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Chapter 6
Chromosomes and Cell Reproduction
Section 1: Chromosomes
Section 2: The Cell Cycle
Section 3: Mitosis and Cytokinesis
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.
6.1 chromosomes
I. New Cells formed by Division
•
Cells divide or reproduce
–
In humans, about 2 trillion/day
1. DNA is copied and then distributed to each
new cell
2. Different processes occur in prokaryotes vs.
eukaryotes.
Section6.1
•Function of Cell Division
• allows organisms to reproduce asexually
• grow
• replace worn-out or damaged tissue
• form gametes.
Prokaryotic Cell Reproduction
• Bacteria reproduce asexually by
binary fission, a process that
produces identical offspring.
– Stage 1: DNA copied
– Stage 2: Cell divides by adding new
membranes and eventually pinching off
into 2 new cells.
– The 2 new cells contain the same DNA
and are identical to each other
New
membrane
pinching
inward
DNA
Bacteria cell dividing
Eukaryotic Cell Reproduction
• Before eukaryotic cell
division, DNA coils
tightly around proteins
and forms chromosomes.
• At cell division, each
chromosome consists of
two chromatids
attached at the centromere.
Section 1
How Chromosome Number and
Structure Affect Development
Sets of Chromosomes
• Each organism has a characteristic number of
chromosomes.
Mosquito
6
Garden pea
14
Saccharomyces (yeast)
18
Corn
20
human
46
Dog
78
Adder’s tongue fern
1,2
62
Types of chromosomes
• 2 basic types:
– Sex chromosomes(2) and Autosomes(44)
A little chomosome vocabulary
• diploid= cells having 2 sets of chromosomes
• Haploid= cells having 1 set of chromosomes
• Homologous= autosomes are homologues, meaning
they are the same shape, size and carry the genes for
the same traits.
Sets of chromosomes
• Human somatic cells or autosomes
– are diploid (2 sets of chromosomes)
– totaling 46 homologous chromosomes
• 23 chromosomes from each parent
Sex Chromosomes
carry information that determines an organism’s gender.
Either X or Y
•Human gametes are haploid,
with 23 chromosomes.
• 1 copy of the parents DNA
2 sex cells converge and make a
diploid cell
Section 1
How Chromosome Number and Structure Affect Development
Change in Chromosome Number
•Karyotypes are used to examine an
individual’s chromosomes and
identify possible abnormalities in
chromosome number.
•can cause abnormal development
or be fatal.
How Chromosome Number and Structure Affect Development
• tests are used to make
karyotypes in unborn
children
• Amniocentesis
(amniotic fluid)
• chorionic villi
sampling(placenta)
• Triosomy:
• more than 2
copies of
chromosomes
• normal
• Down’s
syndrome
Change in Chromosome Structure
Mutations can cause abnormal development.
• Deletion: missing genes
• Piece breaks off
• Usually fatal
• Duplication: repeated genes
• Fragment attaches to homologous chromosome
• Carries 2 copies
• Inversion: genes out of order
• Attaches to same chromosome in reverse order
• Translocation: genes relocated in wrong
place
• Reattaches to nonhomologous chromosome
Section 6.2-6.3
The Cell Cycle
Objectives:
•Identify the major events that characterize each of
the five phases of the cell cycle.
•Identify the major events of mitosis and cytokenisis
•Describe how the cell cycle is controlled in
eukaryotic cells.
•Relate the role of the cell cycle to the onset of
cancer.
Section 6.2
The Cell Cycle
The Life of a Eukaryotic Cell
•The Cell Cycle has 3 main stages/phases
•interphase
•mitosis
•cytokinesis.
Section 2
Control of the Cell Cycle
•Cell Checkpoints
•The cell cycle is carefully controlled through three
main checkpoints.:
•cell growth (G1) checkpoint,
• DNA synthesis (G2) checkpoint,
• mitosis checkpoint.
•When Control is Lost: Cancer
•Failure of control of cellular growth and
division can result in cancer.
Interphase: G1 phase
A cell spends 90 % of its
time in interphase.
Interphase consists of 3
phases
– G1 phase or growth
phase
• Cells grow and mature
• Carries out normal
functions
G1 Check point: Cell Growth
•Decides if the cell will grow or not
•If OK, then cell goes into S phase and divides normally
•If NOT OK, then cell goes into
resting period( G0 pahse)
cells can reactivate when
conditions change
or stay here
permamnently
Interphase: S phase
DNA synthesis (replication)
occurs
Each chromosome consists of
2 chromatids attached by a
centromere
Interphase: G2 phase
Replicated DNA and cell
prepare for cell division.
Microtubules in the
centrioles form to move
DNA
G2 check point: DNA Synthesis
•DNA replication is checked for typo’s in sequence and repaired by
enzymes.
•If DNA sequence passes inspection then the proteins made trigger
mitosis
M Phase: Mitosis
A cell about to divide enters the mitosis or M
phase.
– Mitosis has 4 stages of division
prophase
metaphase
anaphase
telophase
Prophase
• Chromosomes become
visible
• Nuclear envelope
dissolves
• Spidles form
Metaphase
• Chromosomes line up
along equator of cell
• Spindle fibers link to
the chromatids of each
chromosome to
opposite poles
Anaphase
• Centromeres divide
• Chromatides (now
called chromosomes)
move toward opposite
poles
End of anaphase
2 cells at the end of
anaphase.
Chromosomes have
been pulled to the
opposite poles in
these plant cells
Telophase
• Nuclear envelope
forms at each pole
• Chromosomes uncoil
• Spindles disolve
• Cytokenisis begins if
cell passes check point
Mitosis check point
Triggers exit from mitosis
Cells go into cytokinesis and then into G1 phase of
cellular growth
Last step: Cytokenesis
• Cytoplasm of the
cell divided in half.
– Plant cell: cell
plate forms
– Animals: protein
threads pinch cell
in half
• The cell
membrane/wall
grows to enclose
each cell
• Forming 2 new
identical cells
Anaphase
End telophase/cytokenisis
Prophase
Metaphase