CH 8

Reproduction and Inheritance

Reproduction• Asexual Reproduction• Sexual Reproduction

LM 3

40

Prokaryoticchromosome

Plasmamembrane

Cell wall

Duplication of chromosomeand separation of copies

1

Continued elongation of thecell and movement of copies2

Division intotwo daughter cells

3

Prokaryotes are asexual• Via binary fission

– Recall that Prokaryotes have circular DNA

Figure 8.3A

Prokaryotic chromosomes

Eukaryotes

• Complex cell division

• Chromosomes occur as chromatin unless dividing

• Individual chromosomes visible when cell is dividing

LM 6

00

Cell cycle

• Ordered sequence of events from time a cell is first formed until its own division

• Growth phase• Division phase (mitotic phase)

– Mitosis – Cytokinesis

Fig. 8-5

S(DNA synthesis)G1

G2

Cytokinesis

Mito

sis

INTERPHASE

MITOTICPHASE (M)

Fig. 8-6a

Centrosomes(with centriole pairs) Kinetochore

Early mitoticspindle

Chromatin

INTERPHASE PROMETAPHASEPROPHASE

Centrosome Fragmentsof nuclearenvelope

Plasmamembrane

Chromosome, consistingof two sister chromatids

Nuclearenvelope

Spindlemicrotubules

Nucleolus

Centromere

Fig. 8-6b

Metaphaseplate

Nucleolusforming

METAPHASE TELOPHASE AND CYTOKINESISANAPHASE

Cleavagefurrow

Daughterchromosomes

NuclearenvelopeformingSpindle

Cytokenesis

Cleavagefurrow

Cleavage furrow Contracting ring ofmicrofilaments

Daughter cells

•Cleavage furrow

•Microfilaments contract

Cell plate Daughter cells

Cell wall

Vesicles containingcell wall material

Daughter nucleus

Cell plateformingWall of

parent cell

New cell wall

Plant cells

Cell plate

Cell Division

• Growth factors• Density-Dependent inhibition• Anchorage dependence

G1 checkpoint

Controlsystem

M

S

G2

G1

M checkpoint

G2 checkpoint

G0

Cell cycle control system

Set of molecules that triggers and coordinates key events in cell cycle

Growth

Fig. 8-9b

G1 checkpoint

Controlsystem

M

S

G2

G1

Receptorprotein

Signaltransductionpathway

Relayproteins

Plasma membrane

Growth factor

Out of control

• Cancer– Do not respond to cell control system– No density-dependent inhibition– Divide indefinitely

Meiosis terms

• Somatic cells• Homologous chromosomes• Sex chromosomes• Autosomes• Diploid• Haploid

Fig. 8-13

Haploid gametes (n = 23)

nnEgg cell

Sperm cellFertilizationMeiosis

Multicellulardiploid adults

(2n = 46)

Mitosis anddevelopment

nn

22nn

Diploidzygote

(2n = 46)

Meiosis

• Produces haploid gametes in diploid organisms

• Duplication of chromosomes– Two cell divisions

Fig. 8-14a

Centrosomes(with centriolepairs)

PROPHASE I

Microtubulesattached tokinetochore

INTERPHASE

Sites of crossing over Metaphaseplate

Spindle

MEIOSIS I: Homologous chromosomes separate

METAPHASE I

Sister chromatidsremain attached

ANAPHASE I

Nuclearenvelope

Sisterchromatids

Centromere(with kinetochore)

Homologouschromosomes separateChromatin

Tetrad

Fig. 8-14b

PROPHASE I

MEIOSIS II: Sister chromatids separate

METAPHASE II ANAPHASE II

Cleavagefurrow

TELOPHASE IIAND CYTOKINESIS

Sister chromatidsseparate

Haploid daughtercells forming

TELOPHASE IIAND CYTOKINESIS

Fig. 8-15

Prophase

Metaphase IMetaphase

2n = 4

Tetradsalign at themetaphase plate

Duplicatedchromosome(two sisterchromatids)

Parent cell(before chromosome duplication)

Chromosomeduplication

Chromosomesalign at themetaphase plate

AnaphaseTelophase Sister chromatids

separate duringanaphase

Daughter cellsof mitosis

2n 2n

n

Chromosomeduplication

Site ofcrossing over

Tetrad formedby synapsis ofhomologouschromosomes

MEIOSIS

Prophase I

Anaphase ITelophase I

MITOSIS

MEIOSIS I

Haploidn = 2

Daughtercells of

meiosis I

MEIOSIS II

n n n

Daughter cells of meiosis II

Homologouschromosomesseparate(anaphase I);sister chroma-tids remaintogether

No furtherchromosomalduplication;sisterchromatidsseparate(anaphase II)

Diversity

• Random arrangement of homologous chromosomes

• Different gene versions• Genetic recombination

– “Crossing over”

Nondisjunctionin meiosis I

Normalmeiosis II

n + 1

Gametes

Number of chromosomes

n + 1 n – 1 n – 1

Error

•Abnormal sex chromosomes

•Trisomy 21

Error

• Down syndrome– Extra copy of

chromosome 21