Cellular ReproductionCellular Reproduction

Cell DivisionCell Division cellular material is divided between cellular material is divided between new daughter cells new daughter cells

Nuclear division: Mitosis or MeiosisNuclear division: Mitosis or Meiosis

Cytoplasmic division: CytokinesisCytoplasmic division: Cytokinesis

Mitosis and Meiosis in the Human Life CycleMitosis and Meiosis in the Human Life Cycle

2n = diploid = 2 sets of chromosomes2n = diploid = 2 sets of chromosomes n = haploid = 1 set of chromosomesn = haploid = 1 set of chromosomes

Cell Cycle with Mitosis Cell Cycle with Mitosis

G1S

G2

cytoplasm doubles

chromosomesreplicate

assembly of components for division cytokinesis

P MA

T

MitosisMitosisMitosis

P = prophaseP = prophase M = metaphaseM = metaphase

A = anaphaseA = anaphaseT = telophaseT = telophase

InterphaseInterphaseG1 = growth phase 1G1 = growth phase 1

S = synthesis phaseS = synthesis phaseG2 = growth phase 2G2 = growth phase 2

Interphase

Applying Your KnowledgeApplying Your Knowledge

A.A. When does nuclear division occur? When does nuclear division occur?

B.B. When are the chromosomes duplicated? When are the chromosomes duplicated?

C.C. When do the cytoplasmic contents When do the cytoplasmic contents double? double?

1.1. G1G12.2. SS3.3. G2G24.4. MitosisMitosis5.5. CytokinesisCytokinesis

Chromatin is diffuse, Chromatin is diffuse, individual chromosomes individual chromosomes cannot be distinguished.cannot be distinguished.

InterphaseInterphase

nucleus

nucleolus

Chromosomes condense.Chromosomes condense.Spindle forms.Spindle forms.Nucleolus disappears.Nucleolus disappears.Nuclear envelope breaks down.Nuclear envelope breaks down.

ProphaseProphase

Each chromosome appears as a pair of Each chromosome appears as a pair of chromatids attached at the centromere. chromatids attached at the centromere.

chromatid chromatid

centromere centromere

Sister Sister Chromatids are Chromatids are held together held together at their at their centromeres. centromeres.

chromatid chromatid

Chromatid pairs align Chromatid pairs align at the cell equator.at the cell equator.

MetaphaseMetaphase

Sister chromatids separate Sister chromatids separate

and are drawn to opposite and are drawn to opposite poles by spindle fibers.poles by spindle fibers.

AnaphaseAnaphase

Chromosomes have reached poles of cell. Chromosomes have reached poles of cell. Spindle disperses.Spindle disperses.Nuclear envelope surrounds chromosomes. Nuclear envelope surrounds chromosomes. Chromosomes become diffuse, nucleolus reforms.Chromosomes become diffuse, nucleolus reforms.

TelophaseTelophase

Telophase +Telophase +CytokinesisCytokinesis

These phases can overlap in time.These phases can overlap in time.

New Daughter CellsNew Daughter Cells

Cytokinesis in animal cellsCytokinesis in animal cells

Cytokinesis in plant cellsCytokinesis in plant cells

Applying Your KnowledgeApplying Your Knowledge

A.A. When do chromosomes line up at the When do chromosomes line up at the cell equator? cell equator?

B.B. When are sister chromatids first visible? When are sister chromatids first visible?

C.C. When do sister chromatids separate When do sister chromatids separate from each other? from each other?

1.1. ProphaseProphase2.2. MetaphaseMetaphase3.3. AnaphaseAnaphase4.4. TelophaseTelophase

Outcome of Meiotic DivisionsOutcome of Meiotic Divisions

Human Cell with Human Cell with 46 chromosomes46 chromosomes (Diploid) (Diploid)

4 Genetically-Different 4 Genetically-Different Human Cells , Each with Human Cells , Each with 23 chromosomes23 chromosomes (Haploid) (Haploid)

Duplication of Cell ContentsDuplication of Cell Contents

Two Chromosomal DivisionsTwo Chromosomal Divisions(Meiosis I and Meiosis II)(Meiosis I and Meiosis II)

Homologous Chromosome PairsHomologous Chromosome Pairs

• Diploid cells have Diploid cells have pairs of pairs of chromosomeschromosomes

• Each homologous Each homologous chromosome pair chromosome pair is genetically is genetically matched so that matched so that the genes are the genes are arranged in the arranged in the same order same order

Cell Cycle With Meiosis Cell Cycle With Meiosis

G1S

G2

cytoplasm doubles

chromosomesreplicate

assembly of components for division cytokinesis

M1

MeiosisMeiosisMeiosis

M1 = meiosis IM1 = meiosis I M2 = meiosis IIM2 = meiosis II

InterphaseInterphase

G1 = growth phase 1G1 = growth phase 1 S = synthesis phaseS = synthesis phaseG2 = growth phase 2G2 = growth phase 2

Interphase

M2

Applying Your KnowledgeApplying Your Knowledge

A.A. When does chromosome duplication When does chromosome duplication occur?occur?

B.B. When do the cytoplasmic contents double?When do the cytoplasmic contents double?

C.C. When does chromosomal division occur? When does chromosomal division occur?

1.1. G1 phaseG1 phase

2.2. S phase S phase

3.3. G2 phaseG2 phase

4.4. Meiosis I and IIMeiosis I and II

Meiotic DivisionsMeiotic Divisions

Meiosis I: reduction divisionMeiosis I: reduction division

Separation of homologous chromosomes Separation of homologous chromosomes into two different nucleiinto two different nucleiChromosome number reduced to haploidChromosome number reduced to haploid

Meiosis II: equational divisionMeiosis II: equational divisionDuplicated chromosomes separateDuplicated chromosomes separateNo change in chromosome numberNo change in chromosome number

Phases of Meiosis I Phases of Meiosis I

Prophase IProphase I --Chromosomes Shorten and --Chromosomes Shorten and Thicken (condense) Thicken (condense)--Homologous Chromosomes --Homologous Chromosomes Pair with Each Other and Pair with Each Other and Exchange Genetic Information Exchange Genetic Information

Metaphase IMetaphase I Chromosome Pairs Line up at Chromosome Pairs Line up at Cell EquatorCell Equator

Anaphase IAnaphase I Homologous Chromosomes Homologous Chromosomes SeparateSeparate

Telophase ITelophase I Separated Homologues Reach Separated Homologues Reach Opposite Poles Opposite Poles

Chromosomes condense.Chromosomes condense.Synapsis (pairing) of homologs occurs. Synapsis (pairing) of homologs occurs. Crossing-over occurs at chiasma (contact points).Crossing-over occurs at chiasma (contact points).

Non-sister Non-sister chromatidschromatids

ChromatidChromatid(duplicate)(duplicate)

CentromeresCentromeres

Crossing Crossing OverOver

HomologousHomologousPairs Pairs Exchange Exchange Genetic Genetic InformationInformation

ChromosomesChromosomeswith combinations with combinations of maternal and of maternal and paternal traitspaternal traits

Chromosome pairs align Chromosome pairs align at the center of the spindle. at the center of the spindle.

Homologues move to Homologues move to opposite poles of the cell. opposite poles of the cell.

I

Homologues reach Homologues reach opposite poles. opposite poles.

Prior to the start of Prior to the start of Meiosis II, there may be Meiosis II, there may be a pause called a pause called interkinesis but the interkinesis but the chromosomes do not chromosomes do not duplicate a second time. duplicate a second time.

Cytokinesis along the Cytokinesis along the central plane yields two central plane yields two haploid cells with haploid cells with duplicated duplicated chromosomes. chromosomes.

Phases of Meiosis II Phases of Meiosis II

Prophase IIProphase II --Chromosomes Shorten and --Chromosomes Shorten and Thicken (condense) Thicken (condense)

--No Chromosome Pairing Occurs--No Chromosome Pairing Occurs

Metaphase IIMetaphase II Chromosomes Line up at Cell Chromosomes Line up at Cell EquatorEquator

Anaphase IIAnaphase II Sister Chromatids SeparateSister Chromatids Separate

Telophase IITelophase II Separated Chromosomes Reach Separated Chromosomes Reach Opposite Poles Opposite Poles

Chromosomes Chromosomes condense.condense.

Chromosomes align Chromosomes align at the cell equators at the cell equators on the new spindles.on the new spindles.

Sister chromatids Sister chromatids

separate at separate at centromerescentromeresand move toand move toopposite poles. opposite poles.

Daughter chromosomes Daughter chromosomes reach opposite poles. reach opposite poles.

After cytokinesis, After cytokinesis, four genetically-different four genetically-different haploid cells are formed. haploid cells are formed.

Sperm formationSperm formation

•Equal divisions ofEqual divisions of cytoplasm cytoplasm•Four functional Four functional products per meiosis products per meiosis

Egg formationEgg formation

•Unequal divisions of Unequal divisions of cytoplasm cytoplasm•Small polar bodies formedSmall polar bodies formed•One functional product per One functional product per

meiosis meiosis

Applying Your KnowledgeApplying Your Knowledge

A.A. When do sister chromatids separate?When do sister chromatids separate?

B.B. When does crossing over occur?When does crossing over occur?

C.C. When do homologous pairs line up at When do homologous pairs line up at the cell equator?the cell equator?

1.1. Prophase IProphase I

2.2. Metaphase IMetaphase I

3.3. Anaphase IAnaphase I

4.4. Metaphase IIMetaphase II

5.5. Anaphase IIAnaphase II

Comparing Mitosis and MeiosisComparing Mitosis and Meiosis

MitosisMitosis MeiosisMeiosisCell type at start Cell type at start

Cell type at endCell type at end

Are products identical? (Y/N)Are products identical? (Y/N)

Number of cells producedNumber of cells produced

Number of chromosome Number of chromosome duplicationsduplications

Pairing of homologues (Y/N)Pairing of homologues (Y/N)

Crossing-over (Y/N)Crossing-over (Y/N)

Number of chromosome Number of chromosome divisionsdivisions

Comparing Mitosis and MeiosisComparing Mitosis and Meiosis

MitosisMitosis MeiosisMeiosisCell type at start Cell type at start DiploidDiploid DiploidDiploidCell type at endCell type at end DiploidDiploid HaploidHaploidAre products identical? (Y/N)Are products identical? (Y/N) YesYes NoNoNumber of cells producedNumber of cells produced TwoTwo FourFourNumber of chromosome Number of chromosome duplications prior toduplications prior to

OneOne OneOne

Pairing of homologues (Y/N)Pairing of homologues (Y/N) NoNo YesYesCrossing-over (Y/N)Crossing-over (Y/N) NoNo YesYesNumber of chromosome Number of chromosome divisionsdivisions

OneOne TwoTwo