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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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