fall 2005 – @ k. malone ch. 10, cell growth and division ch. 11, meiosis (sec. 11-4) ch. 10:...
TRANSCRIPT
Fall 2005 – @ K. Malone
Ch. 10, Cell Growth and Division
Ch. 11, Meiosis (sec. 11-4)
• Ch. 10:– Cell Growth- why do cells divide instead
of continue to grow?– Cell Division – Cell Cycle and when a cell
divides, Mitosis– Regulation of the Cell Cycle- how it’s
controlled, what happens when it’s out of control
• Ch. 11:– Phases of Meiosis– Comparing Mitosis and Meiosis
Fall 2005 – @ K. Malone
Section 10.1 – Cell GrowthCell Growth
• How do organisms grow? Do their cells get bigger? Or do they make more cells?
• Answer = Make more cells!!!• There is a limit to how big cells can grow!• Getting bigger does 2 things:1. Places more demands on DNA2. Makes it harder to move molecules across a
cell’s membrane
Just right
TooSmall
Too Big!
I’m out I’m out of of
controlcontrol!!
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Understanding the relationship between a cell’s Understanding the relationship between a cell’s Surface AreaSurface Area and and VolumeVolume is the key to understanding why cells is the key to understanding why cells mustmust divide divide
as they grow.as they grow.
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Surface Area to Volume Ratio
1 cm1 cm
1 1 cmcm
1 cm1 cm
6 sided cube6 sided cube
Volume (V):Volume (V): 1 x 1 x 1 = 1 x 1 x 1 = 1 1 cmcm33 (length x width x height)Ratio of SA to V:Ratio of SA to V: 6/1 = 6/1 = 6:16:1
Bigger 6 sided cubeBigger 6 sided cube
3 cm3 cm
3 cm3 cm
3 cm3 cm
SA:SA: 3 x 3 x 6 = 54 cm3 x 3 x 6 = 54 cm33
V:V: 3 x 3 x 3 = 27 cm3 x 3 x 3 = 27 cm33
Ratio of SA to V: 54/27 = 2:1Ratio of SA to V: 54/27 = 2:1
More More surface surface
area! Good!area! Good!
Less surface Less surface area! Bad!area! Bad!
Bigger is NOT better
!
Surface Area (SA): Surface Area (SA): 1 x 1 x 6 1 x 1 x 6 = = 6 cm6 cm33
(length x width x height x # sides)
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Volume increases more rapidly than Surface Area and this causes the ratio
of SA to V to decrease.
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Decreasing the SA to V ratio causes big problems for the cell.
More molecules trying to go through the membrane (SA)
and there’s less surface area for everything to move through!
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What’s the solution to this traffic problemWhat’s the solution to this traffic problem??
Instead of growing bigger, Instead of growing bigger, let’s make more cells! let’s make more cells!
And to do this, And to do this, 1 cell will divide into 2 cells.1 cell will divide into 2 cells.
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Cell Division• When a cell divides, the 2 cells that result are called “daughter”
cells• Cell Division = process by which a cell divides into 2 new
daughter cells• Before cell division, the cell replicates, or makes
copies of all of its DNA
• Solves the 2 problems with cell growth:• New daughter cells get one complete set of genetic
information- they get their own complete genetic library
• No more problems with SA to V ratio because daughter cells has an increased ratio of SA to V because their volume overall is reduced (one cell dividing into two makes both cells smaller)
I’m too fat
daughter daughter
Mommy?
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Cell Division• In Eukaryotes (you!), cell division occurs in 2 main
stages:1. Mitosis = division of the cell’s nucleus2. Cytokinesis = division of the cytoplasm
Section 10-2
(Sy-toh-kih-NEE-sis)
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Genetic information passed from 1 Genetic information passed from 1 generation to the next is carried by generation to the next is carried by ChromosomesChromosomes
ChromosomesChromosomes are made up of are made up of DNADNA- the - the part that carries the cell’s genetic part that carries the cell’s genetic informationinformation
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Mitosis is considered asexual because cells produced by it are genetically identical to the parent cell. Box
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chromatid
replication
Chromosomes
• When a cell isn’t in the process of dividing, chromosomes are not visible because they are spread out within the nucleus.
• However, when cell division is beginning, the chromosomes condense into compact, visible structures we can see in a microscope.
• Before cell division occurs, each chromosome is copied, or replicated, and the identical copies are called “sister” chromatids (KROH-muh-tids)
LYLAS!
Yo! Sis!
Sister chromatidSister chromatid
Centromere
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The Cell Cycle• The Cell Cycle is a series of events that cells
go through as they grow and divide 1. Cell grows2. Cell prepares for division3. Cell divides to form 2 daughter cells (each daughter cell will begin the cell cycle again)
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Cell Cycle consists of 4 Cell Cycle consists of 4 phases:phases:
1.1. Mitosis and CytokinesisMitosis and Cytokinesis = = MM phase phase
2.2. Growth phaseGrowth phase = G = G11 (“G” = (“G” = gap)gap)
3.3. Chromosome replicationChromosome replication = = S phaseS phase
4.4. Preparation for mitosis Preparation for mitosis = = GG22
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Interphase = “in between” period of growth for a cell
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Cell Cycle Phases
M phase
G2 phase
G1 phase
S ph
ase
IM I
I
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S phase = when chromosomes are replicated and synthesis of DNA molecules occurs
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G2 phase = when cells make many organelles and molecules needed for cell division
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M phase = when cell division occurs
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G1 phase = when cells do most of their growing- cells increase in size and make new proteins and organelles
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Mitosis
• Interphase then….• Mitosis has 4 phases:
• 1. Prophase• 2. Metaphase• 3. Anaphase• 4. Telophase
I then ..PMATI then ..PMAT
Interphase is NOT part of Mitosis!!!!! Remember that!
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Mitosis
InterphaseInterphase
Centrioles
ChromatinNuclear envelope
Interphase = cell grows and replicates its DNA and centrioles.
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InterphaseInterphase
Centrioles
ChromatinNuclear envelope
Interphase = cell grows and replicates its DNA and centrioles.
Spindle forming
Chromosomes (paired chromatids)
Prophase = chromatin condenses into chromosomes, centrioles separate, spindle forms, nuclear envelope breaks down
ProphaseProphase
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Centromere
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InterphaseInterphase
Centrioles
ChromatinNuclear envelope
Interphase = cell grows and replicates its DNA and centrioles.
Spindle forming
Chromosomes (paired chromatids)
Centromere
Prophase = chromatin condenses into chromosomes, centrioles separate, spindle forms, nuclear envelope breaks down.
ProphaseProphase
Centriole
Spindle
Centriole
MetaphaseMetaphase
Metaphase = chromosomes line up across the center of the cell, each chromosome is connected to a spindle fiber at its centromere
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InterphaseInterphase
Centrioles
ChromatinNuclear envelope
Interphase = cell grows and replicates its DNA and centrioles.
Spindle forming
Chromosomes (paired chromatids)
Centromere
Prophase = chromatin condenses into chromosomes, centrioles separate, spindle forms, nuclear envelope breaks down.
ProphaseProphase
Centriole
Spindle
Centriole
MetaphaseMetaphaseIndividual chromosomes
AnaphaseAnaphase
Anaphase = sister chromatids separate into individual chromosomes and move apart
Metaphase = chromosomes line up across the center of the cell, each chromosome is connected to a spindle fiber at its centromere
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InterphaseInterphase
Centrioles
ChromatinNuclear envelope
Interphase = cell grows and replicates its DNA and centrioles.
Spindle forming
Chromosomes (paired chromatids)
Centromere
Prophase = chromatin condenses into chromosomes, centrioles separate, spindle forms, nuclear envelope breaks down.
ProphaseProphase
Centriole
Spindle
Centriole
MetaphaseMetaphaseIndividual chromosomes
AnaphaseAnaphase Anaphase = sister chromatids separate into individual chromosomes and are moved apart
Nuclear envelope reforming
TelophaseTelophase
Telophase = chromosomes gather at opposite ends of the cell and lose their distinct shapes- 2 new nuclear envelopes form
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TelophaseTelophase
InterphaseInterphase
Centrioles
ChromatinNuclear envelope
Interphase = cell grows and replicates its DNA and centrioles.
Spindle forming
Chromosomes (paired chromatids)
Centromere
Prophase = chromatin condenses into chromosomes, centrioles separate, spindle forms, nuclear envelope breaks down.
ProphaseProphase
Centriole
Spindle
Centriole
MetaphaseMetaphaseIndividual chromosomes
AnaphaseAnaphase
Anaphase = sister chromatids separate into individual chromosomes and are moved apart
Nuclear envelope reforming
Telophase = chromosomes gather at opposite ends of the cell and lose their distinct shapes- 2 new nuclear envelopes form
Cytokinesis
Cytokinesis = cytoplasm pinches in ½ , each daughter cell has an identical set of chromosomes
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TelophaseTelophase
InterphaseInterphase
Interphase = cell grows and replicates its DNA and centrioles.
Prophase = chromatin condenses into chromosomes, centrioles separate, spindle forms, nuclear envelope breaks down.
MetaphaseMetaphase
AnaphaseAnaphase
Anaphase = sister chromatids separate into individual chromosomes and are moved apart
Telophase = chromosomes gather at opposite ends of the cell and lose their distinct shapes- 2 new nuclear envelopes form
CytokinesisCytokinesis
Cytokinesis = cytoplasm pinches in half, each daughter cell has an identical set of duplicate chromosomes
ProphaseProphase
Metaphase = chromosomes line up across the center of the cell, and each is connected to a spindle fiber at its centromere
I…then PMATI…then PMAT
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Interphase Metaphase
Prophase
Anaphase
Telophase
Cytokinesis
Product of Mitosis?2 identical daughter cells
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Cell Cycle Tree Map
InterphaseInterphaseis divided into…is divided into…
MitosisMitosisis divided into…is divided into…
GG11 phase phase S phaseS phase GG22 phase phase ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase TelophaseTelophase
Cell CycleCell Cycleincludes…..includes…..
And then………Cytokinesis
Fall 2005 – @ K. Malone
Title: The Cell Cycle and MitosisYour Name: ex. by Fred Cooks
1st : The Cell Cycle & Interphase
2nd : Mitosis - Prophase
3rd : Mitosis - Metaphase
4th : Mitosis - Anaphase
5th : Mitosis - Telophase
P
M
A
T
6th : Cytokinesis
Draw the cell cycle diagram on pg. Label the parts. List the stages of the cell cycle, describe what happens in each stage (G1, G2, S and M)Prophase. Draw a cell in prophase using pg. 246 as a reference. List 3 facts describing events in Prophase.Metaphase. Draw a cell in metaphase, and list 3 facts describing events in this phase.
Cytokinesis. Draw a cell in cytokinesis and define what happens to the cell.
Anaphase and Telophase. Draw a cell in anaphase and telophase, and list 3 facts describing events in each phase.
Chromosome CentromereCentriole SpindleSister chromatids
Include these definitions:
Fall 2005 – @ K. Malone
Regulation of the Cell Cycle
• For very obvious reasons, the cell cycle is a tightly, highly controlled process.
• Do you know why?
• Uncontrolled cell growth is cancer!!! Cancer can be deadly!
• Not all cells need to divide all the time, or at all.
• There is a time and place for cell division, and controlling the cell cycle is important because it is part of homeostasis- keeping an organism alive and healthy.
Section 10-3
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Controls on Cell Division
In the lab, scientists can grow cells by placing them in a petri dish, along with nutrients.
Cells will grow until they form a single layer covering the bottom of the dish, then they stop growing when they come into contact with one another.
These experiments show that controls on cell growth and division can be turned onon and offoff.
If you remove cells from the center of the dish, cells bordering the open space begin dividing and filling the empty space.
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What happens in your body?
• Similar processes happen in your own body.
• What if you get a cut on your finger? A broken bone?
• When you’re injured, cells at the edge of the cut or break are stimulated to divide rapidly and produce new cells, starting the process of healing.
• When the gap is repaired, the controls for cell division turn off again, and everything returns to normal.
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Cell Cycle Regulators
• Tim Hunt and Mark Kirschner found a protein that, when injected into non-dividing cells, would cause mitotic spindle fibers to form.
• Levels of this protein rose and fell, depending on the phases of the cell cycle – produced when needed for division, not produced when no cell division is occurring.
• They called the protein Cyclin (for cycle)• Cyclins = regulate the timing of the Cell Cycle
in Eukaryote cells (your cells!)
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Hunt and Kirschner’s Experiment
The reason for this effect is the protein Cyclin, which triggers cell division in non-dividing cells.
A sample of cytoplasm is removed from a cell in mitosis.
The sample is injected into a second cell in G2 of interphase.
As a result, the second cell enters mitosis.
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Internal and External Regulators
• Internal regulators = regulating proteins that respond to events inside the cell, and control the cell cycle; allow cell cycle to proceed only when certain process have happened inside the cell.
• Similar to: You can’t eat your dessert until you clean your plate!
• External regulators = regulating proteins that respond to events outside the cell, and control the cell cycle
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Uncontrolled Cell Growth
• Cancer.• Such a scary word, isn’t it?• Most common cancers:• Men: Prostate cancer (33%)
Lung (13%)• Women: Breast (32%)
Lung (13%)
Affects 1 in 6 men
Affects 1 in 13 men
Affects 1 in 7 women
Affects 1 in 17 women
Pretty frightening,
yes?
American Cancer Society 2004 Statistics
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44.77% chance of a man getting cancer44.77% chance of a man getting cancer33.08% chance of a woman getting cancer33.08% chance of a woman getting cancer
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Cancer• Cancer cells do not respond to the signals that
regulate growth of most cells.• They divide uncontrollably and form masses of cells
called Tumors that can damage the surrounding tissues.
Untreated Breast CancerUntreated Breast Cancer Tumor on the eyeTumor on the eye
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Tumors = masses of uncontrollably dividing cells that damage surrounding tissues
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•Cancer cells may Metastasize, or break loose and spread throughout the body.
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Cancer• Cancer is a disease of the Cell Cycle.
• To find a cure for this horrible disease, we must first deeply and completely understand the Cell Cycle, what regulates it, and how it can go wrong, resulting in cancer.
• This is a major scientific challenge, but at least we know now where to start searching for a cure- the Cell Cycle.
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Stem Cells• When you were first conceived, you started out as a
SINGLE cell. One cell. • That one cell then divided over and over, (Mitosis)
producing cells that could and would become all the specialized parts of your body.
• Fetal Stem Cells= the cells in the earliest stages of fetal (baby) development, they can potentially become any cell type in the body.
• Adult Stem Cells = usually found in the bone marrow, can be induced (pushed) to become other cell types like muscle, nerve and liver cells
Controversial – Unethical?
Has the promise to repair many injuries and replace damaged organs (ex. liver)
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Meiosis
• Humans have 46 chromosomes in every cell of our bodies except the sex cells or gametes (eggs and sperm)- they have 23 chromosomes
• When a baby is conceived, an egg from mom and a sperm from dad, combine into the first cell of the new baby. 23+23 = 46
Section 11-4
What would happen if the What would happen if the egg and sperm both had 46 egg and sperm both had 46 chromosomes?chromosomes?Baby would have Baby would have 9292 chromosomes!! Disaster!chromosomes!! Disaster!
46 46
92chromosomes
= death, disease
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Remembering Meiosis
• Mitosis is a process that occurs in almost every cell of your body (body cells), except the sex cells, or gametes.
• Mitosis = My toe sis, it happens in your toes!
• Meiosis is a process of cell division that doesn’t happen in your toes, it only happens in your sex cells, gametes
• Meiosis = My OH! Sis (as in uh-oh!)
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Meiosis• To solve this problem, the cells in the gametes (eggs
and sperm), undergo Meiosis instead of Mitosis, when they divide.
• Why Meiosis?
• Most cells in our body are Diploid (“di” = 2)• Diploid = have 2 sets of chromosomes, 2n
(one from mom, one from dad)• Sex cells, or gametes, are Haploid • Haploid = have 1 set of chromosomes, 1n
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Meiosis results in cells with ½ the # of chromosomes, so they can combine in sexual
reproduction, which results in an embryo with the normal amount of chromosomes.
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Chromosome Number
• An example.
• Fruit Flies (Drosophila), have 8 chromosomes total – 4 from dad fruit fly, 4 from mom fruit fly.
Diploid number?2n = 8
Haploid number?
1n = 4
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Homologous chromosomes= 2 sets of similar chromosomes, one from mom, one from dad
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Phases of Meiosis
• How are haploid (1n) gamete cells produced from diploid (2n) cells?
• By Meiosis (my-OH-sis)
• Meiosis = process of reduction cell division where the # of chromosomes per cell is cut in ½ by the separation of homologous chromosomes
Homologous = same chromosome, it just comes from different parents (mom or dad)
Meiosis involves 2 distinct divisions, 1. Meiosis I 2. Meiosis II Results of Meiosis? = cells with a haploid (1n)
number of chromosomes
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Meiosis I
Chromosome duplicationChromosome duplication
2 sister chromatids2 sister chromatids
4 sister chromatids 4 sister chromatids form a Tetradform a Tetrad
Interphase I Prophase I
Interphase I = Cells undergo a round of DNA replication, forming duplicate chromosomes
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Prophase I = Each chromosome pairs up with its matching homologous chromosome forming a tetrad
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Tetrads= in prophase I, chromosomes duplicate and form a structure with 4 chromosomes (tetrad)
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During prophase I of Meiosis, when the tetrads form, a phenomenon called “Crossing Over” can occur.
Owww! My
arm!
Sorry!
Who me?
Hey hot stuff, wanna dance?
I think he likes
me!
You got chocolate in my peanut
butter!
You got peanut butter
in my chocolate!
Help!Crossing Over = results in the exchange of genetic information between homologous chromosomes
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Meiosis I
Interphase I Prophase I Metaphase I
Interphase I = Cells undergo a round of DNA replication, forming duplicate chromosomes
Prophase I = Each chromosome pairs up with its corresponding homologous chromosome to form a tetrad
Anaphase I = Fibers pull the homologous chromosomes towards opposite ends of the cell (“A” for apart)
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Metaphase I = Spindle fibers attach to the chromosomes, then they line up in the middle (“M” for middle)
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Anaphase I
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Meiosis I
Interphase I Prophase I Metaphase I Anaphase I Telophase and Cytokinesis
Prophase I = Each chromosome pairs up with its corresponding homologous chromosome to form a tetrad
Interphase I = Cells undergo a round of DNA replication, forming duplicate chromosomes
Anaphase I = Fibers pull the homologous chromosomes towards opposite ends of the cell (“A” for apart)
Metaphase I = Spindle fibers attach to the chromosomes, then they line up in the middle (“M” for middle)
Telophase I and Cytokinesis = Nuclear membranes form, the cell separates into 2 new cells
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Meiosis IIThe 2 new cells now enter a 2nd round of meiotic division
No more chromosome duplication
prophase II
Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell Box
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Meiosis II
prophase II metaphase II
Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell
Metaphase II = chromosomes line up in the middle Box
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Meiosis II
anaphase II
1
2
3
4
telophase IIprophase II metaphase II
Metaphase II = chromosomes line up in the middle
Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell
Anaphase II = sister chromatids separate and move to opposite ends of the cell
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Telophase II and Cytokinesis = of meiosis II results in 4 haploid (1n) daughter cells
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Prophase I
Anaphase I
Telophase I&
Cytokinesis
Prophase II
IP
MA
T
P
MAT
I then …PMAT…..PMATI then …PMAT…..PMAT
Telophase II&
CytokinesisAnaphase II Metaphase II
4 daughter cells4 daughter cellswith haploid # (1n)with haploid # (1n)
Humans = 2n = 46
9292
92 92
46
46
464623
Flow Chart for MeiosisFlow Chart for Meiosis
Interphase I
Metaphase I
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Gamete Formation
• Why do we even have Meiosis?• To make gametes (eggs and sperm).• Male gametes = sperm• Female gametes = eggs
Why do we need eggs and sperm?Why do we need eggs and sperm?
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End of Chapter 10 and Chapter 11 Section 11-4
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For For Sexual ReproductionSexual Reproduction, where egg , where egg and sperm unite to make an embryoand sperm unite to make an embryo
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