Outline – Cell Reproduction
Reproduction - Like begets like, more or less
ƒLiving organisms reproduce by two methods
1. Overview of Cell Reproduction
2. Cell Reproduction in Prokaryotes
3. Cell Reproduction in Eukaryotes
1. Chromosomes
2. Cell Cycle
3. Mitosis and Cytokinesis
4. Sexual Life Cycle & Meiosis
–Asexual reproduction
–Offspring are identical to the original cell or organism
–Involves inheritance of all genes from one parent
–Sexual reproduction
–Offspring are similar to parents, but show variations in traits
–Involves inheritance of unique sets of genes from two parents
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Roles of Cell Division
Examples of Cell Numbers
–Asexual reproduction
–
–
–
–
Reproduction of an entire single-celled organism
Growth of a multicellular organism
Growth from a fertilized egg into an adult
Repair and replacement of cells in an adult
Human Body Æ 50,000,000,000,000 cells
Red blood cells Æ 25,000,000,000
RBCs replaced every day Æ 1,400,000,000
–Sexual reproduction
– Sperm and egg production
Intestinal Epithelium Cells Æ Last 1.5 days
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Figure 8.3A
Binary fission of a prokaryotic cell
Genome Size Varies
Plasma
membrane
Prokaryotic
chromosome
Cell wall
1
Duplication of chromosome
and separation of copies
2
Cell elongation and
movement of DNA copies
Protein Ring
3 Division into
two daughter cells
Prokaryotic
Chromosomes
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Eukaryote Chromosome Structure
Chromosome Structure
Chromatids
Chromosome
Chromosome
Centromere
Replication
Chromatids
DNA
Histone
Protein
Centromere
2
Chromosome
Duplication &
Distribution
Centromere
Karyotype of Human Chromosomes
Chromosome
duplication
Sister
chromatids
Chromosome
distribution
to
daughter
cells
Chromosome Numbers
The cell cycle multiplies cells
ƒ The cell cycle is an ordered sequence of events for cell
division
ƒ It consists of two stages
– Interphase: duplication of cell contents
– G1—growth, increase in cytoplasm
– S—duplication of chromosomes
– G2—growth, preparation for division
– Mitotic phase: division
– Mitosis—division of the nucleus
– Cytokinesis—division of cytoplasm
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Cell Cycle of Eukaryotes
INTERPHASE
G1
S - DNA Synthesis
is
ito
si
s
s
ne
G2
G2 – Mitochondria
replicate
Chromosomes
condense
M
C
i
ok
yt
INTERPHASE
G1 - Primary Growth
S
Mitotic Phase
Mitosis in Eukaryotes
Mitosis – Separation of Chromosomes
“Division” of Nucleus
Stages of Mitosis
Prophase
Metaphase
Anaphase
M – Chromosomes condense and
chromatids separate
Telophase
C –Cytoplasm separates
Cytokinesis
The stages of cell division
The stages of cell division (part 2)
LM
250×
Figure 8.6
INTERPHASE
Centrosomes
Chromatin
PROPHASE
PROMETAPHASE
Centrosome Nuclear
Mitotic
Envelope
Fragments
spindle
METAPHASE
ANAPHASE
TELOPHASE
Kinetochore
Spindle
Nucleus
Plasma
membrane
Chromatids
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Centromere
Spindle
Microtubules
Metaphase
plate
Chromatids
Separating
Nuclear envelope
forming
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Figure 8.7A
Cytokinesis in an animal cell
Cell plate formation
in a plant cell
Wall of
Cell plate Daughter
parent cell forming nucleus
SEM 140×
Cleavage
furrow
Cleavage furrow
New cell wall
Cell wall
Contracting ring of
microfilaments
Daughter cells
Vesicles containing Cell plate Daughter cells
cell wall material
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Mitosis in Plant Cells
INTERPHASE (cell growth and chromosome duplication)
S
(DNA synthesis)
G1
Cytokinesis
Mitosis
(division of
(division
cytoplasm)
of nucleus)
G2
Genetically
Identical
“daughter
cells”
MITOTIC PHASE (M)
5
Controlling the Cell Cycle
Applying Knowledge about Cell Division
Human cells have 46 chromosomes.
By the end of interphase
G1 checkpoint
G0
–How many chromosomes are present in one cell?
Control
system
G1
–How many chromatids are present in one cell?
M
M checkpoint
S
G2
G2 checkpoint
Figure 8.9A
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Controlling the Cell Cycle
Controlling the Cell Cycle
Growth factor
Plasma membrane
Receptor
protein
Relay
proteins
Signal
transduction
pathway
Cyclins & CyclinDependent
Kinases
G1 checkpoint
Control
system
G1
M
S
G2
Figure 8.9B
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Tumors
Cancer cells produce tumors
Lymph
vessels
ƒCancer cells escape controls on the cell cycle
Tumor
Blood
vessel
– Cancer cells divide rapidly
– They spread to other tissues through the circulatory system
– Growth is not inhibited by other cells, and tumors form
– Benign tumors remain at the original site
– Malignant tumors spread to other locations by metastasis
Single
cancer
cell.
Invade
Neighboring
Tissue
Metastasize
Cancer cells escape controls on the cell cycle
Cancer cells divide rapidly
Growth is not inhibited Æ tumors form
Benign tumors remain at the original site
Malignant tumors spread to other locations by
metastasis
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Interfering with Cell Division
END
ENDMitosis
Mitosis
Radiation
Chemotherapy
Periwinkle - Vinblastin
Pacific Yew - Taxol
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Meiosis – Learning Goals
1. Understand the differences between homologous
chromosomes and sister chromatids.
2. Distinguish between
1. autosomes and sex chromosomes.
2. somatic cells and reproductive cells
3. diploid cells and haploid cells.
3. Describe and recognize the events of meiosis
4. Describe similarities & differences between mitosis and
meiosis.
5. Explain how meiosis contributes to genetic variation in
sexually reproducing organisms.
Meiosis
Sexual Life Cycle
8.13 Gametes have a single set of chromosomes
Haploid gametes (n = 23)
n
ƒ Meiosis is a process that converts diploid cells to haploid
cells
Egg cell
–Diploid cells have two sets of homologous chromosomes
n
–Haploid cells have one set of chromosomes
Sperm cell
Meiosis
Fertilization
Diploid
zygote
(2n = 46)
Multicellular
diploid adults
(2n = 46)
2n
–Meiosis occurs in the sex organs, producing gametes —
sperm and eggs
ƒ Fertilization is the union of sperm and egg
–The zygote has a diploid chromosome number, one set
from each parent
Mitosis and development
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Preparation of a karyotype from a blood sample
Hypotonic
solution
Blood
culture
White
blood
cells
Centrifuge
2
1
Fixative
Diploid Organisms have Pairs of
Homologous Chromosomes
Homologous Chromosomes
Stain
3
Centromere
2,600×
Homologous
chromosomes
Sister chromatids
5
4
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Homologous chromosomes have similar genetic
information
Coat-color
genes
Eye-color
genes
Brown
Black
C
E
Stages of Meiosis
Meiosis I
Meiosis II
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II
Homologous
Pair
c
White
e
Pink
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Meiosis I - Prophase
Meiosis I: Prophase: Synapsis and Crossover
Synapsis
1. Chromosomes condense
2. Nuclear envelope dissolves
Crossover
3. Centrioles move apart
4. Spindle apparatus forms
5. Synapsis - Homologous
chromosomes pair up
Homologous Chromosomes
after crossover
Animation
Meiosis I - Metaphase
1. Homologous chromosomes
align in an equatorial plane
Meiosis I - Anaphase
1. Homologous chromosomes
separate
2. Reduction division of
chromosomes where
2N Æ 1N
10
Figure 8.14 The stages of meiosis
Meiosis I - Telophase
1. Chromosomes decondense
2. Nuclear membrane forms
MEIOSIS I: Homologous chromosomes separate
INTERPHASE
3. Spindle apparatus disappears
Centrosomes
PROPHASE I
METAPHASE I
ANAPHASE I
Sister chromatids
Crossing over
Spindle
4. Cytokinesis – Two haploid
daughter cells form
Haploid Daughter Cells
Chromatin
Sister
chromatids
Homologous
chromosomes
pair up
Homologous
chromosomes
separate
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Figure 8.14 The stages of meiosis
Meiosis - Summary
MEIOSIS II: Chromatids separate
TELOPHASE I
AND CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
AND CYTOKINESIS
Sister chromatids separate
Haploid daughter
cells form
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Figure 8.15 Comparison of mitosis and meiosis
MITOSIS
Nondisjunction in meiosis I
MEIOSIS
Parent cell
(before chromosome replication)
MEIOSIS I
Prophase I
Prophase
Tetrad formed
by synapsis of
homologous
chromosomes
Chromosome
replication
Chromosome
replication
Duplicated
chromosome
(two sister chromatids)
2n = 4
Metaphase
Chromosomes
align at the
metaphase plate
Tetrads
align at the
metaphase plate
Anaphase
Telophase
Sister chromatids
separate during
anaphase
Homologous
chromosomes
separate during
anaphase I;
sister
chromatids
remain together
2n
Daughter cells
of mitosis
2n
No further
chromosomal
replication; sister
chromatids
separate
during
anaphase II
Metaphase I
Normal
meiosis II
Anaphase I
Telophase I
Haploid
n=2
Daughter
cells of
meiosis I
Gametes
MEIOSIS II
n
n
n
n
Daughter cells of meiosis II
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n+1
n+1 n−1 n−1
Number of chromosomes
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Fertilization after Nondisjunction
Nondisjunction - Down syndrome = Trisomy 21
1. Most common birth defect
2. 1 in 700
3. Physical features
Round face
Flattened nose bridge
Short stature
Heart defects
4. Susceptibility to infections
Egg cell
n+1
n (normal)
Nondisjunction
in meiosis I
Zygote
2n + 1
Sperm cell
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Figure 8.20C Maternal age and incidence of Down
syndrome
Sex Chromosome Disorders: Klinefelter syndrome (XXY)
Poor beard
growth
Gamete from
Male Parent
Infants with Down syndrome
(per 1,000 births)
90
Breast
Development
80
Gamete from
Female Parent
XY
X
70
60
Under-developed
testes
50
XXY
40
30
20
10
0
20
25
30
35
40
50
45
Age of mother
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Sex Chromosome Disorders: Turner syndrome (XO)
Web of
skin
Constriction
of aorta
Poor breast
development
Underdeveloped
ovaries
Gamete from
Male Parent
O
Gamete from
Female Parent
X
XO
Independent Assortment of chromosomes at metaphase I
Possibility 1 Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Short stature
99% die before birth
Normal Intelligence
Gametes
Combination 1 Combination 2
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Possibility 2
Combination 3 Combination 4
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Comparing Mitosis and Meiosis
END
Meiosis
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