Mitosis, Meiosis, Mitosis, Meiosis, and Life Cyclesand Life Cycles

Chapter 12Chapter 12

LEARNING OBJECTIVE 1LEARNING OBJECTIVE 1

• Distinguish between a Distinguish between a haploid cellhaploid cell and and a a diploid celldiploid cell

• Define Define homologous chromosomeshomologous chromosomes

KEY TERMSKEY TERMS

• DIPLOID (2DIPLOID (2NN)) • The condition of having two sets of The condition of having two sets of

chromosomes per nucleuschromosomes per nucleus • In somatic cells of dIn somatic cells of diploid organisms,iploid organisms,

chromosomes are present in pairs called ho chromosomes are present in pairs called ho mologous pairsmologous pairs

• HAPLOID (HAPLOID (NN)) • The condition of having one set of The condition of having one set of

chromosomes per nucleuschromosomes per nucleus

KEY TERMSKEY TERMS

• HOMOLOGOUS CHROMOSOMESHOMOLOGOUS CHROMOSOMES • Members of a chromosome pair that are Members of a chromosome pair that are

similar in size, shape, and genetic constitutionsimilar in size, shape, and genetic constitution

LEARNING OBJECTIVE 2LEARNING OBJECTIVE 2

• Identify the phases in the Identify the phases in the cell cyclecell cycle

• Describe the main events of each Describe the main events of each phasephase

KEY TERMSKEY TERMS• CELL CYCLECELL CYCLE • Cyclic series of events in the life of a dividing Cyclic series of events in the life of a dividing

eukaryotic cell eukaryotic cell • The life of a cell from the time it is first formed The life of a cell from the time it is first formed

from a dividing parent cell until its own division from a dividing parent cell until its own division into two daughter cellsinto two daughter cells

•in unicellular organisms, in unicellular organisms, division of one cell division of one cell reproduces the entire reproduces the entire organismorganism

• functions in multicellular organismsfunctions in multicellular organisms

Cell DivisionCell Division

KEY TERMSKEY TERMS

• INTERPHASEINTERPHASE • Stage of the cell cycle between successive Stage of the cell cycle between successive

mitotic divisionsmitotic divisions

InterphaseInterphase• During interphase During interphase

• Cells produces proteins, cell grows and Cells produces proteins, cell grows and prepares for next divisionprepares for next division

• DNA replicates DNA replicates

• Interphase is divided intoInterphase is divided into• first gap phase (Gfirst gap phase (G11))• synthesis phase (S)synthesis phase (S)• second gap phase (Gsecond gap phase (G22) )

KEY TERMSKEY TERMS

• MITOSIS MITOSIS • Division of the cell nucleus resulting in two Division of the cell nucleus resulting in two

daughter nuclei, each with the same number daughter nuclei, each with the same number of chromosomes as the parent nucleusof chromosomes as the parent nucleus

KEY TERMSKEY TERMS

• CYTOKINESISCYTOKINESIS • Stage of cell division in which the cytoplasm Stage of cell division in which the cytoplasm

divides to form two daughter cellsdivides to form two daughter cells

M PHASE(Mitosis and cytokinesis)

S(Synthesis phase)

G2

(Second gapphase)

G1

(First gap phase)

Fig. 12-1, p. 242

G1- produce proteins produce cyto- plasmic organelles

S-synthesis of DNA chromosomes are duplicated

Makes moreproteins and organelles andcompletes preparationsfor cell div.

G2

A Duplicated ChromosomeA Duplicated Chromosome

LEARNING OBJECTIVE 3LEARNING OBJECTIVE 3

• Describe the events that occur in each Describe the events that occur in each stage of stage of mitosismitosis

Stages of Mitosis Stages of Mitosis

• ProphaseProphase • MetaphaseMetaphase• AnaphaseAnaphase• TelophaseTelophase

•Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

KEY TERMSKEY TERMS

• SPINDLESPINDLE • Structure consisting mainly of Structure consisting mainly of microtubulesmicrotubules

that provides the framework for chromosome that provides the framework for chromosome movement during cell divisionmovement during cell division

• Begins to form in cytoplasm during ProphaseBegins to form in cytoplasm during Prophase

at the centrosome (microtubule-organizing center)at the centrosome (microtubule-organizing center)

ProphaseProphase

• Chromatin condenses into chromosomesChromatin condenses into chromosomes• Nucleolus disappears Nucleolus disappears • Nuclear envelope breaks downNuclear envelope breaks down• Mitotic Mitotic spindlespindle begins to form begins to form

• At the end of prophase, each duplicated At the end of prophase, each duplicated chromosome is composed of two sister chromosome is composed of two sister chromatidschromatids

Microtubules

Sisterchromatids

Kinetochore

Centromereregion

Fig. 12-3, p. 245

MetaphaseMetaphase

• Duplicated chromosomes line up along Duplicated chromosomes line up along midplane of cellmidplane of cell

Interphase and MitosisInterphase and Mitosis

TelophaseTelophase

• Nuclear envelope forms around each set Nuclear envelope forms around each set of chromosomes of chromosomes

• Nucleoli reappear Nucleoli reappear • Chromosomes lengthen and become Chromosomes lengthen and become

chromatinchromatin• Spindle disappears Spindle disappears

AnaphaseAnaphase

• Sister chromatids separate and move to Sister chromatids separate and move to opposite poles of the cell opposite poles of the cell

• Each chromatid is now a separate Each chromatid is now a separate chromosome chromosome

KEY TERMSKEY TERMS

• CELL PLATECELL PLATE • Structure that forms during Structure that forms during cytokinesiscytokinesis in in

plants, separating two daughter cells plants, separating two daughter cells produced by mitosisproduced by mitosis

• Cytokinesis generally takes place in Cytokinesis generally takes place in telophasetelophase

Plasmamembrane

Vesicles gatheron cell'smidplane

Small vesiclesfuse, forming

larger vesicles

Eventually onelarge vesicle

exists

New cell walls(from vesicle

contents)

New plasmamembranes

(from vesiclemembranes)

Cell plateforming

Cellwall

Cell plateformingNucleus

Fig. 12-4, p. 247

(e) Telophase(a) Interphase (b) Prophase (c) Metaphase (d) Anaphase

Condensing chromosome(consists of 2 sister chromatids)

Spindle microtubules

Sister chromatids (now called chromosomes) move to opposite ends of cell

Newnuclei

Cell plate

Fig. 12-2, p. 244

LEARNING OBJECTIVE 4LEARNING OBJECTIVE 4

• Explain why Explain why meiosismeiosis is needed at some is needed at some point in the life cycle of every sexually point in the life cycle of every sexually reproducing organism reproducing organism

• Describe the events that occur during Describe the events that occur during meiosis Imeiosis I and and meiosis IImeiosis II

KEY TERMSKEY TERMS

• MEIOSISMEIOSIS • Process in which a 2Process in which a 2nn cell undergoes cell undergoes

successive nuclear divisions, potentially successive nuclear divisions, potentially producing four producing four nn nuclei nuclei

• Leads to formation of gametes and Leads to formation of gametes and sporesspores in in plantsplants

MeiosisMeiosis• preceded by the replication of chromosomespreceded by the replication of chromosomes• reduces the number of chromosome setsreduces the number of chromosome sets• takes place in two sets of cell divisions, takes place in two sets of cell divisions,

called called meiosis I meiosis I and and meiosis IImeiosis II

•Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

MeiosisMeiosis

• Meiosis must occur at some time in the life Meiosis must occur at some time in the life of a sexually reproducing organism if of a sexually reproducing organism if gametesgametes are to be haploid are to be haploid

• Meiosis consists of two cell divisionsMeiosis consists of two cell divisions• Meiosis I Meiosis I • Meiosis IIMeiosis II

Meiosis IMeiosis I

• Members of each homologous pair of Members of each homologous pair of chromosomes separate and are chromosomes separate and are distributed into separate nuclei in two distributed into separate nuclei in two daughter cells daughter cells

• Chromosomes were duplicated prior to Chromosomes were duplicated prior to meiosis I, so each consists of two chromatidsmeiosis I, so each consists of two chromatids

Meiosis IIMeiosis II

• Chromatids separate into individual Chromatids separate into individual chromosomes and are distributed into chromosomes and are distributed into different haploid daughter cells different haploid daughter cells

• Four haploid cells form Four haploid cells form

KEY TERMSKEY TERMS

• SYNAPSISSYNAPSIS • Physical association of homologous Physical association of homologous

chromosomes during prophase I of meiosischromosomes during prophase I of meiosis

Crossing OverCrossing Over

• Crossing overCrossing over • Exchange of segments of homologous Exchange of segments of homologous

chromosomes chromosomes

• Synapsis Synapsis andand crossing over crossing over occur during occur during prophase I of meiosisprophase I of meiosis

Crossing overSister

chromatids

Kinetochores

Fig. 12-6, p. 249

MeiosisMeiosis

MeiosisMeiosis

(a) Prophase I (d) Telophase I(c) Anaphase I(b) Metaphase I

Each chromosomeconsists of two chromatids

Homologouschromosomes

Spindlemicrotubules

New nuclei

Cell plate

Fig. 12-5 (a-d), p. 248

(e) Prophase II (h) Telophase II(g) Anaphase II(f) Metaphase II

Chromosomes(each with twochromatids)

Spindlemicrotubules

New cell wallsand plasmamembranes

New nuclei

Fig. 12-5 (e-h), p. 249

LEARNING OBJECTIVE 5LEARNING OBJECTIVE 5

• Compare and contrast Compare and contrast mitosismitosis and and meiosismeiosis

MitosisMitosis

• Involves a single nuclear division in which Involves a single nuclear division in which the two daughter cells formed are the two daughter cells formed are genetically identical to each other and to genetically identical to each other and to the original cellthe original cell

• Synapsis of homologous chromosomes Synapsis of homologous chromosomes does not occur during mitosisdoes not occur during mitosis

MeiosisMeiosis

• Involves two successive nuclear divisions Involves two successive nuclear divisions and forms four haploid cells, each with a and forms four haploid cells, each with a different combination of genes different combination of genes

• Synapsis of homologous chromosomes Synapsis of homologous chromosomes occurs during prophase I of meiosisoccurs during prophase I of meiosis

Mitosis and MeiosisMitosis and Meiosis

Two daughter cells (each 2n = 4)identical to parent cell

Chromosomes

Prophase

Parent cell(2n = 4)

Mitosis

Nuclearenvelope

Synapsis (pairing ofhomologous chromosomes)

Prophase I

Prophase II

Parent cell(2n = 4)

Nuclearenvelope1st

meioticdivision

2ndmeioticdivision

Four daughter cells (each n = 2)genetically different from parent cell

Mitosis MeiosisFig. 12-7, p. 250

LEARNING OBJECTIVE 6LEARNING OBJECTIVE 6

• Define Define alternation of generationsalternation of generations

KEY TERMSKEY TERMS

• Alternation of generationsAlternation of generations• Plants alternate haploid and diploid generationsPlants alternate haploid and diploid generations

• SPOROPHYTE SPOROPHYTE • 22n,n, spore-producing stage in plant life cycle spore-producing stage in plant life cycle

• GAMETOPHYTEGAMETOPHYTE • n,n, gamete-producing stage in plant life cycle gamete-producing stage in plant life cycle

The SporophyteThe Sporophyte

• The 2The 2n, n, spore-producing stage in the life spore-producing stage in the life cycle of a plant cycle of a plant

• A diploid sporophyte plant forms haploid A diploid sporophyte plant forms haploid spores by meiosis spores by meiosis

• A spore divides mitotically to form a A spore divides mitotically to form a haploid haploid gametophytegametophyte plant plant

The GametophyteThe Gametophyte

• The The n, n, gamete-producing stage in the life gamete-producing stage in the life cycle of a plantcycle of a plant

• The gametophyte produces haploid The gametophyte produces haploid gametes by mitosis gametes by mitosis

• Two gametes fuse to form a diploid Two gametes fuse to form a diploid zygotezygote, which divides mitotically to , which divides mitotically to produce a diploid produce a diploid sporophytesporophyte

Mitosis

Gametophyte (n)(multicellular

haploid organism)

Sporophyte (2n)(multicellular

diploid organism)

Spores (n)

Fertilization

Mitosis

Gametes (n)

Zygote (2n)

Mitosis

Meiosis

Fig. 12-8, p. 251

Animation: The Cell CycleAnimation: The Cell Cycle

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Animation: Comparing Animation: Comparing Mitosis and MeiosisMitosis and Meiosis

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