Mitosis and Meiosis

1
Mitosis and Meiosis

• Chapter 12 13
• Mitosis Meiosis

2
Next Unit Genetics DNA

• Chapter 12 13 Mitosis Meiosis
• Chapter 14 Principles of Heredity
• Chapter 15 Human Genetics Disorders
• Chapter 16 DNA History, Structure Function
• Three Labs will be done for this Unit
• Goal to complete before Thanksgiving

3
Introductory Questions 1

• 1) How do chromosomes differ from chromatin?
• 2) How many genes are thought to be contained on
  one chromosome?
• 3) How is every species different in regards to
  their chromosomes?
• 4) Name the three main stages of the cell cycle.
  
• 5) What are the four stages of mitosis? Which
  stage is the longest and which stage is the
  shortest?
• 6) Give three specific events that occur during
  prophase.
• 7) What is the end result of mitosis?

4
Significance of Understanding Mitosis

• Preserves the continuity of life
• Allows organisms to grow, repair, and reproduce
• Important in unlocking the mysteries of embryonic
  development stem cells
• Important in understanding how cancer develops
  and could someday provide clues in stopping
  cancer.

5

• Cell replacement (seen here in skin)

Deadcells
Epidermis, the outer layer of the skin
Dividingcells
Dermis
Figure 8.11B
6
Cells from an onion Root tip

• When the cell cycle operates normally, mitotic
  cell division functions in
• Growth (seen here in an onion root)

Figure 8.11A
7

• E. coli dividing

Figure 8.3x
8

• Asexual reproduction (seen here in a hydra)

Figure 8.11C
9
Mitosis

• Occurs only in certain types of cells
• Form of asexual reproduction
• Produces two genetically identical cells from one
  cell.
• The splitting or dividing of the nucleus
• Viewed in different stages by examining
  chromosome formation and behavior.

10
THE EUKARYOTIC CELL CYCLE AND MITOSIS

• A eukaryotic cell has many more genes than a
  prokaryotic cell
• The genes are grouped into multiple chromosomes,
  found in the nucleus
• The chromosomes of this plant cell are stained
  dark purple

Figure 8.4A
11
Chromosomes

• Condensed DNA attached to proteins
• Can only be seen when a cell is actively
  undergoing mitosis.
• Typical humans form 46 chromosomes vs. other
  organisms which varies significantly.
• Our 46 chromosomes are thought to contain
  anywhere from 25,000 to 100,000 genes.
• Duplicated before mitosis occurs producing a
  sister chromatid (identical copy)
• Sister chromatids held together by Centromere

12

• Human male bands

Figure 8.19x3
13

• Human female karyotype

Figure 8.19x2
14
Packaging of Genetic Materialhttp//www.biostudio
.com/demo_freeman_dna_coiling.htm

• Structure / Activity Diameter
• DNA smallest structure about (2 nm)
• DNA Histones Nucleosome (10 nm)
• Chromatin Fibers (30 nm)
• Extensive Looping (300 nm)
• Further Condensing (700 nm)
• Fully Formed Chromosome (1400 nm)

15
Sister chromatids

• Before a cell starts dividing, the chromosomes
  are duplicated

Centromere

• This process produces sister chromatids

Figure 8.4B
16

• When the cell divides, the sister chromatids
  separate

Chromosomeduplication
Sister chromatids
Centromere

• Two daughter cells are produced
• Each has a complete and identical set of
  chromosomes

Chromosomedistributiontodaughtercells
Figure 8.4C
17
INTERPHASE
PROPHASE
Figure 8.6
18
METAPHASE
TELOPHASE AND CYTOKINESIS
ANAPHASE
Cleavagefurrow
Nucleolusforming
Metaphaseplate
Nuclearenvelopeforming
Spindle
Daughterchromosomes
Figure 8.6 (continued)
19
The Cell Cycle Generation Time

• Interphase most of a cells life (90)
• -G1 1st gap of growth
• -S phase DNA is duplicated
• (synthesized)
• -G2 phase 2nd gap of growth
• Mitosis splitting of the nucleus (PMAT)
• Cytokinesis separation of the cytoplasm

20
The cell cycle multiplies cells

• The cell cycle consists of two major phases
• Interphase, where chromosomes duplicate and cell
  parts are made
• The mitotic phase, when cell division occurs

Figure 8.5
21
Interphase
22
Interphase

• Cells spend most of its time in this phase
• Cells are growing
• DNA has to be replicated (all 2 meters of it)
• Proteins are being produced
• 90 of all cells are in this phase
• Three phases G1, S, and G2

23
Prophase
24
Prophase

• Chromatin thickens (coils) into chromosomes
• Two copies of DNA are present sister chromatids
  (twice the amount of DNA is present)
• Centrioles replicate forming another centrosome
  separate.
• Centrioles separate to each side of the nucleus
• Nuclear membrane (envelope) disappears
• Microtubules elongate forming the spindle
  apparatus

25
Metaphase
26
Metaphase

• Chromosomes align themselves up in the center of
  the cell
• Spindle fibers (microtubules) attach to the
  centromere of the chromosomes
• Shortest phase of Mitosis (anaphase ?)

27
Metaphase
28

• Mitotic spindle

Figure 8.6x2
29
Anaphase - Early Late
30
Anaphase

• Chromosomes separate by the shortening of the
  microtubules.
• The sister chromatids separate to each side
  (pole) of the cell. (humans 46 to each side)
• The centrosome is located at each side of the
  cell.

31
Telophase (Plant Animal)
32
Cytokinesis Plant vs Animal Cells

• Cleavage furrow animals cells
• Cell plate Plant cells

33
Cytokinesis differs for plant and animal cells

• In animals, cytokinesis occurs by cleavage
• This process pinches the cell apart

Cleavagefurrow
Cleavagefurrow
Contracting ring ofmicrofilaments
Figure 8.7A
Daughter cells
34
Cell plateforming
Wall ofparent cell
Daughternucleus

• In plants, a membranous cell plate splits the
  cell in two

Cell wall
New cell wall
Vesicles containingcell wall material
Cell plate
Daughtercells
Figure 8.7B
35
Cells from an onion Root tip

• When the cell cycle operates normally, mitotic
  cell division functions in
• Growth (seen here in an onion root)

Figure 8.11A
36

• Mitosis collage, light micrographs

Figure 8.6x1
37
Whitefish-phases of Mitosis
38
Various phases of Mitosis-Plants
39
Which Phase is this?
40

• Sea urchin development

Figure 8.0x
41

• Cell cycle collage

Figure 8.5x
42

• Fibroblast growth

Figure 8.8x
43
Introductory Questions 1

• 1) How do chromosomes differ from chromatin?
• 2) How many genes are thought to be contained on
  one chromosome?
• 3) How is every species different in regards to
  their chromosomes?
• 4) Name the three main stages of the cell cycle.
  
• 5) What are the four stages of mitosis? Which
  stage is the longest and which stage is the
  shortest?
• 6) Give three specific events that occur during
  prophase.
• 7) What is the end result of mitosis?

44
Total Class Data for all Three Classes Fall 2005
45
Total Class Data for all Three Classes Fall 2006
46
Regulation of Cell Division

• Driven by specific molecular signals
• Research has shown
• Two cells in different phases causes the other to
  be pushed into the next phases.
• Ex.
• S phase G1 grown together will cause the G1
  cell to enter into the S phase immediately
• M phase cell G1 cell will cause the G1 cell to
  enter into the M phase immediately.
• There is an obvious control system in place.

47
Regulating Mitosis-Control System(pg. 229-231)

• Most cells can divide up to 50 times
• Control of the Cell cycle involves three
  checkpoints
• -G1 (most important checkpoint) restriction
  point
• (G0 non-dividing state)
• -G2
• -M phase
• Growth factors (proteins) Cyclins Kinases
• Kinases phosphorylate proteins, gives the go
  ahead
• Cdk are kinases that must be attached to a
  cyclin to be activated
• MPF Maturation promoting factor (Fig pg. 230)
• Complex of kinase and cyclin
• Triggers the passage from G2 phase into M phase
• peaks during Metaphase
• Telomeres-repeated sequences of DNA on tips of
  chromosomes

48
Growth factors signal the cell cycle control
system

• Proteins within the cell control the cell cycle
• Signals affecting critical checkpoints determine
  whether the cell will go through a complete cycle
  and divide

G1 checkpoint
Controlsystem
M checkpoint
Figure 8.9A
G2 checkpoint
49
Cyclin MPF Concentrations
50
Cyclin Kinase effects on the cell cycle.

• Animated link http//nobelprize.org/educational_g
  ames/medicine/2001/cellcycle.html

51

• The binding of growth factors to specific
  receptors on the plasma membrane is usually
  necessary for cell division

Growth factor
Plasma membrane
Relayproteins
G1 checkpoint
Receptor protein
Signal transduction pathway
Cell cyclecontrolsystem
Figure 8.8B
52
Mitotic Clock Mechanisms in CellsTelomeres,
Proteins, Cell size (SA), hormones, Growth
factors

• Telomeres Segments of DNA (200 repeated
  sequences of nucleotides) are lost at the tips of
  the chromosomes with each mitotic event.
• (Mitotic clock) the tips of chromosomes wear down
  and lose DNA sequences over time.
• Six Nucleotide sequence repeated hundreds of
  times
• 1,200 nucleotides are removed after each mitotic
  event

53
Image of Telomeres-notice light Blue Regions
54
Chromosomes in green Telomeres in yellow
55
Anchorage, cell density, and chemical growth
factors affect cell division

• Most animal cells divide only when stimulated,
  and others not at all
• In laboratory cultures, most normal cells divide
  only when attached to a surface
• They are anchorage dependent

56

• Cells continue dividing until they touch one
  another

• This is called density-dependent inhibition

Cells anchor to dish surface and divide.
When cells have formed a complete single layer,
they stop dividing (density-dependent inhibition).
If some cells are scraped away, the remaining
cells divide to fill the dish with a single layer
and then stop (density-dependent inhibition).
Figure 8.8A
57

• Growth factors are proteins secreted by cells
  that stimulate other cells to divide

See pg. 232
After forming a single layer, cells have stopped
dividing.
Providing an additional supply of growth factors
stimulates further cell division.
Figure 8.8B
58

• Malignant tumors can invade other tissues and may
  kill the organism

Lymphvessels
Tumor
Glandulartissue
Metastasis
1
2
3
A tumor grows from a single cancer cell.
Cancer cells invade neighboring tissue.
Cancer cells spread through lymph and blood
vessels to other parts of the body.
Figure 8.10
59
Growing out of control, cancer cells produce
Malignant tumors

• Cancer cells have abnormal cell cycles
• They divide excessively and can form abnormal
  masses called tumors
• Radiation and chemotherapy are effective as
  cancer treatments because they interfere with
  cell division

60

• Breast cancer cell

Figure 8.10x1
61

• Mammograms

Figure 8.10x2
62
Anti-Cancer drugs

• Colchicine blocks microtubules from forming
• -binds inhibits unpolymerized tubulin
• -breakdown of microtubules occur
• -polyploidy could occur
• Taxol Found in the bark of yew trees
• -blocks ovarian cancer from forming
• http//www.ncl.ox.ac.uk/quicktime/taxol.html

63
Growth Factors that stimulate Cell Division

• PDGF Platelet-derived growth factor causes
  fibroblasts to divide in response to an injury.
  Has been shown to be effective in artificial
  conditions
• Cytokinins key hormone in plants that promotes
  cell division

64
Genes that are thought to cause CancerSee Pgs
371-372

• Oncogenes a gene that increases cell division
  and triggers cancerous characteristics.
• Tumor Suppressor genes a gene that inactivates
  or inhibits cell division. Prevents uncontrolled
  cell growth (cancer). It keeps mitosis in check
  and controls the cell cycle.
• Failure of normal cell programmed death
  (Apotosis) Pgs. 800 902

65
Stem Cells (pgs. 415-418)

• Undifferentiated cells
• Progenitor cells partially specialized cell. an
  intermediate between a stem cell and a fully
  differentiated cell.
• Pluripotent cells follows fewer pathways that it
  can develop into.
• Totipotent cells cells that are very early in
  development when the zygote has developed into a
  small ball of cells.

66
Cell Differentiationhttp//learn.genetics.utah.ed
u/units/stemcells/whatissc/
67
Evolution of Mitosis
Chromosomes attach to the plasma membrane
Chromosomes attach to the nuclear membrane
Pass through the nucleus
Spindle forms within the nucleus
68
Introductory Questions 1

• 1) How do chromosomes differ from chromatin?
• 2) How many genes are thought to be contained on
  one chromosome?
• 3) How is every species different in regards to
  their chromosomes?
• 4) Name the three main stages of the cell cycle.
  
• 5) What are the four stages of mitosis? Which
  stage is the longest and which stage is the
  shortest?
• 6) Give three specific events that occur during
  prophase.
• 7) What is the end result of mitosis?

69
Introductory Questions 2

• 1) From our the overall data in our Mitosis lab,
  what stage was the shortest and which stage was
  the longest? If Telophase was supposed to be the
  shortest phase, what would have contributed to
  our different results?
• 2) Which phase is used to obtain pictures of
  chromosomes in order to generate a karyotype?
• 3) Give five differences between Mitosis and
  Meiosis.
• 4) Name three factors in Meiosis reproduction
  that contributes in increasing genetic
  variability within a population.
• 5) What is a polar body? How is oogenesis
  different from spematogenesis?
• 6) How is a sporophyte different from a
  gametophyte? What do they produce and what
  process is involved, mitosis or meiosis?
• 7) What is a tetrad? Which phase of Meiosis does
  crossing over occur?

70
Heredity, Life Cycles, and Meiosis Chapter 13
71
Heredity

• Heredity the transmission of traits from one
  generation to the next
• Asexual reproduction clones
• Sexual reproduction variation
• Human life cycle
• 23 pairs of homologous chromosomes
• 1 pair of sex chromosomes (X or Y)
• and 22 pairs of autosomes
• Karyotype Pix of chromosomes
• -Gametes are haploid (n)
• -All other cells (somatic) are diploid (2n)
• -Fertilization (syngamy) joining (fusion)
• of gametes to produce a zygote
• Meiosis cell division to produce haploid
  gametes

72

• The human life cycle

Haploid gametes (n 23)
Egg cell
Sperm cell
MEIOSIS
FERTILIZATION
Diploidzygote (2n 46)
Multicellulardiploid adults (2n 46)
Mitosis anddevelopment
Figure 8.13
73
Alternative Life Cycles

• Fungi/some algae
• -Meiosis produces haploid cells (n)
• that divide by mitosis to produce
• -Haploid (n) adults
• (gametes produced by mitosis)
• Plants/some algae
• Do Alternation of generations
• 2n Sporophyte generation
• n Gametophyte generation
• Meiosis occurs produces spores
• Spores are haploid (n)
• Spores divide by mitosis to generate more haploid
  cells (n)
• Gametes are produced by mitosis which then
  fertilize into a sporophyte (2n)

74

• Human female karyotype

Figure 8.19x2
75

• Human male karyotype

Figure 8.19x4
76
Meiosis

• Chromosome replicate
• 2 Cell divisions occur
• (Meiosis I Meiosis II)
• 4 daughter cells are made all are (n) haploid
• Homologous Chroms separate in meiosis I
• Meiosis II Mitosis
• (chromatids separate)

77
Homologous chromosomes carry different versions
of genes

• The differences between homologous chromosomes
  are based on the fact that they can carry
  different versions of a gene (alleles) at
  corresponding loci

78
Homologous Chromosomes(Are they identical?)
Tetrad (Bivalent)
? from father
from mother
Sister Chromatids
79
MEIOSIS I Homologous chromosomes separate
INTERPHASE
PROPHASE I
METAPHASE I
ANAPHASE I
Centrosomes(withcentriolepairs)
Microtubules attached tokinetochore
Metaphaseplate
Sister chromatidsremain attached
Sites of crossing over
Spindle
Nuclearenvelope
Sisterchromatids
Tetrad
Centromere(with kinetochore)
Homologouschromosomes separate
Chromatin
Figure 8.14, part 1
80
Crossing over further increases genetic
variability

• Crossing over is the exchange of corresponding
  segments between two homologous chromosomes
• Genetic recombination results from crossing over
  during prophase I of meiosis

81
Tetrad
Chaisma
Centromere
Figure 8.18A
82
Synaptonemal Complex- Pg 213

• Protein that hold homologous chromosomes together
  
• Thought to be involved in crossing over events

83
Coat-colorgenes
Eye-colorgenes

• How crossing over leads to genetic recombination

Tetrad(homologous pair ofchromosomes in
synapsis)
1
Breakage of homologous chromatids
Joining of homologous chromatids
2
Chiasma
Separation of homologouschromosomes at anaphase I
3
Separation of chromatids atanaphase II and
completion of meiosis
4
Parental type of chromosome
Recombinant chromosome
Recombinant chromosome
Parental type of chromosome
Figure 8.18B
Gametes of four genetic types
84
Coat-color genes
Eye-color genes
C
E
Brown
Black
C
E
C
E
c
e
c
e
c
e
White
Pink
Tetrad in parent cell(homologous pair
ofduplicated chromosomes)
Chromosomes ofthe four gametes
Figure 8.17A, B
85
Origins of Genetic Variation

• (1) Independent assortment
• How they line up during metaphase I
• Matters!!!
• Homologous pairs of chromosomes
• position and orient themselves
• Randomly. (random positioning)
• Different combinations are possible when gametes
  are produced.

86
POSSIBILITY 1
POSSIBILITY 2
Two equally probable arrangements of chromosomes
at metaphase I
Metaphase II
Gametes
Combination 1
Combination 2
Combination 3
Combination 4
Figure 8.16
87
Origins of Genetic Variation

• (2) Crossing over (prophase I)
• -the reciprocal exchange of
• genetic material between
• nonsister chromatids during
• synapsis of meiosis I
• (recombinant chromosomes)
• (3) Random fertilization
• 1 sperm (1 of 8 million possible chromosome
  combinations) x 1 ovum (1 of 8 million different
  possibilities) 64 trillion diploid combinations!

88
MEIOSIS II Sister chromatids separate
TELOPHASE IAND CYTOKINESIS
TELOPHASE IIAND CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
Cleavagefurrow
Sister chromatidsseparate
Haploiddaughter cellsforming
Figure 8.14, part 2
89
Meiosis vs. Mitosishttp//www.pbs.org/wgbh/nova/b
aby/divi_flash.html

• Synapsis/tetrad/chiasmata (prophase I)
• Homologous vs. individual chromosomes (metaphase
  I)
• Sister chromatids do not separate (anaphase I)
• Meiosis I separates homologous pairs of
  chromosomes, not sister chromatids of individual
  chromosomes.

90
MITOSIS
MEIOSIS
PARENT CELL(before chromosome replication)
Site ofcrossing over
MEIOSIS I
PROPHASE I Tetrad formedby synapsis of
homologous chromosomes
PROPHASE
Chromosomereplication
Chromosomereplication
Duplicatedchromosome(two sister chromatids)
2n 4
Chromosomes align at the metaphase plate
Tetradsalign at themetaphase plate
METAPHASE I
METAPHASE
ANAPHASE I TELOPHASE I
ANAPHASETELOPHASE
Sister chromatidsseparate duringanaphase
Homologouschromosomesseparateduringanaphase
Isisterchromatids remain together
Haploidn 2
Daughtercells of meiosis I
No further chromosomal replication sister
chromatids separate during anaphase II
2n
2n
MEIOSIS II
Daughter cellsof mitosis
n
n
n
n
Daughter cells of meiosis II
Figure 8.15
91
Introductory Questions 2

• 1) From our the overall data in our Mitosis lab,
  what stage was the shortest and which stage was
  the longest? If Telophase was supposed to be the
  shortest phase, what would have contributed to
  our different results?
• 2) Which phase is used to obtain pictures of
  chromosomes in order to generate a karyotype?
• 3) Give five differences between Mitosis and
  Meiosis.
• 4) Name three factors in Meiosis reproduction
  that contributes in increasing genetic
  variability within a population.
• 5) What is a polar body? How is oogenesis
  different from spematogenesis?
• 6) How is a sporophyte different from a
  gametophyte? What do they produce and what
  process is involved, mitosis or meiosis?
• 7) What is a tetrad? Which phase of Meiosis does
  crossing over occur?

92

• Translocation

Figure 8.23Bx
93

• At fertilization, a sperm fuses with an egg,
  forming a diploid zygote

• Repeated mitotic divisions lead to the
  development of a mature adult
• The adult makes haploid gametes by meiosis
• All of these processes make up the sexual life
  cycle of organisms

94

• The large number of possible arrangements of
  chromosome pairs at metaphase I of meiosis leads
  to many different combinations of chromosomes in
  gametes

• Random fertilization also increases variation in
  offspring

95

• Human female bands

Figure 8.19x1
96

• Human female karyotype

Figure 8.19x2
97

• Human male bands

Figure 8.19x3
98

• Human male karyotype

Figure 8.19x4
99

• Down syndrome karyotype

Figure 8.20Ax
100

• Klinefelters karyotype

Figure 8.22Ax
101

• XYY karyotype

Figure 8.22x