1. Mitosis, Meiosis,Mitosis, Meiosis,
and Life Cyclesand Life Cycles
Chapter 12Chapter 12

2. LEARNING OBJECTIVE 1LEARNING OBJECTIVE 1
• Distinguish between aDistinguish between a haploid cellhaploid cell andand
aa diploid celldiploid cell
• DefineDefine homologous chromosomeshomologous chromosomes

3. KEY TERMSKEY TERMS
• DIPLOID (2DIPLOID (2NN))
•
The condition of having two sets ofThe 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 hochromosomes are present in pairs called ho
mologous pairsmologous pairs
• HAPLOID (HAPLOID (NN))
•
The condition of having one set ofThe condition of having one set of
chromosomes per nucleuschromosomes per nucleus

4. KEY TERMSKEY TERMS
• HOMOLOGOUS CHROMOSOMESHOMOLOGOUS CHROMOSOMES
•
Members of a chromosome pair that areMembers of a chromosome pair that are
similar in size, shape, and genetic constitutionsimilar in size, shape, and genetic constitution

6. LEARNING OBJECTIVE 2LEARNING OBJECTIVE 2
• Identify the phases in theIdentify the phases in the cell cyclecell cycle
• Describe the main events of eachDescribe the main events of each
phasephase

7. KEY TERMSKEY TERMS• CELL CYCLECELL CYCLE
•
Cyclic series of events in the life of a dividingCyclic series of events in the life of a dividing
eukaryotic celleukaryotic cell
•
The life of a cell from the time it is first formedThe life of a cell from the time it is first formed
from a dividing parent cell until its own divisionfrom a dividing parent cell until its own division
into two daughter cellsinto two daughter cells
•in unicellular organisms,in unicellular organisms,
division of one celldivision of one cell
reproduces the entirereproduces the entire
organismorganism

8. • functions in multicellular organismsfunctions in multicellular organisms
Cell DivisionCell Division

9. KEY TERMSKEY TERMS
• INTERPHASEINTERPHASE
•
Stage of the cell cycle between successiveStage of the cell cycle between successive
mitotic divisionsmitotic divisions

10. InterphaseInterphase
• During interphaseDuring interphase
•
Cells produces proteins, cell grows andCells produces proteins, cell grows and
prepares for next divisionprepares for next division
•
DNA replicatesDNA 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))

11. KEY TERMSKEY TERMS
• MITOSISMITOSIS
•
Division of the cell nucleus resulting in twoDivision of the cell nucleus resulting in two
daughter nuclei, each with the same numberdaughter nuclei, each with the same number
of chromosomes as the parent nucleusof chromosomes as the parent nucleus

12. KEY TERMSKEY TERMS
• CYTOKINESISCYTOKINESIS
•
Stage of cell division in which the cytoplasmStage of cell division in which the cytoplasm
divides to form two daughter cellsdivides to form two daughter cells

13. M PHASE
(Mitosis and cytokinesis)
S
(Synthesis phase)
G2
(Second gap
phase)
G1
(First gap phase)
Fig. 12-1, p. 242
G1- produce proteins
produce cyto-
plasmic organelles
S-synthesis of DNA
chromosomes are
duplicated
Makes more
proteins and
organelles and
completes preparation
for cell div.
G2

14. A Duplicated ChromosomeA Duplicated Chromosome

15. LEARNING OBJECTIVE 3LEARNING OBJECTIVE 3
• Describe the events that occur in eachDescribe the events that occur in each
stage ofstage of mitosismitosis

16. Stages of MitosisStages of Mitosis
• ProphaseProphase
• MetaphaseMetaphase
• AnaphaseAnaphase
• TelophaseTelophase

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

18. KEY TERMSKEY TERMS
• SPINDLESPINDLE
•
Structure consisting mainly ofStructure consisting mainly of microtubulesmicrotubules
that provides the framework for chromosomethat 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)

19. ProphaseProphase
• Chromatin condenses into chromosomesChromatin condenses into chromosomes
•
Nucleolus disappearsNucleolus disappears
•
Nuclear envelope breaks downNuclear envelope breaks down
•
MitoticMitotic spindlespindle begins to formbegins to form
• At the end of prophase, each duplicatedAt the end of prophase, each duplicated
chromosome is composed of two sisterchromosome is composed of two sister
chromatidschromatids

20. Microtubules
Sister
chromatids
Kinetochore
Centromere
region
Fig. 12-3, p. 245

21. MetaphaseMetaphase
• Duplicated chromosomes line up alongDuplicated chromosomes line up along
midplane of cellmidplane of cell

22. Interphase and MitosisInterphase and Mitosis

23. TelophaseTelophase
• Nuclear envelope forms around each setNuclear envelope forms around each set
of chromosomesof chromosomes
•
Nucleoli reappearNucleoli reappear
•
Chromosomes lengthen and becomeChromosomes lengthen and become
chromatinchromatin
•
Spindle disappearsSpindle disappears

24. AnaphaseAnaphase
• Sister chromatids separate and move toSister chromatids separate and move to
opposite poles of the cellopposite poles of the cell
•
Each chromatid is now a separateEach chromatid is now a separate
chromosomechromosome

25. KEY TERMSKEY TERMS
• CELL PLATECELL PLATE
•
Structure that forms duringStructure that forms during cytokinesiscytokinesis inin
plants, separating two daughter cellsplants, separating two daughter cells
produced by mitosisproduced by mitosis
• Cytokinesis generally takes place inCytokinesis generally takes place in
telophasetelophase

26. Plasma
membrane
Vesicles gather
on cell's
midplane
Small vesicles
fuse, forming
larger vesicles
Eventually one
large vesicle
exists
New cell walls
(from vesicle
contents)
New plasma
membranes
(from vesicle
membranes)
Cell plate
forming
Cell
wall
Cell plate
formingNucleus
Fig. 12-4, p. 247

27. (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
New
nuclei
Cell
plate
Fig. 12-2, p. 244

28. LEARNING OBJECTIVE 4LEARNING OBJECTIVE 4
• Explain whyExplain why meiosismeiosis is needed at someis needed at some
point in the life cycle of every sexuallypoint in the life cycle of every sexually
reproducing organismreproducing organism
• Describe the events that occur duringDescribe the events that occur during
meiosis Imeiosis I andand meiosis IImeiosis II

29. KEY TERMSKEY TERMS
• MEIOSISMEIOSIS
•
Process in which a 2Process in which a 2nn cell undergoescell undergoes
successive nuclear divisions, potentiallysuccessive nuclear divisions, potentially
producing fourproducing four nn nucleinuclei
•
Leads to formation of gametes andLeads to formation of gametes and sporesspores inin
plantsplants

30. MeiosisMeiosis
• preceded by the replication ofpreceded by the replication of
chromosomeschromosomes
• 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,
calledcalled meiosis Imeiosis I andand meiosis IImeiosis II
•Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

34. MeiosisMeiosis
• Meiosis must occur at some time in the lifeMeiosis must occur at some time in the life
of a sexually reproducing organism ifof a sexually reproducing organism if
gametesgametes are to be haploidare to be haploid
• Meiosis consists of two cell divisionsMeiosis consists of two cell divisions
•
Meiosis IMeiosis I
•
Meiosis IIMeiosis II

35. Meiosis IMeiosis I
• Members of each homologous pair ofMembers of each homologous pair of
chromosomes separate and arechromosomes separate and are
distributed into separate nuclei in twodistributed into separate nuclei in two
daughter cellsdaughter cells
•
Chromosomes were duplicated prior toChromosomes were duplicated prior to
meiosis I, so each consists of two chromatidsmeiosis I, so each consists of two chromatids

36. Meiosis IIMeiosis II
• Chromatids separate into individualChromatids separate into individual
chromosomes and are distributed intochromosomes and are distributed into
different haploid daughter cellsdifferent haploid daughter cells
•
Four haploid cells formFour haploid cells form

37. KEY TERMSKEY TERMS
• SYNAPSISSYNAPSIS
•
Physical association of homologousPhysical association of homologous
chromosomes during prophase I of meiosischromosomes during prophase I of meiosis

38. Crossing OverCrossing Over
• Crossing overCrossing over
•
Exchange of segments of homologousExchange of segments of homologous
chromosomeschromosomes
• SynapsisSynapsis andand crossing overcrossing over occuroccur
during prophase I of meiosisduring prophase I of meiosis

39. Crossing over
Sister
chromatids
Kinetochores
Fig. 12-6, p. 249

40. MeiosisMeiosis

41. MeiosisMeiosis

42. (a) Prophase I (d) Telophase I(c) Anaphase I(b) Metaphase I
Each
chromosome
consists of
two
chromatids
Homologous
chromosomes
Spindle
microtubules
New nuclei
Cell plate
Fig. 12-5 (a-d), p. 248

43. (e) Prophase II (h) Telophase II(g) Anaphase II(f) Metaphase II
Chromosomes
(each with two
chromatids)
Spindle
microtubules
New cell walls
and plasma
membranes
New
nuclei
Fig. 12-5 (e-h), p. 249

44. LEARNING OBJECTIVE 5LEARNING OBJECTIVE 5
• Compare and contrastCompare and contrast mitosismitosis andand
meiosismeiosis

45. MitosisMitosis
• Involves a single nuclear division in whichInvolves a single nuclear division in which
the two daughter cells formed arethe two daughter cells formed are
genetically identical to each other and togenetically identical to each other and to
the original cellthe original cell
• Synapsis of homologous chromosomesSynapsis of homologous chromosomes
does not occur during mitosisdoes not occur during mitosis

46. MeiosisMeiosis
• Involves two successive nuclear divisionsInvolves two successive nuclear divisions
and forms four haploid cells, each with aand forms four haploid cells, each with a
different combination of genesdifferent combination of genes
• Synapsis of homologous chromosomesSynapsis of homologous chromosomes
occurs during prophase I of meiosisoccurs during prophase I of meiosis

47. Mitosis and MeiosisMitosis and Meiosis

48. Two daughter cells (each 2n = 4)
identical to parent cell
Chromosomes
Prophase
Parent cell
(2n = 4)
Mitosis
Nuclear
envelope
Synapsis (pairing of
homologous chromosomes)
Prophase I
Prophase II
Parent cell
(2n = 4)
Nuclear
envelope1st
meiotic
division
2nd
meiotic
division
Four daughter cells (each n = 2)
genetically different from parent cell
Mitosis Meiosis
Fig. 12-7, p. 250

49. LEARNING OBJECTIVE 6LEARNING OBJECTIVE 6
• DefineDefine alternation of generationsalternation of generations

50. KEY TERMSKEY TERMS
• Alternation of generationsAlternation of generations
•
Plants alternate haploid and diploid generationsPlants alternate haploid and diploid generations
• SPOROPHYTESPOROPHYTE
•
22n,n, spore-producing stage in plant life cyclespore-producing stage in plant life cycle
• GAMETOPHYTEGAMETOPHYTE
•
n,n, gamete-producing stage in plant life cyclegamete-producing stage in plant life cycle

51. The SporophyteThe Sporophyte
• The 2The 2n,n, spore-producing stage in the lifespore-producing stage in the life
cycle of a plantcycle of a plant
• A diploid sporophyte plant forms haploidA diploid sporophyte plant forms haploid
spores by meiosisspores by meiosis
• A spore divides mitotically to form aA spore divides mitotically to form a
haploidhaploid gametophytegametophyte plantplant

52. The GametophyteThe Gametophyte
• TheThe n,n, gamete-producing stage in the lifegamete-producing stage in the life
cycle of a plantcycle of a plant
• The gametophyte produces haploidThe gametophyte produces haploid
gametes by mitosisgametes by mitosis
• Two gametes fuse to form a diploidTwo gametes fuse to form a diploid
zygotezygote, which divides mitotically to, which divides mitotically to
produce a diploidproduce a diploid sporophytesporophyte

53. 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

54. Animation: The Cell CycleAnimation: The Cell Cycle
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TO PLAY

55. Animation: ComparingAnimation: Comparing
Mitosis and MeiosisMitosis and Meiosis
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TO PLAY