Unit 3: Genetics
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The Cell Cycle + DNA structure/function
Mitosis and Meiosis
Mendelian Genetics (aka - fun with Punnett squares)
DNA replication
Yesterday’s Exit Ticket
phases of cell cycle
MITOTIC
PHASE
Mitotic Phase
Interphase
G1
S
G2 phase
G2(2nd gap)
Mitosis + Cytok.
What happens:
What happens:
What happens:
What happens:
•Growth
•DNA
replication
•More growth
and organelle
replication
•Division of
nucleus
•Division of cell
Today’s Agenda
• Cell Cycle and Mitosis
• Regulation of the Cell Cycle
– Checkpoints
• Meiosis and Sexual Reproduction
Phases and Stages within the Cell Cycle
phases of cell cycle
INTERPHASE
G1 Phase (1st gap)
Prophase
MITOTIC PHASE
S Phase (synthesis)
Prometaphase
G2 phase (2nd gap)
Metaphase
stages of mitosis
Anaphase
Mitosis +
Cytokinesis
Telophase
cytokinesis
3. Mitotic Phase
Stages of mitosis
G2 of Interphase
centrosomes
Nuclear Plasma
envelope membrane
Fig. 12-6
Videos:
Cartoon
https://www.youtube.com/watch?v=L0k-enzoeOM
Real Thing
https://www.youtube.com/watch?v=DD3IQknCEdc
3. Mitotic Phase
Stages of mitosis
First stage of mitosis
• Prophase
1) Chromosomes condense  they become
supercoiled for efficient movement during
subsequent processes
2) Preparation of the mitotic spindle  an
apparatus that will help guide chromosomes
3. Mitotic Phase
Stages of mitosis
Prophase
G2 of Interphase
spindle forming
Nuclear Plasma
envelope membrane
Condensed chromosome, consisting
of two sister chromatids
Fig. 12-6
3. Mitotic Phase
Stages of mitosis
Second stage of mitosis
• Prometaphase
1) Nuclear membrane breaks down
2) Spindle attaches to centromeres
3. Mitotic Phase
Stages of mitosis
G2 of Interphase
Prophase
spindle forming
Nuclear Plasma
envelope membrane
Prometaphase
Centromere
Fragments
of nuclear
envelope
Condensed chromosome
Centrosome
Fig. 12-6
3. Mitotic Phase
Stages of mitosis
Third stage of mitosis
• Metaphase
Chromosomes line up in the middle of the cell
3. Mitotic Phase
Stages of mitosis
Metaphase
Metaphase
plate
Spindle
Fig. 12-6
3. Mitotic Phase
Stages of mitosis
Fourth Stage of Mitosis
• Anaphase
Sister chromatids separate, pulled by spindle
3. Mitotic Phase
Stages of mitosis
Metaphase
Anaphase
Metaphase
plate
Sister chromatids
Spindle
Fig. 12-6
3. Mitotic Phase
Stages of mitosis
Fifth Stage of Mitosis
• Telophase
1) Nuclear membranes reform
2) Cytokinesis can begin at the same time
3. Mitotic Phase
Stages of mitosis
Metaphase
Anaphase
Metaphase
plate
Cleavage
furrow
Sister chromatids
Spindle
Telophase and Cytokinesis
Nuclear
envelope
forming
Fig. 12-6
3. Mitotic Phase
Summary
100 µm
Cleavage furrow
Daughter cells
(a) Cleavage of an animal cell (SEM)
Fig. 12-9a
3. Mitotic Phase
Summary
Vesicles
forming
cell plate
Wall of
parent cell
Cell plate
1 µm
New cell wall
(b) Cell plate formation
in a plant cell (TEM)
Daughter cells
Fig. 12-9b
Videos:
Cartoon
https://www.youtube.com/watch?v=L0k-enzoeOM
Real Thing
https://www.youtube.com/watch?v=DD3IQknCEdc
What is happening in this picture?
a) DNA molecules are being
replicated
b) chromosomes are condensing
c) nuclear envelope is breaking
down
d) sister chromatids are being
pulled apart
e) cleavage of cell
1
2
What is the right order for these
pictures, from first to last?
A. 1  3  2  4
B. 1  2  4  3
C. 3  4  1  2
D. 3  2  1  4
E. 2  3  1  4
3
4
Outline
• Cell Cycle and Mitosis
• Regulation of the Cell Cycle
– Checkpoints
• Meiosis and Sexual Reproduction
1) The concept of checkpoints
Overview
1) The concept of checkpoints
• Move on to the next phase only
if conditions are right.
• Prevents sick or precancerous cells
from dividing and maintains proper
cell number.
inflightinsider.com
2. Interphase
Overview
G0
G1 = “Gap 1”
S
growth
synthesis
G2 = “Gap 2”
growth
Which of these steps, if gone awry, could lead to cancer?
Fig. 12-14
G1 checkpoint
Control
system
G1
M
M checkpoint
G2 checkpoint
G2
S
Checkpoint sensing mechanisms monitor:
– Progression of the current phase
• Have we done everything we need to before we move on?
– DNA integrity
• Are all the As, Ts, Cs and Gs in place?
– Cell density
• Do any neighbors need to be replaced?
– Cell anchorage
• Am I hooked to something (good) or roaming free (bad)?
Fig. 12-19
Anchorage
Cell Density
25 µm
25 µm
(a) Normal mammalian cells
(b) Cancer cells
Fig. 12-15
G0
G1 checkpoint
G1
(a) Cell receives a go-ahead
signal
G1
(b) Cell does not receive a
go-ahead signal
Chemotherapy and the cell cycle
Chemotherapeutic drugs work by stopping cancer cells
from dividing. Many were first isolated from plants.
info.biotech-calendar.com
3) Chemotherapy and the cell cycle
Many chemotherapeutic drugs were first isolated from
plants.
Vinca alkaloids from the Madagascar periwinkle bind
to spindle building blocks, preventing their assembly.
3) Chemotherapy and the cell cycle
Many chemotherapeutic drugs were first isolated from
plants.
Vinca alkaloids from the Madagascar periwinkle bind
to spindle building blocks, preventing their assembly.
Which process in the cell cycle is most directly
blocked by Vinca alkaloids?
a)Chromosome condensation
b)Degradation of nuclear membrane
c)Attachment of spindle to chromosomes
d)Separation of sister chromatids
e)Cytokinesis
3) Chemotherapy and the cell cycle
Many chemotherapeutic drugs were first isolated from
plants.
Vinca alkaloids from the Madagascar periwinkle bind
to spindle building blocks, preventing their assembly.
3) Chemotherapy and the cell cycle
Many chemotherapeutic drugs were first isolated from
plants.
Podophyllotoxin from American and Himalayan mayapples
(endangered!) prevents DNA replication
3) Chemotherapy and the cell cycle
Many chemotherapeutic drugs were first isolated from
plants.
Podophyllotoxin from American and Himalayan
mayapples (endangered!) prevents DNA replication
In which part of the cell cycle would a cell be
stalled by podophyllotoxin?
a)Mitosis
b)Cytokinesis
c)S phase
d)G2
e)G1
3) Chemotherapy and the cell cycle
Chemotherapy stops the cell cycle
The most affected tissues have the most cell division.
-hair, nails
-skin
-bone marrow
-gut
Weirdasiannews.com; drlindirect.com; daviddarling.info
5 minute break
Seagrant.umn.edu
Outline
• Cell Cycle and Mitosis
• Regulation of the Cell Cycle
– Checkpoints
• Meiosis and Sexual Reproduction
Meiosis and Sexual Life Cycles
Musingsofahousewife.com
Meiosis Outline
1.
2.
3.
4.
Inheritance
Sexual reproduction
A detailed look at meiosis
Where does variation come from?
1. Inheritance
Two basic forms of reproduction:
1.Asexual reproduction: Mitosis
2.Sexual reproduction: two individuals contribute
genetic material to offspring
Some animals reproduce by making copies of themselves:
http://www.youtube.com/watch?v=489CSop00sY&feature=related
1. Inheritance
Two basic forms of reproduction:
1.Asexual
2.Sexual reproduction: two individuals contribute
genetic material to offspring
Outline
1. Inheritance
2. Sexual reproduction
a) The genetic makeup of organisms that reproduce
sexually
b) Fertilization and meiosis alternate in sexual life
cycles
3. A detailed look at meiosis
4. Where does variation come from?
2. Sexual reproduction
a) The genetic makeup of sexually reproducing organisms
Human chromosomes
Fig. 13.3, p. 250
2. Sexual reproduction
a) The genetic makeup of sexually reproducing organisms
Homologous chromosomes carry genes for the same inherited
characters
Diploid: cells that contain 2 sets of chromosomes
(ex: all human cells OTHER than our gametes)
Haploid: cells that have only one of each kind of chromosome
(ex: our gametes)
Notation:
chromosome number in diploid state = “2n”
chromosome number in haploid state = “n”
2. Sexual reproduction
b) Fertilization and meiosis alternate
meiosis
makes
haploid
cells
(gametes
or spores)
fertilization
makes a diploid
zygote
Fig. 13.5, p. 251
Outline
1.
2.
3.
4.
Inheritance
Sexual reproduction
A detailed look at meiosis
Where does variation come from?
Meiosis Defined
• Meiosis = the division of a diploid cell leading
to the production of haploid cells
• Overview:
http://www.youtube.com/watch?v=D1_mQS_FZ0
3. A detailed look at meiosis
So far, so good; looks like mitosis, right?
 SO, NOW WHAT?
 We have 2n chromosomes with 4n chromatids  2
rounds of cell division will give us 4 cells each with n
chromosomes
3. A detailed look at meiosis
FIRST CELL DIVISION =
“MEIOSIS I”
3. A detailed look at meiosis
FIRST CELL DIVISION = “MEIOSIS I”
2nd CELL DIVISION =
“MEIOSIS II”
LG 6,7,9,10,11,16
3. A detailed look at meiosis
SYNAPSIS!
Early in Meiosis I (Prophase I):
• Homologous chromosomes loosely pair up, aligned
gene by gene
• In crossing over, nonsister chromatids exchange
homologous DNA segments
( IMPORTANCE will become apparent soon…)
• Spindle attaches to centromeres
3. A detailed look at meiosis
Middle of Meiosis I (Metaphase I):
•Pairs of homologous chromosomes line up in the
middle of the cell plate, with one chromosome facing
each pole
13-8b
3. Fig.
A detailed
look at meiosis
Prophase I
Metaphase I
Centromere
Crossing over
Spindle
Homologous
chromosomes
Fragments
of nuclear
envelope
Microtubule
13-8c
3. Fig.
A detailed
look at meiosis
Telophase I and
Cytokinesis
Anaphase I
Sister chromatids
remain attached
Homologous
chromosomes
separate
Cleavage
furrow
With first cell division complete, Meiosis I ends
3. A detailed look at meiosis
• Meiosis II is very similar to mitosis
LG 7
13-8d
3. Fig.
A detailed
look at meiosis
Prophase II
Metaphase II
Anaphase II
Telophase II and
Cytokinesis
Sister chromatids
separate
at the end: 4 daughter cells, all haploid, all genetically different
Today’s Exit Ticket
MITOSIS
MEIOSIS
yes or no
yes or no
daughter cells genetically identical to
parent cell?
yes or no
yes or no
sister cells thus produced identical to
one another?
yes or no
yes or no
yes or no
yes or no
preceded by replication of
chromosomes?
# of rounds of cell division
# of daughter cells
# of chromosomes in daughter cells
compared to parent cell
happens in diploid cells, haploid cells,
both, or neither?
crossing over (synapsis)?