Chapter 6
Chromosomes and Cell Reproduction
Table of Contents
Section 1 Chromosomes
Section 2 The Cell Cycle
Section 3 Mitosis and Cytokinesis
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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.
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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.
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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.
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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.
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Chapter 6
Section 1 Chromosomes
Binary Fission
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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.
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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.
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Chapter 6
Section 1 Chromosomes
Chromosome Structure
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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.
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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.
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Chapter 6
Section 1 Chromosomes
Comparing Haploid and Diploid Cells
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Chapter 6
Section 1 Chromosomes
Chromosome
Number of
Various
Organisms
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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.
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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.
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Chapter 6
Section 1 Chromosomes
Sex Chromosomes and Autosomes
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Chapter 6
Section 1 Chromosomes
Karyotype
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Chapter 6
Section 1 Chromosomes
Chromosome Number
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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
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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.
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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.
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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.
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Chapter 6
Section 2 The Cell Cycle
Cell Cycle G1 Phase
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Chapter 6
Section 2 The Cell Cycle
Cell Cycle S Phase
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Chapter 6
Section 2 The Cell Cycle
Cell Cycle G2 Phase
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Chapter 6
Section 2 The Cell Cycle
Cell Cycle M Phase
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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).
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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.
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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.
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Uncontrolled cell division: Cancer
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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.
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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.
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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.
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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.
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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
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Chapter 6
Section 3 Mitosis and Cytokinesis
Stages of Mitosis
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Chapter 6
Section 3 Mitosis and Cytokinesis
Mitosis
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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.
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Chapter 6
Section 3 Mitosis and Cytokinesis
Comparing Cell Division in Plants and Animals
–In animal cells, the
membrane
pinches closed.
–In plant cells, a cell
plate forms.
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Chapter 6
Standardized Test Prep
Multiple Choice
The illustration below shows the events of the cell cycle.
Use the figure below to answer questions 1–3.
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
1. For about what proportion of the cell cycle is the cell
in interphase?
A.
B.
C.
D.
less than 1/2
less than 3/4
more than 3/4
more than 9/10
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
1. For about what proportion of the cell cycle is the cell
in interphase?
A.
B.
C.
D.
less than 1/2
less than 3/4
more than 3/4
more than 9/10
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
2. List the phases of the cell cycle starting immediately
after cell division.
F.
G.
H.
J.
G1, S, G2, mitosis, cytokinesis
cytokinesis, G1, S, G2, mitosis
S, G2, mitosis, cytokinesis, G1
G1, cytokinesis, mitosis, G2, S
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Chapter 6
Standardized Test Prep
Multiple Choice, continued
2. List the phases of the cell cycle starting immediately
after cell division.
F.
G.
H.
J.
G1, S, G2, mitosis, cytokinesis
cytokinesis, G1, S, G2, mitosis
S, G2, mitosis, cytokinesis, G1
G1, cytokinesis, mitosis, G2, S
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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.
B.
C.
D.
Mitosis would immediately follow S.
Cytokinesis would immediately follow G2.
G1 would immediately follow mitosis.
G2 would immediately follow G1.
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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.
B.
C.
D.
Mitosis would immediately follow S.
Cytokinesis would immediately follow G2.
G1 would immediately follow mitosis.
G2 would immediately follow G1.
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