 Mitosis and Cytokinesis
Objectives
Describe the structure and function of the spindle during mitosis.
Summarize the events of the four stages of mitosis.
Differentiate cytokinesis in animal and plant cells.

44. Chromatid Separation in Mitosis
Chapter 6
Section 3 Mitosis and Cytokinesis
Chromatid Separation in Mitosis
During mitosis, the chromatids on each chromosome are physically moved to opposite sides of the dividing cell with the help of the spindle.
Spindles are cell structures made up of both centrioles and individual microtubule fibers that are involved in moving chromosomes during cell division.

45. Chromatid Separation in Mitosis, continued
Chapter 6
Section 3 Mitosis and Cytokinesis
Chromatid Separation in Mitosis, continued
Forming the Spindle
When a cell enters the mitotic phase, the centriole pairs start to separate, moving toward opposite poles of the cell.
As the centrioles move apart, the spindle begins to form.

46. Chromatid Separation in Mitosis, continued
Chapter 6
Section 3 Mitosis and Cytokinesis
Chromatid Separation in Mitosis, continued
Separation of Chromatids by Attaching Spindle Fibers
The chromatids are moved to each pole of the cell in a manner similar to bringing in a fish with a fishing rod and reel.
When the microtubule “fishing line” is “reeled in,” the chromatids are dragged to opposite poles.
As soon as the chromatids separate from each other they are called chromosomes.

47. Mitosis and Cytokinesis
Chapter 6
Section 3 Mitosis and Cytokinesis
Mitosis and Cytokinesis
Mitosis
Step 1 Prophase The nuclear envelope dissolves and a spindle forms.
Step 2 Metaphase During metaphase the chromosomes move to the center of the cell and line up along the equator.
Step 3 Anaphase Centromeres divide during anaphase.
Step 4 Telophase A nuclear envelope forms around the chromosomes at each pole. Mitosis is complete.

48. Chapter 6
Section 3 Mitosis and Cytokinesis
Stages of Mitosis

49. Snapshot of Mitotic Structures
Chapter 6
Section 3 Mitosis and Cytokinesis
Snapshot of Mitotic Structures
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Visual Concept

50. Chapter 6
Section 3 Mitosis and Cytokinesis
Mitosis

51. Mitosis and Cytokinesis, continued
Chapter 6
Section 3 Mitosis and Cytokinesis
Mitosis and Cytokinesis, continued
Cytokinesis
As mitosis ends, cytokinesis begins.
During cytokinesis, the cytoplasm of the cell is divided in half, and the cell membrane grows to enclose each cell, forming two separate cells as a result.
The end result of mitosis and cytokinesis is two genetically identical cells where only one cell existed before.

52. Comparing Cell Division in Plants and Animals
Chapter 6
Section 3 Mitosis and Cytokinesis
Comparing Cell Division in Plants and Animals
Click below to watch the Visual Concept.
Visual Concept

53. Chapter 6 Multiple Choice
Standardized Test Prep
Multiple Choice
The illustration below shows the events of the cell cycle. Use the figure below to answer questions 1–3.

54. Multiple Choice, continued
Chapter 6
Standardized Test Prep
Multiple Choice, continued
1. For about what proportion of the cell cycle is the cell in interphase?
A. less than 1/2
B. less than 3/4
C. more than 3/4
D. more than 9/10

55. Multiple Choice, continued
Chapter 6
Standardized Test Prep
Multiple Choice, continued
1. For about what proportion of the cell cycle is the cell in interphase?
A. less than 1/2
B. less than 3/4
C. more than 3/4
D. more than 9/10

56. Multiple Choice, continued
Chapter 6
Standardized Test Prep
Multiple Choice, continued
2. List the phases of the cell cycle starting immediately after cell division.
F. G1, S, G2, mitosis, cytokinesis
G. cytokinesis, G1, S, G2, mitosis
H. S, G2, mitosis, cytokinesis, G1
J. G1, cytokinesis, mitosis, G2, S

57. Multiple Choice, continued
Chapter 6
Standardized Test Prep
Multiple Choice, continued
2. List the phases of the cell cycle starting immediately after cell division.
F. G1, S, G2, mitosis, cytokinesis
G. cytokinesis, G1, S, G2, mitosis
H. S, G2, mitosis, cytokinesis, G1
J. G1, cytokinesis, mitosis, G2, S

58. Multiple Choice, continued
Chapter 6
Standardized Test Prep
Multiple Choice, continued
3. If the phase during which DNA is synthesized did not occur, what effect would it have on the cell cycle?
A. Mitosis would immediately follow S.
B. Cytokinesis would immediately follow G2.
C. G1 would immediately follow mitosis.
D. G2 would immediately follow G1.

59. Multiple Choice, continued
Chapter 6
Standardized Test Prep
Multiple Choice, continued
3. If the phase during which DNA is synthesized did not occur, what effect would it have on the cell cycle?
A. Mitosis would immediately follow S.
B. Cytokinesis would immediately follow G2.
C. G1 would immediately follow mitosis.
D. G2 would immediately follow G1.