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

Chapter 12Chapter 12

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 pairschromosomes are present in 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

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 celleukaryotic cell

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 • cell grows and prepares for next divisioncell grows and prepares 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

Cell CycleCell Cycle

Stages of Mitosis Stages of Mitosis

• ProphaseProphase • MetaphaseMetaphase• AnaphaseAnaphase• TelophaseTelophase

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

A Duplicated ChromosomeA Duplicated Chromosome

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

MetaphaseMetaphase

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

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

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

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

CytokinesisCytokinesis

Interphase and MitosisInterphase and Mitosis

(a) Interphase (b) Prophase

Condensing chromosome(consists of 2 sister chromatids)

(d) Anaphase

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

(e) Telophase

Newnuclei

Cell plate

Fig. 12-2, p. 244

(c) Metaphase

Spindle microtubules

Stepped Art

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 Leads to formation of sporesspores in plants in plants

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 OverCrossing Over

MeiosisMeiosis

MeiosisMeiosis

LEARNING OBJECTIVE LEARNING OBJECTIVE

• 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

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

Plant Life CyclePlant Life Cycle