Mitosis and Meiosis

• Chapter 12 & 13• Mitosis & Meiosis

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 and to take

Test #3 on 11/20 (Tuesday)

Video #1: Generations-Mitosis & Meiosis1. In the mid 1800’s what did Paseur, Lister do? In 1876, What did Walter

Flemming do that provided better visualization of parts in the cell? What did he see & discover?

2. Chromosomes literally mean: “_______”3. What is a centromere and what is its function?4. What is a karyotype and what does it reveal? What are “homologous

chromosomes”?5. How many chromosomes do humans, fruit flies (Drosophila), horsetails,

Toads, and pea plants have?6. Name the business used in the 2nd segment to show the importance of

mitosis. 7. Briefly explain what “grafting” is? 8. A complete cycle can be completed in about ______hrs in a rapidly

dividing tissue such as bone marrow. During this time mitosis occurs for only _______ hr(s). Pg. 221

9. Name the FOUR phases of Mitosis and two key events that occur. (See pg. 222-223)

10. Name two differences between Mitosis & Meiosis after watching the final segment.

****Write the Title for each segment and THREE key statements for each segment.

Introductory Questions #11) How much DNA does a typical human cell have?

How are chromosomes differ from chromatin?2) How is a somatic cell different from a gamete?3) How is every species different in regards to their

chromosomes? 4) Name the main stages of the cell cycle. (pg. 221)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) How are plant cell different from animal cells when

they divide?

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.

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.

• Cell replacement (seen here in skin)

Deadcells

Figure 8.11B

Dividingcells

Epidermis, the outer layer of the skin

Dermis

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)

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”

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

Cells from an onion Root tip

Figure 8.11A

• E. coli dividing

Figure 8.3x

• Asexual reproduction (seen here in a hydra)

Figure 8.11C

• 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

THE EUKARYOTIC CELL CYCLE AND MITOSIS

Figure 8.4A

• Human male bands

Figure 8.19x3

• Human female karyotype

Figure 8.19x2

• Before a cell starts dividing, the chromosomes are duplicated

– This process produces sister chromatids

Centromere

Sister chromatids

Figure 8.4B

• When the cell divides, the sister chromatids separate

– Two daughter cells are produced

– Each has a complete and identical set of chromosomes

Centromere Sister chromatids

Figure 8.4C

Chromosomeduplication

Chromosomedistribution

todaughter

cells

INTERPHASE PROPHASE

Figure 8.6

See Pgs 222-223

METAPHASE TELOPHASE AND CYTOKINESIS

Metaphaseplate

Spindle Daughterchromosomes

Cleavagefurrow

Nucleolusforming

Nuclearenvelopeforming

ANAPHASE

Figure 8.6 (continued)

The Cell Cycle: Generation Time

• Interphase: most of a cell’s 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

• The cell cycle consists of two major phases:– Interphase, where chromosomes duplicate

and cell parts are made

– The mitotic phase, when cell division occurs

The cell cycle multiplies cells

Figure 8.5

Interphase

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

Prophase

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

Metaphase

Metaphase• Chromosomes align themselves up in the

center of the cell

• Spindle fibers (microtubules) attach to the centromere of the chromosomes

• Longest phase of Mitosis

Metaphase

• Mitotic spindle

Figure 8.6x2

Anaphase - Early & Late

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.

Telophase (Plant & Animal)

Cytokinesis: Plant vs Animal Cells

• Cleavage furrow: animals cells

• Cell plate: Plant cells

• In animals, cytokinesis occurs by cleavage– This process pinches

the cell apart

Cytokinesis differs for plant and animal cells

Figure 8.7A

Cleavagefurrow

Cleavagefurrow

Contracting ring ofmicrofilaments

Daughter cells

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

Vesicles containingcell wall material

Cell plateforming

Figure 8.7BCell plate Daughter

cells

Wall ofparent cell

Daughternucleus

Cell wall New cell wall

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

Cells from an onion Root tip

Figure 8.11A

• Mitosis collage, light micrographs

Figure 8.6x1

Whitefish-phases of Mitosis

Various phases of Mitosis-Plants

Which Phase is this?

• Sea urchin development

Figure 8.0x

• Cell cycle collage

Figure 8.5x

• Fibroblast growth

Figure 8.8x

Total Class Data for all Three Classes: Fall 2005

Interphase Prophase Metaphase Anaphase TelophaseTotal # of cells 11806 2451 386 264 516% in each phase 77% 16% 3% 2% 3%Time in each phase (min) 1102.3 228.8 36.0 24.6 48.2Hours 18.4 3.8 0.6 0.4 0.8

Total Class Data for all Three Classes: Fall 2006

Interphase Prophase Metaphase Anaphase Telophase

Total # of cells 18296 1821 529 461 695% in each phase 84% 8% 2% 2% 3%Time in each phase (min) 1208.1 122.3 35.2 29.9 44.5Hours 20.1 2.0 0.6 0.5 0.7

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.

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

• Proteins within the cell control the cell cycle– Signals affecting critical checkpoints determine

whether the cell will go through a complete cycle and divide

Growth factors signal the cell cycle control system

G1 checkpoint

M checkpoint G2 checkpoint

Controlsystem

Figure 8.9A

Cyclin & Kinase effects on the cell cycle.

• Animated link: http://nobelprize.org/educational_games/medicine/2001/cellcycle.html

Introductory Questions #21) Which checkpoint in the regulation of mitosis is considered

the “restriction point”? Why point and not the others? 2) Name the two protein molecules that are high in

concentration during the mitotic (M) phase of the cell cycle. Name the complex that it forms.

3) Why are telomeres considered to be a “mitotic clock”?4) How are tumor supressor genes different from an

oncogene? What is the difference between a malignant tumor and a benign tumor?

5) When looking at the hypothetical sequence of how mitosis may have evolved how is the process different in a bacteria and diatom from a plant and animal cell?

Cyclin & MPF Concentrations

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

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

Growth factor

Figure 8.8B

Cell cyclecontrolsystem

Plasma membrane

Receptorprotein

Signal transduction pathway

G1 checkpointRelayproteins

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

Image of Telomeres-notice light Blue Regions

Chromosomes in green & Telomeres in yellow

• 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

Anchorage, cell density, and chemical growth factors affect cell

division

• Cells continue dividing until they touch one another

– This is called density-dependent inhibition

Cells anchor to dish surface and divide.

Figure 8.8A

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).

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

After forming a single layer, cells have stopped dividing.

Figure 8.8B

Providing an additional supply of growth factors stimulates further cell division.

See pg. 232

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

Tumor

Figure 8.10

Glandulartissue

1 2 3A tumor grows from a single cancer cell.

Cancer cells invade neighboring tissue.

Lymphvessels

Cancer cells spread through lymph and blood vessels to other parts of the body.

Metastasis

• 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

Growing out of control, cancer cells produce Malignant tumors

• Breast cancer cell

Figure 8.10x1

• Mammograms

Figure 8.10x2

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 forminghttp://www.ncl.ox.ac.uk/quicktime/taxol.html

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

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.

Cell Differentiationhttp://learn.genetics.utah.edu/units/stemcells/whatissc/

Evolution of Mitosis

Chromosomes attach to the plasma membrane

Chromosomes attach to the nuclear membrane

Pass through the nucleus

Spindle forms within the nucleus

Introductory Questions #31) Which phase is used to obtain pictures of chromosomes

in order to generate a karyotype2) 3) Give five differences between Mitosis and Meiosis.3) Name three factors in Meiosis & reproduction that

contributes in increasing genetic variability within a population.

4) What is a polar body? How is oogenesis different from spematogenesis?

5) How is a sporophyte different from a gametophyte? What do they produce and what process is involved, mitosis or meiosis?

6) What is a tetrad? Which phase of Meiosis does crossing over occur?

Heredity, Life Cycles, and Meiosis Chapter 13

HeredityHeredity: the transmission of traits

from one generation to the nextAsexual reproduction: clonesSexual reproduction: variationHuman 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

• The human life cycle

Figure 8.13

MEIOSIS FERTILIZATION

Haploid gametes (n = 23)

Egg cell

Sperm cell

Diploidzygote

(2n = 46)Multicellular

diploid adults (2n = 46)

Mitosis anddevelopment

Alternative Life CyclesFungi/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)

• Human female karyotype

Figure 8.19x2

• Human male karyotype

Figure 8.19x4

Meiosis• Chromosome replicate• 2 Cell divisions occur (Meiosis I & Meiosis II)• 4 daughter cells are

made all are (n): haploid• Homologous Chrom’s

separate in meiosis I• Meiosis II = Mitosis

(chromatids separate)

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

Homologous chromosomes carry different versions of genes

Homologous Chromosomes(Are they identical?)

Sister Chromatids

♂ from father from mother

Tetrad (Bivalent)

Figure 8.14, part 1

MEIOSIS I: Homologous chromosomes separate

INTERPHASE PROPHASE I METAPHASE I ANAPHASE I

Centrosomes(withcentriolepairs)

Nuclearenvelope

Chromatin

Sites of crossing over

Spindle

Sisterchromatids

Tetrad

Microtubules attached tokinetochore

Metaphaseplate

Centromere(with kinetochore)

Sister chromatidsremain attached

Homologouschromosomes separate

• Crossing over is the exchange of corresponding segments between two homologous chromosomes

• Genetic recombination results from crossing over during prophase I of meiosis

Crossing over further increases genetic variability

Figure 8.18A

TetradChaisma

Centromere

Synaptonemal Complex- Pg 213

• Protein that hold homologous chromosomes together

• Thought to be involved in crossing over events

• How crossing over leads to genetic recombination

Figure 8.18B

Tetrad(homologous pair ofchromosomes in synapsis)

Breakage of homologous chromatids

Joining of homologous chromatids

Chiasma

Separation of homologouschromosomes at anaphase I

Separation of chromatids atanaphase II and completion of meiosis

Parental type of chromosome

Recombinant chromosome

Recombinant chromosome

Parental type of chromosome

Gametes of four genetic types

1

2

3

4

Coat-colorgenes

Eye-colorgenes

Figure 8.17A, B

Coat-color genes Eye-color genes

Brown Black

C E

c e

White Pink

C E

c e

C E

c e

Tetrad in parent cell(homologous pair of

duplicated chromosomes)

Chromosomes ofthe four gametes

Origins of Genetic Variation

(1) Independent assortment: How they line up during metaphase I

Matters!!!

Homologous pairs of chromosomesposition and orient themselvesRandomly. (random positioning)

Different combinations are possible when gametes are produced.

Figure 8.16

POSSIBILITY 1 POSSIBILITY 2

Two equally probable

arrangements of chromosomes at

metaphase I

Metaphase II

Gametes

Combination 1 Combination 2 Combination 3 Combination 4

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!

Figure 8.14, part 2

MEIOSIS II: Sister chromatids separate

TELOPHASE IAND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II

Cleavagefurrow

Sister chromatidsseparate

TELOPHASE IIAND CYTOKINESIS

Haploiddaughter cellsforming

Meiosis vs. Mitosishttp://www.pbs.org/wgbh/nova/baby/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.

Figure 8.15

MITOSIS MEIOSIS

PARENT CELL(before chromosome replication)

Site ofcrossing over

MEIOSIS I

PROPHASE ITetrad formedby synapsis of homologous chromosomes

PROPHASE

Duplicatedchromosome(two sister chromatids)

METAPHASE

Chromosomereplication

Chromosomereplication

2n = 4

ANAPHASETELOPHASE

Chromosomes align at the metaphase plate

Tetradsalign at themetaphase plate

METAPHASE I

ANAPHASE ITELOPHASE I

Sister chromatidsseparate duringanaphase

Homologouschromosomesseparateduringanaphase I;sisterchromatids remain together

No further chromosomal replication; sister chromatids separate during anaphase II

2n 2n

Daughter cellsof mitosis

Daughter cells of meiosis II

MEIOSIS II

Daughtercells of

meiosis I

Haploidn = 2

n n n n

Introductory Questions #21) 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?

• Translocation

Figure 8.23Bx

• 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

• 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

• Human female bands

Figure 8.19x1

• Human female karyotype

Figure 8.19x2

• Human male bands

Figure 8.19x3

• Human male karyotype

Figure 8.19x4

• Down syndrome karyotype

Figure 8.20Ax

• Klinefelter’s karyotype

Figure 8.22Ax

• XYY karyotype

Figure 8.22x