Cell Division and Mitosis - PowerPoint PPT Presentation

1 / 65
About This Presentation
Title:

Cell Division and Mitosis

Description:

Parents produce a new generation of cells or multicelled ... anther. ovary. Chromosome Number. Sum total of chromosomes in a cell. Germ cells are diploid (2n) ... – PowerPoint PPT presentation

Number of Views:142
Avg rating:3.0/5.0
Slides: 66
Provided by: christin418
Category:

less

Transcript and Presenter's Notes

Title: Cell Division and Mitosis


1
Cell Division and Mitosis
  • Chapter 9

2
Understanding Cell Division
  • What instructions are necessary for inheritance?
  • How are those instructions duplicated for
    distribution into daughter cells?
  • By what mechanisms are instructions parceled out
    to daughter cells?

3
Reproduction
  • Parents produce a new generation of cells or
    multicelled individuals like themselves
  • Parents must provide daughter cells with
    hereditary instructions, encoded in DNA, and
    enough metabolic machinery to start up their own
    operation

4
Division Mechanisms
  • Eukaryotic organisms
  • Mitosis
  • Meiosis
  • Prokaryotic organisms
  • Prokaryotic fission

5
Roles of Mitosis
  • Multicelled organisms
  • Growth
  • Cell replacement
  • Some protistans, fungi, plants, animals
  • Asexual reproduction

6
Chromosome
  • A DNA molecule attached proteins
  • Duplicated in preparation for mitosis

one chromosome (unduplicated)
one chromosome (duplicated)
7
Chromosome Number
  • Sum total of chromosomes in a cell
  • Somatic cells
  • Chromosome number is diploid (2n)
  • Two of each type of chromosome
  • Gametes
  • Chromosome number is haploid (n)
  • One of each chromosome type

8
Human Chromosome Number
  • Diploid chromosome number (n) 46
  • Two sets of 23 chromosomes each
  • One set from father
  • One set from mother
  • Mitosis produces cells with 46 chromosomes--two
    of each type

9
Organization of Chromosomes
DNA
one nucleosome
DNA and proteins arranged as cylindrical fiber
histone
10
The Cell Cycle
interphase
G1
S
telophase
anaphase
Mitosis
G2
metaphase
prophase
11
Interphase
  • Usually longest part of the cycle
  • Cell increases in mass
  • Number of cytoplasmic components doubles
  • DNA is duplicated

12
Mitosis
  • Period of nuclear division
  • Usually followed by cytoplasmic division
  • Four stages
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

13
Control of the Cycle
  • Once S begins, the cycle automatically runs
    through G2 and mitosis
  • The cycle has a built-in molecular brake in G1
  • Cancer involves a loss of control over the cycle,
    malfunction of the brakes

14
Stopping the Cycle
  • Some cells normally stop in interphase
  • Neurons in human brain
  • Arrested cells do not divide
  • Adverse conditions can stop cycle
  • Nutrient-deprived amoebas get stuck in interphase

15
The Spindle Apparatus
  • Consists of two distinct sets of microtubules
  • Each set extends from one of the cell poles
  • Two sets overlap at spindle equator
  • Moves chromosomes during mitosis

16
Spindle Apparatus
one spindle pole
one of the condensed chromosomes
spindle equator
microtubules organized as a spindle apparatus
one spindle pole
17
Maintaining Chromosome Number

18
Stages of Mitosis
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

19
Early Prophase - Mitosis Begins
  • Duplicated chromosomes begin to condense

20
Late Prophase
  • New microtubules are assembled
  • One centriole pair is moved toward opposite pole
    of spindle
  • Nuclear envelope starts to break up

21
Transition to Metaphase
  • Spindle forms
  • Spindle microtubules become attached to the two
    sister chromatids of each chromosome

22
Metaphase
  • All chromosomes are lined up at the spindle
    equator
  • Chromosomes are maximally condensed

23
Anaphase
  • Sister chromatids of each chromosome are pulled
    apart
  • Once separated, each chromatid is a chromosome

24
Telophase
  • Chromosomes decondense
  • Two nuclear membranes form, one around each set
    of unduplicated chromosomes

25
Results of Mitosis
  • Two daughter nuclei
  • Each with same chromosome number as parent cell
  • Chromosomes in unduplicated form

26
Cytoplasmic Division
  • Usually occurs between late anaphase and end of
    telophase
  • Two mechanisms
  • Cell plate formation (plants)
  • Cleavage (animals)

27
Cell Plate Formation
28
Animal Cell Division
29
HeLa Cells
  • Line of human cancer cells that can be grown in
    culture
  • Descendents of tumor cells from a woman named
    Henrietta Lacks
  • Lacks died at 31, but her cells continue to live
    and divide in labs around the world

30
Meiosis
  • Chapter 10

31
Sexual Reproduction
  • Chromosomes are duplicated in germ cells
  • Germ cells undergo meiosis and cytoplasmic
    division
  • Cellular descendents of germ cells become gametes
  • Gametes meet at fertilization

32
Asexual Reproduction
  • Single parent produces offspring
  • All offspring are genetically identical to one
    another and to parent

33
Sexual Reproduction
  • Involves
  • Meiosis
  • Gamete production
  • Fertilization
  • Produces genetic variation among offspring

34
Homologous Chromosomes Carry Different Alleles
  • Cell has two of each chromosome
  • One chromosome in each pair from mother, other
    from father
  • Paternal and maternal chromosomes carry different
    alleles

35
Sexual Reproduction Shuffles Alleles
  • Through sexual reproduction, offspring inherit
    new combinations of alleles, which leads to
    variations in traits
  • This variation in traits is the basis for
    evolutionary change

36
Gamete Formation
  • Gametes are sex cells (sperm, eggs)
  • Arise from germ cells

ovaries
anther
ovary
testes
37
Chromosome Number
  • Sum total of chromosomes in a cell
  • Germ cells are diploid (2n)
  • Gametes are haploid (n)
  • Meiosis halves chromosome number

38
Meiosis Two Divisions
  • Two consecutive nuclear divisions
  • Meiosis I
  • Meiosis II
  • DNA is not duplicated between divisions
  • Four haploid nuclei form

39
Meiosis I
Each homologue in the cell pairs with its
partner,
then the partners separate
40
Meiosis II
  • The two sister chromatids of each duplicated
    chromosome are separated from each other

two chromosomes (unduplicated)
one chromosome (duplicated)
41
Meiosis I - Stages
42
Prophase I
  • Each duplicated chromosome pairs with homologue
  • Homologues swap segments
  • Each chromosome becomes attached to spindle

43
Metaphase I
  • Chromosomes are pushed and pulled into the middle
    of cell
  • The spindle is fully formed

44
Anaphase I
  • Homologous chromosomes segregate
  • The sister chromatids remain attached

45
Telophase I
  • The chromosomes arrive at opposite poles
  • Usually followed by cytoplasmic division

46
Prophase II
  • Microtubules attach to the kinetochores of the
    duplicated chromosomes

47
Metaphase II
  • Duplicated chromosomes line up at the spindle
    equator, midway between the poles

48
Anaphase II
  • Sister chromatids separate to become independent
    chromosomes

49
Telophase II
  • The chromosomes arrive at opposite ends of the
    cell
  • A nuclear envelope forms around each set of
    chromosomes
  • Four haploid cells

50
Crossing Over
  • Each chromosome becomes zippered to its homologue
  • All four chromatids are closely aligned
  • Nonsister chromosomes exchange segments

51
Effect of Crossing Over
  • After crossing over, each chromosome contains
    both maternal and paternal segments
  • Creates new allele combinations in offspring

52
Random Alignment
  • During transition between prophase I and
    metaphase I, microtubules from spindle poles
    attach to kinetochores of chromosomes
  • Initial contacts between microtubules and
    chromosomes are random

53
Random Alignment
  • Either the maternal or paternal member of a
    homologous pair can end up at either pole
  • The chromosomes in a gamete are a mix of
    chromosomes from the two parents

54
Possible Chromosome Combinations
  • As a result of random alignment, the number of
    possible combinations of chromosomes in a gamete
    is
  • 2n
  • (n is number of chromosome types)

55
Possible ChromosomeCombinations
1
2
3
or
or
or
56
Plant Life Cycle
multicelled sporophyte
mitosis
zygote
Diploid
meiosis
fertilization
Haploid
spores
gametes
multicelled gametophytes
mitosis
57
Animal Life Cycle
multicelled body
mitosis
zygote
Diploid
meiosis
fertilization
Haploid
gametes
58
Oogenesis
three polar bodies (haploid)
first polar body (haploid)
primary oocyte (diploid)
oogonium (diploid)
secondary oocyte (haploid)
ovum (haploid)
Meiosis I, Cytoplasmic Division
Meiosis II, Cytoplasmic Division
Growth
59
Spermatogenesis
primary spermatocyte (diploid)
spermato-gonium (diploid )
sperm (mature, haploid male gametes)
secondary spermatocytes (haploid)
spermatids (haploid)
Meiosis I, Cytoplasmic Division
Meiosis II, Cytoplasmic Division
Growth
cell differentiation, sperm formation
60
Fertilization
  • Male and female gametes unite and nuclei fuse
  • Fusion of two haploid nuclei produces diploid
    nucleus in the zygote
  • Which two gametes unite is random
  • Adds to variation among offspring

61
Factors Contributing to Variation among Offspring
  • Crossing over during prophase I
  • Random alignment of chromosomes at metaphase I
  • Random combination of gametes at fertilization

62
Mitosis Meiosis Compared
  • Mitosis
  • Functions
  • Asexual reproduction
  • Growth, repair
  • Occurs in somatic cells
  • Produces clones
  • Meiosis
  • Function
  • Sexual reproduction
  • Occurs in germ cells
  • Produces variable offspring

63
Prophase vs. Prophase I
  • Prophase (Mitosis)
  • Homologous pairs do not interact with each other
  • Prophase I (Meiosis)
  • Homologous pairs become zippered together and
    crossing over occurs

64
Anaphase, Anaphase I, and Anaphase II
  • Anaphase I (Meiosis)
  • Homologous chromosomes separate from each other
  • Anaphase/Anaphase II (Mitosis/Meiosis)
  • Sister chromatids of a chromosome separate from
    each other

65
Results of Mitosis and Meiosis
  • Mitosis
  • Two diploid cells produced
  • Each identical to parent
  • Meiosis
  • Four haploid cells produced
  • Differ from parent and one another
Write a Comment
User Comments (0)
About PowerShow.com