1. Ch. 8 The Cellular Basis of Reproduction and Inheritance
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2. Cell division plays many important roles in the lives of organisms
Living organisms reproduce by two methods.
Asexual reproduction
offspring are identical to the parent
involves inheritance of all genes from one parent.
Sexual reproduction
offspring are similar to the parents, but show variations in traits
involves inheritance of unique sets of genes from two parents. 2

3. Cell division plays many important roles in the lives of organisms
Cell division is reproduction at the cellular level,
Requires duplication of chromosomes, sorting new sets of chromosomes into the resulting pair of daughter cells.
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4. Cell division plays many important roles in the lives of organisms
Cell division is used for:
Reproduction of single-celled organisms
Growth of multicellular organisms from a fertilized egg into an adult,
Repair and replacement of cells
Sperm and egg production.
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5. Prokaryotes reproduce by binary fission
Prokaryotes (bacteria and archaea) reproduce by binary fission “dividing in half”
Binary Fission Occurs in Three Steps:
duplication of the chromosome and separation of the copies,
continued elongation of the cell and movement of the copies
division into two daughter cells.
The chromosome of a prokaryote is:
A singular circular DNA molecule & associated proteins
Much smaller than eukaryotic DNA
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6. Division into two daughter cells
Figure 8.2A_s3
Plasma
membrane
Prokaryotic
chromosome
Cell wall
Duplication of the chromosome
and separation of the copies 1
Continued elongation of the
cell and movement of the copies 2
Division into
two daughter cells 3 6

7. THE EUKARYOTIC CELL CYCLE AND MITOSIS
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8. The large, complex chromosomes of eukaryotes duplicate with each cell division
Eukaryotic cells have more genes, and store most of their genes on multiple chromosomes within the nucleus.
Eukaryotic chromosomes are composed of chromatin = one long DNA molecule and proteins
Before dividing chromatin becomes highly compact (into chromosomes) and visible with a microscope
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9. Chromosomes DNA molecules Sister chromatids Chromosome duplication
Figure 8.3B
Chromosomes
DNA molecules
Sister
chromatids
Chromosome
duplication
Sister
chromatids
Centromere
Chromosome
distribution
to the
daughter
cells 9

10. The large, complex chromosomes of eukaryotes duplicate with each cell division
Before a eukaryotic cell divides, it duplicates all of its chromosomes, resulting in two copies called sister chromatids joined together by a narrowed “waist” called the centromere.
When a cell divides, the sister chromatids separate from each other, (now called chromosomes) and sort into separate daughter cells.
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11. Chromosomes DNA molecules Chromosome duplication Sister chromatids
Figure 8.3B_1
Chromosomes
DNA molecules
Chromosome
duplication
Sister
chromatids
Centromere
Chromosome
distribution
to the
daughter
cells 11

12. The cell cycle multiplies cells
The cell cycle extends from the time a cell is first formed until its own division.
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13. The cell cycle multiplies cells
The cell cycle consists of two stages, characterized as follows:
Interphase: duplication of cell contents
G1—growth, increase in cytoplasm
S—duplication of chromosomes
G2—growth, preparation for division
Mitotic phase: nuclear division
Mitosis—division of the chromosomes in ucleus
Cytokinesis—division of cytoplasm
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14. I N T E R P H A S G1 (first gap) S (DNA synthesis) M G2 (second gap)
Cytokinesis G2
(second gap)
Mitosis T MI O IC PH A SE 14

15. Cell division is a continuum of dynamic changes
Mitosis progresses through a series of stages (nuclear division):
prophase
prometaphase
metaphase
anaphase
telophase.
Cytokinesis often overlaps telophase.
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16. (with centriole pairs) Fragments of the nuclear envelope Early mitotic
MITOSIS
INTERPHASE
Prophase
Prometaphase
Centrosomes
(with centriole pairs)
Fragments of
the nuclear
envelope
Early mitotic
spindle
Centrosome
Kinetochore
Centrioles
Chromatin
Figure 8.5_1 The stages of cell division by mitosis: Interphase through Prometaphase
Centromere
Nuclear
envelope
Plasma
membrane
Chromosome,
consisting of two
sister chromatids
Spindle
microtubules 16

17. Cell division is a continuum of dynamic changes
Prophase
In the cytoplasm microtubules begin to emerge from centrosomes, forming the mitotic spindle.
In the nucleus chromosomes coil and become compact and visible with a light microscope
Nucleoli disappear.
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18. Cell division is a continuum of dynamic changes
Prometaphase
Spindle microtubules attach at kinetochores on centromeres of sister chromatids and move chromosomes to the center of the cell
The nuclear envelope disappears.
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19. Telophase and Cytokinesis
MITOSIS
Metaphase
Anaphase
Telophase and Cytokinesis
Metaphase
plate
Cleavage
furrow
Nuclear
envelope
forming
Mitotic
spindle
Daughter
chromosomes 19

20. Cell division is a continuum of dynamic changes
Metaphase
The mitotic spindle is fully formed and chromosomes align at the cell equator.
Kinetochores of sister chromatids are facing the opposite poles of the spindle.
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21. Cell division is a continuum of dynamic changes
Anaphase
Sister chromatids separate at centromeres and daughter chromosomes are moved to opposite poles of the cell
The cell elongates due to lengthening of nonkinetochore microtubules.
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22. Cell division is a continuum of dynamic changes
Telophase
The cell continues to elongate and nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei
Chromatin uncoils and nucleoli reappear.
The spindle disappears.
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23. Cell division is a continuum of dynamic changes
Cytokinesis differs in animal and plant cells.
In animal cells a cleavage furrow forms from a contracting ring of microfilaments, interacting with myosin; the cleavage furrow deepens to separate the contents into two cells.
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24. In plant cells a cell plate forms in the middle, from vesicles containing cell wall material; the cell plate grows outward to reach the edges, dividing the contents into two cells, each with a plasma membrane and cell wall.
New
cell wall
Cell wall
of the
parent cell
Cell wall
Plasma
membrane
Daughter
nucleus
Vesicles
containing
cell wall
material
Cell plate
Daughter
cells
Cell plate
forming
Cytokinesis 24

25. Anchorage, cell density, and chemical growth factors affect cell division
The cells within an organism’s body divide and develop at different rates.
Cell division is controlled by
the presence of essential nutrients
growth factors, proteins that stimulate division
density-dependent inhibition, in which crowded cells stop dividing
anchorage dependence, the need for cells to be in contact with a solid surface to divide.
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26. Cultured cells
suspended in liquid
The addition of
growth
factor 26

27. Anchorage Single layer of cells Removal of cells Restoration of single
layer by cell
division 27

28. Growth factors signal the cell cycle control system
There are three major checkpoints in the cell cycle.
G1 checkpoint
allows entry into the S phase or causes the cell to leave the cycle, entering a nondividing G0 phase.
G2 checkpoint
M checkpoint.
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29. G1 checkpoint G0 G1 S Control system M G2 M checkpoint G2 checkpoint
Figure 8.8A A schematic model for the cell cycle control system G2
M checkpoint
G2 checkpoint 29

30. G1 checkpoint Receptor protein S G1 Control system M G2
EXTRACELLULAR FLUID
Plasma membrane
Growth
factor
Relay proteins G1
checkpoint
Receptor
protein
Signal
transduction
pathway S G1
Control
system M G2
CYTOPLASM 30

31. CONNECTION: Growing out of control, cancer cells produce malignant tumors
Cancer cells escape controls on the cell cycle.
Cancer cells divide rapidly, often in the absence of growth factors, spread to other tissues through the circulatory system, and grow without being inhibited by other cells.
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32. CONNECTION: Growing out of control, cancer cells produce malignant tumors
A tumor is an abnormally growing mass of body cells.
Benign tumors remain at the original site.
Malignant tumors spread to other locations, a process called metastasis.
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33. Lymph vessels Blood vessel Tumor Tumor in another part of the body
Glandular
tissue
Figure 8.9 Growth and metastasis of a malignant (cancerous) tumor of the breast
Growth
Invasion
Metastasis 33

34. MEIOSIS AND CROSSING OVER
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35. Chromosomes are matched in homologous pairs
In humans, body (somatic) cells have 23 pairs of homologous chromosomes: One member of each is from each parent.
One pair = sex chromosomes = X and Y; they differ in size and genetic composition.
The other 22 pairs of chromosomes are autosomes; they have the same size and genetic composition. 35

36. Chromosomes are matched in homologous pairs
Homologous chromosomes are matched in length, centromere position, and gene locations (except X & Y)
A locus (plural, loci) is the position of a gene.
Different versions of a gene may be found at the same locus on maternal and paternal chromosomes = alleles
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37. Locus Pair of homologous chromosomes Centromere Sister chromatids
Figure 8.11 A pair of homologous chromosomes
One duplicated
chromosome 37

38. Gametes have a single set of chromosomes
Humans and many animals and plants are diploid meaning that their body cells that have two sets of chromosomes, one from each parent.
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39. Gametes have a single set of chromosomes
Meiosis is a process that converts diploid nuclei to haploid nuclei.
Diploid cells have two homologous sets of chromosomes.
Haploid cells have one set of chromosomes.
Meiosis occurs in sex organs, producing gametes: sperm and eggs.
Fertilization is the union of sperm and egg.
The zygote has a diploid chromosome number, one set from each parent.
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40. Multicellular diploid adults (2n  46) Diploid stage (2n)
Haploid gametes (n  23) n
Egg cell n
Sperm cell
Meiosis
Fertilization
Ovary
Testis
Figure 8.12A The human life cycle
Diploid
zygote
(2n  46) 2n
Key
Mitosis
Haploid stage (n)
Multicellular diploid
adults (2n  46)
Diploid stage (2n) 40

41. Sister chromatids A pair of homologous chromosomes in a diploid
INTERPHASE
MEIOSIS I
MEIOSIS II
Sister
chromatids 1 2 3
A pair of
homologous
chromosomes
in a diploid
parent cell
A pair of
duplicated
homologous
chromosomes
Figure 8.12B How meiosis halves chromosome number 41

42. Meiosis reduces the chromosome number from diploid to haploid
Meiosis I – Prophase I – events occurring in the nucleus.
Chromosomes coil and become compact.
Homologous chromosomes come together as pairs by synapsis.
Each pair, with four chromatids, is called a tetrad.
Nonsister chromatids exchange genetic material by crossing over.
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43. Chromosomes duplicate Prophase I
MEIOSIS I
INTERPHASE:
Chromosomes duplicate
Prophase I
Centrosomes
(with centriole
pairs)
Sites of crossing over
Centrioles
Spindle
Figure 8.13_1 The stages of meiosis: Interphase to Prophase I
Tetrad
Chromatin
Sister
chromatids
Nuclear
envelope
Fragments
of the
nuclear
envelope 43

44. attached to a kinetochore Sister chromatids remain attached
MEIOSIS I
Metaphase I
Anaphase I
Spindle microtubules
attached to a kinetochore
Sister chromatids
remain attached
Figure 8.13_2 The stages of meiosis: Metaphase I to Anaphase I
Centromere
(with a
kinetochore)
Metaphase
plate
Homologous
chromosomes
separate 44

45. Meiosis reduces the chromosome number from diploid to haploid
Meiosis I – Metaphase I – Tetrads align at the cell equator.
Meiosis I – Anaphase I – Homologous pairs separate and move toward opposite poles of the cell.
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46. Meiosis reduces the chromosome number from diploid to haploid
Meiosis I – Telophase I - Duplicated chromosomes have reached the poles, a nuclear envelope re-forms around chromosomes in some species, each nucleus has the haploid number of chromosomes.
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47. Meiosis reduces the chromosome number from diploid to haploid
Meiosis II follows meiosis I without chromosome duplication.
Each of the two haploid products enters meiosis II.
Meiosis II – Prophase II
Chromosomes coil and become compact (if uncoiled after telophase I).
Nuclear envelope, if re-formed, breaks up again.
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48. Figure 8.13_right
MEIOSIS II: Sister chromatids separate
Telophase II
and Cytokinesis
Telophase I and Cytokinesis
Prophase II
Metaphase II
Anaphase II
Cleavage
furrow
Sister chromatids
separate
Haploid daughter
cells forming
Figure 8.13_right The stages of meiosis: Telophase I and Meiosis II 48

49. MEIOSIS II: Sister chromatids separate
Figure 8.13_4
MEIOSIS II: Sister chromatids separate
Telophase II
and Cytokinesis
Prophase II
Metaphase II
Anaphase II
Sister chromatids
separate
Haploid daughter
cells forming
Figure 8.13_4 The stages of meiosis: Meiosis II 49

50. Meiosis reduces the chromosome number from diploid to haploid
Meiosis II – Metaphase II – Duplicated chromosomes align at the cell equator.
Meiosis II – Anaphase II sister chromatids separate and chromosomes move toward opposite poles.
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51. Meiosis reduces the chromosome number from diploid to haploid
Meiosis II – Telophase II Chromosomes have reached the poles of the cell, a nuclear envelope forms around each set of chromosomes, with cytokinesis, four haploid cells are produced.
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52. Mitosis and meiosis have important similarities and differences
Mitosis and meiosis both
begin with diploid parent cells that
have chromosomes duplicated during interphase.
However the end products differ.
Mitosis produces two genetically identical diploid somatic daughter cells.
Meiosis produces four genetically unique haploid gametes.
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53. (before chromosome duplication)
Figure 8.14
MITOSIS
MEIOSIS I
Parent cell
(before chromosome duplication)
Prophase
Site of
crossing
over
Prophase I
Duplicated
chromosome
(two sister
chromatids)
Tetrad formed
by synapsis of
homologous
chromosomes
Chromosome
duplication
Chromosome
duplication
2n  4
Metaphase
Metaphase I
Chromosomes
align at the
metaphase plate
Tetrads (homologous
pairs) align at the
metaphase plate
Anaphase
Telophase
Anaphase I
Telophase I
Homologous
chromosomes
separate during
anaphase I;
sister
chromatids
remain together
Figure 8.14 Comparison of mitosis and meiosis
Sister chromatids
separate during
anaphase
Daughter
cells of
meiosis I
Haploid
n  2
MEIOSIS II 2n 2n
No further
chromosomal
duplication;
sister
chromatids
separate during
anaphase II
Daughter cells of mitosis n n n n
Daughter cells of meiosis II 53

54. (before chromosome duplication)
Figure 8.14_1
MITOSIS
MEIOSIS I
Parent cell
(before chromosome duplication)
Prophase
Prophase I
Site of
crossing
over
Chromosome
duplication
Chromosome
duplication
Tetrad
2n  4
Metaphase
Metaphase I
Figure 8.14_1 Comparison of mitosis and meiosis (part 1)
Chromosomes
align at the
metaphase plate
Tetrads (homologous
pairs) align at the
metaphase plate 54

55. Sister chromatids separate during anaphase
Figure 8.14_2
MITOSIS
Metaphase
Chromosomes
align at the
metaphase plate
Anaphase
Telophase
Figure 8.14_2 Comparison of mitosis and meiosis (part 2)
Sister chromatids
separate during
anaphase 2n 2n
Daughter cells of mitosis 55

56. Daughter cells of meiosis II
Figure 8.14_3
MEIOSIS I
Metaphase I
Tetrads (homologous
pairs) align at the
metaphase plate
Anaphase I
Telophase I
Homologous
chromosomes
separate during
anaphase I;
sister
chromatids
remain together
Daughter
cells of
meiosis I
Haploid
n  2
Figure 8.14_3 Comparison of mitosis and meiosis (part 3)
MEIOSIS II
No further
chromosomal
duplication;
sister
chromatids
separate during
anaphase II n n n n
Daughter cells of meiosis II 56

57. Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring
Genetic variation in gametes results from independent orientation at metaphase I and random fertilization.
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58. Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring
Independent orientation at metaphase I
Each pair of chromosomes independently aligns at the cell equator.
There is an equal probability of the maternal or paternal chromosome facing a given pole.
The number of combinations for chromosomes packaged into gametes is 2n where n = haploid number of chromosomes.
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59. Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring
Random fertilization – The combination of each unique sperm with each unique egg increases genetic variability.
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60. Two equally probable arrangements of chromosomes at metaphase I
Possibility A
Possibility B
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Figure 8.15_s3 Results of the independent orientation of chromosomes at metaphase I (step 3)
Gametes
Combination 1
Combination 2
Combination 3
Combination 4 60

61. Crossing over further increases genetic variability
Genetic recombination is the production of new combinations of genes due to crossing over.
Crossing over is an exchange of corresponding segments between nonsister chromatids on homologous chromosomes.
Nonsister chromatids join at a chiasma (plural, chiasmata), the site of attachment and crossing over. .
Chiasma
Tetrad
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62. ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE
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63. A karyotype is a photographic inventory of an individual’s chromosomes
A karyotype is an ordered display of magnified images of an individual’s chromosomes arranged in pairs.
Karyotypes
are often produced from dividing cells arrested at metaphase of mitosis and
allow for the observation of
homologous chromosome pairs,
chromosome number, and
chromosome structure.
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64. Packed red Hypotonic and white solution Fixative blood cells Blood
Figure 8.18_s3
Packed red
and white
blood cells
Hypotonic
solution
Fixative
Blood
culture
Stain
White
blood
cells
Centrifuge 2 3
Figure 8.18_s3 Preparation of a karyotype from a blood sample (step 3)
Fluid 1 64

65. Figure 8.18_s4 Preparation of a karyotype from a blood sample (step 4)65

66. Centromere Sister chromatids Pair of homologous chromosomes
Figure 8.18_s5 Preparation of a karyotype from a blood sample (step 5) 5
Sex chromosomes 66

67. An extra copy of chromosome 21 causes Down syndrome
Trisomy called Down syndrome, produces a characteristic set of symptoms, which include:
mental retardation,
characteristic facial features,
short stature,
involves the inheritance of three copies of chromosome 21 andis the most common human chromosome abnormality.
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68. Figure 8.19A
Figure 8.19A A karyotype showing trisomy 21, and an individual with Down syndrome
Trisomy 21 68

69. Accidents during meiosis can alter chromosome number
Nondisjunction is the failure of chromosomes or chromatids to separate normally during meiosis. This can happen during
meiosis I, if both members of a homologous pair go to one pole or
meiosis II if both sister chromatids go to one pole.
Fertilization after nondisjunction yields zygotes with altered numbers of chromosomes.
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70. MEIOSIS I Nondisjunction MEIOSIS II Normal meiosis II Gametes
Figure 8.20A_s3
MEIOSIS I
Nondisjunction
MEIOSIS II
Normal
meiosis II
Figure 8.20A_s3 Nondisjunction in meiosis I (step 3)
Gametes
Number of
chromosomes
n  1
n  1
n  1
n  1
Abnormal gametes 70

71. MEIOSIS I Normal meiosis I MEIOSIS II Nondisjunction n  1 n  1 n n
Figure 8.20B_s3
MEIOSIS I
Normal
meiosis I
MEIOSIS II
Nondisjunction
Figure 8.20B_s3 Nondisjunction in meiosis II (step 3)
n  1
n  1 n n
Abnormal gametes
Normal gametes 71

72. Alterations of chromosome structure can cause birth defects and cancer
Chromosome breakage can lead to rearrangements that can produce
genetic disorders or, if changes occur in somatic cells, cancer.
These rearrangements may include
a deletion, the loss of a chromosome segment,
a duplication, the repeat of a chromosome segment,
an inversion, the reversal of a chromosome segment, or
a translocation, the attachment of a segment to a nonhomologous chromosome that can be reciprocal 72

73. Alterations of chromosome structure can cause birth defects and cancer
Chronic myelogenous leukemia (CML)
is one of the most common leukemias,
affects cells that give rise to white blood cells (leukocytes), and
results from part of chromosome 22 switching places with a small fragment from a tip of chromosome 9.
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74. Reciprocal translocation
Deletion
Inversion
Duplication
Reciprocal translocation
Homologous
chromosomes
Nonhomologous
chromosomes
Figure 8.23A Alterations of chromosome structure 74

75. Activated cancer-causing gene
Chromosome 9
Reciprocal
translocation
Chromosome 22
Activated cancer-causing gene
Figure 8.23B The translocation associated with chronic myelogenous leukemia
“Philadelphia chromosome” 75

76. Mitosis Meiosis Number of chromosomal duplications
Number of cell divisions
Number of daughter cells
produced
Number of chromosomes in
the daughter cells
How the chromosomes line
up during metaphase
Figure 8.UN03 Connecting the Concepts, question 1
Genetic relationship of the
daughter cells to the parent cell
Functions performed in the
human body 76