PowerLecture:%20Chapter%2019

1
PowerLectureChapter 19

• Cell Reproduction

2
Learning Objectives

• Understand the factors that cause cells to
  reproduce.
• Be able to describe a chromosome and tell the
  numbers found in sex and non-sex cells.
• Understand the cell cycle and be able to
  visualize where mitosis fits into the cell cycle.
• Be able to describe each phase of mitosis.
• Explain how the cytoplasm is apportioned to the
  daughter cells following mitosis.

3
Learning Objectives (contd)

• Understand the effect that meiosis has on
  chromosome number.
• Describe the events that occur in each meiotic
  phase.
• Compare mitosis and meiosis cite similarities
  and differences.

4
Impacts/Issues

• Henriettas
• Immortal Cells

5
Henriettas Immortal Cells

• Researchers at Johns Hopkins cultured a line of
  immortal cells in 1951.
• They are referred to as HeLa cells after their
  sourcea woman named Henrietta Lacks.
• Her cells continue to provide for research around
  the world.

6
Henriettas Immortal Cells

• Understanding cell division starts with three
  questions
• What kind of information guides inheritance?
• How is the information copied in a parent cell
  before being distributed into daughter cells?
• What mechanisms actually parcel out the
  information to daughter cells?

7
Video Producing Human Replacement Cells

• This video clip is available in CNN Today Videos
  for Genetics, 2005, Volume VII. Instructors,
  contact your local sales representative to order
  this volume, while supplies last.

8
Useful References for Impacts/Issues

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Disease Model Uses 3-D Cancer Cells
  Grown in Space. Cancer Weekly, Aug. 21, 2001.
• InfoTrac Stem Cells That Kill. Alice Park. Time,
  April 24, 2006.

9
How Would You Vote?

• To conduct an instant in-class survey using a
  classroom response system, access JoinIn Clicker
  Content from the PowerLecture main menu.
• Descendants of HeLa cells are sold all over the
  world by cell culture firms. Should the family of
  Henrietta Lacks share in the profits?
• a. Yes, many people have profited from Henrietta
  Lacks' cells her survivors should share in that.
• b. No, buying and selling genetic material is
  wrong.

10
Useful References for How Would You Vote?

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Companies Covet Genes Ethics and
  Profits Compete in the Patenting of Human Genetic
  Materials. Alternatives Journal, Summer 1997.
• Washington Post Life Itself Exploring the Realm
  of the Living Cell

11
Section 1

• Dividing Cells
• Bridge Generations

12
Dividing Cells Bridge Generations

• Division of the parent nucleus sorts DNA into
  nuclei for daughter cells.
• Reproduction, a part of the life cycle of living
  things, begins with the division of single cells.
• Each new generation must receive a duplicate of
  the parent cells DNA and enough cytoplasmic
  machinery to start up its own operation.
• DNA contains the genetic instructions for all of
  the
• proteins the cell makes.
• The cytoplasm contains the enzymes, organelles,
  and chemicals necessary for life.

13
Dividing Cells Bridge Generations

• The nuclei of eukaryotic cells divide by one of
  two mechanismsmitosis or meiosis.
• Mitosis occurs
• in somatic cells.
• Meiosis occurs
• only in germ cells
• that divide to
• form gametes.

14
Dividing Cells Bridge Generations

• Chromosomes are DNA packages in the cell
  nucleus.
• Chromosomes are molecules of DNA genes are
  segments of DNA on each chromosome.
• Chromosomes form complexes with protein in the
  nucleus to create chromatin.

15
Dividing Cells Bridge Generations

• Having two sets of chromosomes makes a cell
  diploid.
• The sum of the chromosomes in a cell of a given
  type is the chromosome number.
• All somatic cells have two copies of each
  chromosome, one from each parent, for a total of
  46 in humans somatic cells are diploid (2n) and
  they divide by mitosis.
• Of the 23 pairs of chromosomes in a somatic cell,
  pairs 1 through 22 are called autosomes
  autosomes are the same in length, shape, and
  traits.

16
Dividing Cells Bridge Generations

• Pair number 23 consists of the sex chromosomes
  the two types of chromosomes are X and Y (females
  are XX, males are XY).
• Paired corresponding chromosomes are homologous
  chromosomes (homologues).

Figure 19.1
17
Fig. 19.2, p. 355
mitosis, division of cytoplasm
a Two of the chromosomes (unduplicated) in a
parent cell at interphase
b The same two chromosomes, now duplicated, in
that cell at interphase, prior to mitosis
c Two chromosomes (unduplicated) in the parent
cells daughter cells, which both start life in
interphase.
18
Fig. 19.2, p. 355
mitosis, division of cytoplasm
a Two of the chromosomes (unduplicated) in a
parent cell at interphase
b The same two chromosomes, now duplicated, in
that cell at interphase, prior to mitosis
c Two chromosomes (unduplicated) in the parent
cells daughter cells, which both start life in
interphase.
Stepped Art
19
Dividing Cells Bridge Generations

• Having just one set of chromosomes makes a cell
  haploid.
• Spermatogonia and oogonia are diploid germ cells
  that give rise to haploid gametes (sperm and
  eggs, respectively) through the process of
  meiosis.
• Meiosis involves reductional division gamete
  cells contain only one set of 23 chromosomes (one
  of each of the 23 different pairs) and so is
  haploid, or n.

20
Useful References for Section 1

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• National Human Genome Research Institute Talking
  Glossary of Genetic Terms
• InfoTrac Learning about Sex from an Elegant
  Worm. Ascribe Higher Education News Service, Dec.
  15, 2005.
• InfoTrac Cell Growth, Division Genes Are
  Identified. UPI NewsTrack, Feb. 22, 2006.

21
Section 2

• A Closer Look at Chromosomes

22
A Closer Look at Chromosomes

• In a chromosome, DNA interacts with proteins.
• DNA is wound up on proteins called histones to
  form units called nucleosomes.
• Prior to division, each chromosome is duplicated
  to form two sister chromatids held together by a
  centromere.

Figure 19.3
23
In text Fig., p. 356
a One unduplicated chromosome
one chromatid
two sister chromatids
one chromatid
b One chromosome (duplicated)
24
A Closer Look at Chromosomes

• Spindles attach to chromosomes and move them.
• In both mitosis and meiosis, a cells
  chromosomes move into new positions with the help
  of the spindle.
• Two sets of microtubules extend from the cells
  two poles (the centrioles), overlapping at the
  spindles equator.

25
Fig. 19.4, p. 356
pole
one spindle microtubule
pole
26
Useful References for Section 2

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Major Advance Made on DNA Structure.
  Ascribe Higher Education News Service, May 2,
  2005.

27
Section 3

• The Cell Cycle

28
The Cell Cycle

• The cell cycle is a recurring sequence of events
  that extends from the time of a cells formation
  until its division is completed.
• Most of a cells existence is spent in
  interphase interphase consists of G1, S, and G2.

29
Fig. 19.5, p. 357
G1
Interval of cell growth, before DNA replication
(chromosomes unduplicated)
S
Interval of cell growth, when DNA replication is
completed (chromosomes duplicated)
Each daughter cell starts interphase
Cytoplasmic division
Telophase
G2
Anaphase
Interphase ends for parent cell
Metaphase
Interval following DNA replication cell
prepares to divide
Prophase
30
The Cell Cycle

• G1 gap during which most of the carbohydrates,
  lipids, and proteins for the cells own use are
  assembled.
• S synthesis phase when DNA is replicated.
• G2 second gap during which proteins that will
  drive mitosis are produced.
• M mitosis involving separation of the
  chromosomes followed by cytoplasmic division.
• The length of the cell cycle varies depending on
  cell type.

31
Fig. 19.6, p. 357
Cell at Interphase
nucleus
cytoplasm
Telophase
Prophase
Anaphase
Metaphase
32
Useful References for Section 3

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• Cells Alive The Cell Cycle
• InfoTrac Dutch Team Finds Aspects of Cell Cycle
  Checkpoints. Sharon Kingman. BioWorld
  International, Dec. 14, 2005.

33
Section 4

• The Four Stages
• of Mitosis

34
The Four Stages of Mitosis

• Mitosis begins with prophase.
• Chromosomes start condensing to become visible as
  rodlike units, each consisting of two sister
  chromatids joined at the centromere.
• The spindle starts forming from reassembled
  microtubules of the cytoskeleton.
• The spindle separates the centrioles to opposite
  poles of the cell.

35
The Four Stages of Mitosis

• Next comes metaphase.
• The nuclear membrane breaks up into tiny
  vesicles.
• Microtubules of the spindle interact with the
  chromosomes to orient the sister chromatids
  toward opposite poles.
• Overlapping spindle microtubules ratchet past
  each other, and soon all the chromosomes become
  aligned at the cells equator, halfway between
  the poles.

36
The Four Stages of Mitosis

• Anaphase, then telophase follows.
• Anaphase is marked by the separation of the
  sister chromatids and their movement toward
  opposite poles at the end of anaphase each
  chromatid is an independent chromosome.
• Microtubules attached to centromeres shorten,
  pulling the chromosomes to the poles.
• The spindle elongates, pushing the poles further
  apart.

37
The Four Stages of Mitosis

• Telophase begins when chromosomes arrive at the
  poles.
• The chromosomes, no longer attached to the
  microtubules, return to their threadlike form
  (they decondense).
• The nuclear envelope forms from the fusion of
  small vesicles mitosis is complete.
• In mitosis, each new cell has the same chromosome
  number as the parent nucleus.

38
Mitosis Prophase through Metaphase
Figure 19.7a-d
39
Mitosis Metaphase Through Telophase
Figure 19.7e-h
40
Useful References for Section 4

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Mitosis through the Microscope
  Advances in Seeing inside Live Dividing Cells.
  Science, April 4, 2003.

41
Section 5

• How the
• Cytoplasm Divides

42
How the Cytoplasm Divides

• Cytokinesis, the division of the cytoplasm,
  begins at the end of anaphase.
• Midway between poles, the plasma membrane sinks
  inward to form the cleavage furrow.
• Contractile microfilaments pull the plasma
  membrane inward to divide the cell in two.
• Each new cell has a
• nucleus, cytoplasm,
• and a plasma
• membrane.

Figure 19.8b
43
Cytokinesis
Figure 19.8a
44
Useful References for Section 5

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Measuring Protein Concentrations in
  Live Cells Yale Group Demonstrates New Method
  Using Cytokinesis. Sarah Rothman. The Scientist,
  Dec. 5, 2005.

45
Section 6

• Concerns and Controversies over Irradiation

46
Concerns and Controversies over Irradiation

• Irradiation effects on the body.
• Ionizing radiation includes radio waves, visible
  light, microwaves, cosmic rays, and radioactive
  radon gas.
• When it enters an
• organism, ionizing
• radiation can physically
• damage chromosomes,
• alter genes, or both.

Figure 19.9a
47
Concerns and Controversies over Irradiation

• Damaged chromosomes may not separate correctly
  damage in germ cells can lead to infants born
  with genetic defects.
• Sudden, large doses can destroy cells of the
  immune system, epithelial cells, and red blood
  cells, among other cell types.
• Low doses over long periods of time are less
  damaging due to repair mechanisms.
• Diagnostic technologies, despite the risks, are
  extremely useful.

48
Concerns and Controversies over Irradiation

• Irradiated food.
• Harmful pathogens can also be killed or damaged
  by ionizing radiation.
• Irradiation of foods (grains, fruits, meats) does
  not make them radioactive, but it does limit
  spoilage in addition to removing pathogens.
• Many people, however, still worry about the
  possible effects eating irradiated food might
  have over the long term.

49
Fig. 19.9b, p. 361
Appliances, other consumer products 3
Other 1
Nuclear medicine 4
Medical X rays 11
Radon 54
Chemical reactions in the body 11
Other chemical sources (non-radon) 8
Cosmic 8
50
Video Breast Cancer Treatment

• This video clip is available in CNN Today Videos
  for Anatomy and Physiology, 2003, Volume VII.
  Instructors, contact your local sales
  representative to order this volume, while
  supplies last.

51
Useful References for Section 6

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Food Irradiation May Start to Take Off.
  The Wichita Eagle, Jan. 8, 2006.
• U.S. Department of Energy Office of Human
  Radiation Experiments
• National Safety Council The Health Effects of
  Exposure to Indoor Radon

52
Section 7

• MeiosisThe Beginnings of Eggs and Sperm

53
Meiosis The Beginnings of Eggs and Sperm

• In meiosis there are two divisions.
• During interphase, a germ cell duplicates its
  DNA each duplicated chromosome consists of two
  sister chromatids attached to one another.

centromere
one chromatid
its sister chromatid
one chromosome in the duplicated state
In-text Fig., p. 362
54
Meiosis The Beginnings of Eggs and Sperm

• Interphase is followed by two consecutive
  divisions of the chromosomes there is no
  interphase between the two divisions.
• After each division, daughter cells form, giving
  rise to four haploid nuclei.
• The two divisions are called meiosis I and
  meiosis II.

55
In-text Fig., p. 362
MEIOSIS I
MEIOSIS II
no interphase ( no DNA replication before meiosis
II)
interphase ( DNA replication before meiosis I)
PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I
PROPHASE II METAPHASE II ANAPHASE II TELOPHASE
II
56
Meiosis The Beginnings of Eggs and Sperm

• During meiosis I, the homologous chromosomes
  first pair up, then separate from one another
  eventually the cytoplasm divides to produce two
  cells.
• Each of the two daughter
• cells receives a haploid
• number of chromosomes.
• Each chromosome is still
• duplicated.

Figure 19.12
57
Meiosis The Beginnings of Eggs and Sperm

• In meiosis II, the sister chromatids of each
  chromosome separate the cytoplasm divides again,
  resulting in four haploid cells.

Figure 19.12
58
Fig. 19.12 (1), p. 364
Meiosis I
Telophase I
Stepped Art
Prophase I
Metaphase I
Anaphase I
59
Fig. 19.12 (2), p. 365
Meiosis II
There is no DNA replication between the two
nuclear divisions.
Prophase II
Metaphase II
Anaphase II
Telophase II
Stepped Art
60
Meiosis The Beginnings of Eggs and Sperm

• Meiosis is the first step in the formation
• of gametes.
• In males, meiosis and gamete formation are called
  spermatogenesis.
• Germ cell (2n) gtgtgt primary spermatocyte (2n) gtgtgt
  MEIOSIS I gtgtgt two secondary spermatocytes (n) gtgtgt
  MEIOSIS II gtgtgt four spermatids (n).
• Spermatids change in form each develops a tail
  to become mature sperm.

61
In-text Fig., p. 362
multicellular body
mitosis
zygote
Diploid
meiosis
fertilization
Haploid
gametes
62
Fig. 19.10, p. 363
cell differentiation, sperm formation (mature,
haploid male gametes)
secondary spermatocytes (haploid)
spermato-gonium (diploid male germ cell )
primary spermatocyte (diploid)
spermatids (haploid)
a. Growth
b. Meiosis I and cytokenesis
c. Meiosis II and cytokinesis
63
Meiosis The Beginnings of Eggs and Sperm

• In females, meiosis and gamete formation are
  called oogenesis.
• Germ cell (2n) gtgtgt primary oocyte (2n) gtgtgt
  MEIOSIS I gtgtgt secondary oocyte (n, and large in
  size) plus polar body (n, and small in size) gtgtgt
  MEIOSIS II gtgtgt one large ovum (n) plus three
  polar bodies (n, small).
• Primary oocytes arrest in prophase I until
  puberty then, each ovarian cycle, one oocyte
  completes meiosis I to become arrested in
  metaphase II.
• If the secondary oocyte is fertilized meiosis II
  continues.
• The single ovum is the only cell capable of being
  fertilized by a sperm the polar bodies wither
  and die.

64
Fig. 19.11, p. 363
three polar bodies (haploid)
first polar body (haploid)
oogonium (diploid female germ cell)
primary oocyte (diploid)
secondary oocyte (haploid)
ovum (haploid)
b. Meiosis I and cytokinesis
c. Meiosis II and cytokinesis
a. Growth
65
How the Chromosome Number Changes in Meiosis
Figures 19.17 and 19.18
66
Useful References for Section 7

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Neonatal Outcome of Preimplantation
  Genetic Diagnosis by Polar Body Removal. Charles
  M. Strom et al. Pediatrics, Oct. 2000.

67
Section 8

• A Visual Tour of the Stages of Meiosis

68
Meiosis I
Figure 19.12a-d
69
Meiosis II
Figure 19.12e-h
70
Useful References for Section 8

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Association between Maternal Age and
  Meiotic Recombination for Trisomy 21. Neil E.
  Lamb et al. American Journal of Human Genetics,
  Jan. 2005.

71
Section 9

• The Second Stage of MeiosisNew Combinations of
  Parents Traits

72
The Second Stage of MeiosisNew Combinations of
Parents Traits

• In prophase I, genes may be rearranged.
• During condensation of chromosomes, homologues
  are stitched together tightly in a side-by-side
  alignment that favors crossing over.
• Nonsister chromatids cross over, break, and
  reform at the breaks, they exchange genetic
  segments.
• Each gene can have alternate forms called
  alleles these alleles can be swapped during
  crossing over to create new combinations of
  alleles.
• Genetic recombination (exchange of alleles) is
  one source of genetic variation.

73
a Both chromosomes shown here were duplicated
during interphase, before meiosis. When prophase
I is under way, sister chromatids of each
chromosome are posistioned so close together that
they look like a single thread.
b Each chromosome becomes zippered to its
homologue, so all four chromatids are tightly
aligned. If the two sex chomosomes have
different forms, such as X paired with Y, they
still get zippered together, but only in a tiny
region at their ends.
c We show the pair of chromosomes as if they
already condensed only to give you an idea of
what goes on. They really are in a tightly
aligned, threadlike form during prophase I.
d The intimate contact encourages at least one
crossover to happen at various intervals along
the length of nonsister chromatids.
e Nonsister chromatids exchange segments at the
crossover sites. They continue to condense into
thicker, rodlike forms. By the start of
metaphase I, they will be unzippered from each
other.
f Crossing over breaks up old combinations of
genes and puts new ones together in the cells
pairs of homologous chromosomes.
Fig. 19.13, p. 366
74
The Second Stage of MeiosisNew Combinations of
Parents Traits

• In metaphase I, maternal and paternal chromosomes
  are shuffled.
• During metaphase I, homologous chromosomes
  randomly line up at the spindle equator.
• During anaphase I, the homologous chromosomes
  separate into two haploid cells, each of which
  has a
• random mix of maternal and paternal chromosomes.
• Random alignment of chromosomes adds to genetic
  variation.

75
Fig. 19.14, p. 367
1
2
3
combinations possible
or
or
or
76
The Second Stage of MeiosisNew Combinations of
Parents Traits

• Disjunction is a term used to describe the
  separation of homologues from their partners
  during anaphase I failure to separate can lead
  to birth defects.

77
Useful References for Section 9

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Sex, Not Genotype, Determines
  Recombination Levels in Mice. Audrey Lynn et al.
  American Journal of Human Genetics, Oct. 2005.

78
Section 10

• Meiosis and Mitosis Compared

79
Meiosis and Mitosis Compared

• Mitotic cell division produces clones this type
  of division provides for growth of the body and
  replacement of lost cells.
• Meiosis occurs only in the germ cells used in
  sexual reproduction meiosis promotes genetic
  variation in three ways.
• Prophase I rearranges alleles by crossing over.
• Metaphase I allows for random assortment of
  maternal and paternal chromosomes.
• Chance brings together different combinations of
  genes through fertilization.

80
Meiosis I
Figure 19.15
81
Mitosis vs. Meiosis II
Figure 19.15
82
Useful References for Section 10

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Absence of Age Effect on Meiotic
  Recombination between Human X and Y Chromosomes.
  Qinghua Shi et al. American Journal of Human
  Genetics, Aug. 2002.
• PBS How Cells Divide Mitosis vs. Meiosis