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
Cell division is reproduction at the cellular level
Requires duplication (DNA replication) of chromosomes
Sorting the new sets of chromosomes into the resulting pair of daughter cells.
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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3. Prokaryotes reproduce by binary fission
Prokaryotes reproduce by binary fission or “dividing in half”
Binary Fission Occurs in Three Steps:
Duplication of the chromosome and separation of the copies
Elongation of the cell and movement of the copies
Continued elongation and division into two daughter cells.
The chromosome of a prokaryote is:
A single circular DNA molecule & associated proteins
Much smaller than eukaryotic DNA
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4. Cell division plays many important roles in the lives of organisms
Living Organisms Reproduce by Two Methods
Asexual reproduction
Does not involve the fusion of sperm & egg
Offspring (daughter cells) are produced when one parent cell undergoes cell division (includes mitosis)
Offspring inherit all genes from one parent, therefore are identical to the parent
Sexual reproduction
Involves the production of sex cells (sperm & egg) through a process called meiosis
Offspring are produced by the fusion of sperm & egg (fertilization)
Offspring look similar to parents, but show variations in traits
Offspring inherit a unique set of genes from their two parents. 4

5. THE EUKARYOTIC CELL CYCLE AND MITOSIS
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6. The large complex chromosomes of eukaryotes duplicate before the cell divides
Eukaryotic cells store most of their genes on multiple chromosomes within the nucleus.
Eukaryotic chromosomes are organized as chromatin = one long, filament like DNA molecule and proteins
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7. The large complex chromosomes of eukaryotes duplicate before the cell divides
Before a eukaryotic cell divides, it duplicates all of its chromosomes, resulting in two copies called sister chromatids joined by a centromere.
When a cell divides, sister chromatids separate from each other, (now called chromosomes) and sort into separate daughter cells.
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8. Duplication of Chromosomes
DNA molecules
Sister
chromatids
Chromosome
duplication
Sister
chromatids
Centromere
Figure 8.3B Chromosome duplication and distribution
Chromosome
distribution
to the
daughter
cells 8

9. Cells Divide to Produce More cells during the Cell Cycle
The Cell Cycle occurs in two stages:
Interphase:
Gap 1 (G1) phase—growth & increase in cytoplasm
Synthesis (S) phase—duplication of chromosomes (DNA replication)
Gap 2 (G2) phase—growth & preparation for division
Mitotic Phase (Mitosis):
Division of chromosomes in the nucleus
Followed by division of the cytoplasm or cytokinesis
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10. Cell division is a Continuum of Dynamic Changes
Mitosis progresses through a series of stages in the following order:
Prophase/Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
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11. (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 11

12. Telophase and Cytokinesis
MITOSIS
Metaphase
Anaphase
Telophase and Cytokinesis
Metaphase
plate
Cleavage
furrow
Figure 8.5_5 The stages of cell division by mitosis: Metaphase through Cytokenesis
Nuclear
envelope
forming
Mitotic
spindle
Daughter
chromosomes 12

13. Cell division is a Continuum of Dynamic Changes
Prophase
Microtubules (mitotic spindle) begin to emerge from centrosomes
Spindle microtubules attach to kinetochores, moving chromosomes towards center of the cell
Chromatin condenses into chromosomes (now visible with a light microscope)
Nucleoli, nuclear envelope disappear
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14. Cell division is a Continuum of Dynamic Changes
Metaphase
Chromosomes align at the cell equator in preparation for division
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15. 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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16. Cell division is a Continuum of Dynamic Changes
Telophase
The cell continues to elongate
The nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei
Chromosomes uncoil and nucleoli reappear
The spindle disappears
Teaching Tips
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17. Cytokinesis in Animal Cells
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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18. Cytokinesis in Plant Cells
Cell wall
of the
parent cell
New cell wall
Cell wall
Plasma
membrane
Daughter
nucleus
Cell plate
forming
Vesicles
containing
cell wall
material
Cell plate
Daughter
cells
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.
Figure 8.6B Cell plate formation in a plant cell 18

19. 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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20. Cultured cells suspended in liquid The addition of growth factor
Figure 8.7A An experiment demonstrating the effect of growth factors on the division of cultured animal cells 20

21. 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
Figure 8.8B How a growth factor signals the cell cycle control system M G2
CYTOPLASM 21

22. Anchorage Single layer of cells Removal of cells Restoration of single
Figure 8.7B An experiment demonstrating density-dependent inhibition, using animal cells grown in culture
Restoration
of single
layer by cell
division 22

23. CONNECTION: Growing out of control, cancer cells produce malignant tumors
Cancer cells escape controls of 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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24. 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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25. 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 25

26. MEIOSIS AND CROSSING OVER
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27. Chromosomes are Matched in Homologous Pairs
Humans and many animals & plants are diploid meaning that their body cells have two sets of chromosomes, one set from each parent.
Human body (somatic) cells are diploid, containing a total of 46 chromosomes arranged as 23 homologous pairs.
One pair of chromosomes = sex chromosomes = X and Y; they differ in size and genetic composition.
The other 22 pairs of chromosomes = autosomes; they have the same size and genetic composition. 27

28. 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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29. Locus Pair of homologous chromosomes Centromere Sister chromatids
Figure 8.11 A pair of homologous chromosomes
One duplicated
chromosome 29

30. Gametes Have a Single Set of Chromosomes
Meiosis is a process that converts diploid nuclei to haploid nuclei.
Diploid cells have two homologous chromosomes present
Haploid cells have one set of chromosomes
Meiosis occurs in sex organs, producing gametes (sperm and egg)
Fertilization is the union of sperm and egg.
The resulting zygote has a diploid chromosome number, having received one set of chromosomes from each parent.
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31. 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) 31

32. Stages of Meiosis
Meiosis I – Prophase I – events occurring in the nucleus.
Chromatin condenses
Homologous chromosomes synapse and the pairs, with four chromatids, is called a tetrad
Nonsister chromatids exchange genetic material by crossing over
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33. 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
Chiasma
Tetrad
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34. 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 34

35. 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 35

36. Stages of Meiosis Meiosis I
Meiosis I
Metaphase I – Tetrads align at the cell equator
Anaphase I – Homologous pairs separate and move toward opposite poles of the cell
Telophase I /cytokinesis- Duplicated chromosomes have reached the poles, a nuclear envelope re-forms around chromosomes
Each nucleus has the haploid number of chromosomes
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37. Meiosis II follows meiosis I without chromosome duplication
The two haploid cells enter meiosis II.
MEIOSIS II
INTERPHASE
MEIOSIS I 2
Sister
chromatids 1 2
A pair of
homologous
chromosomes
in a diploid
parent cell
Figure 8.12B How meiosis halves chromosome number
A pair of
duplicated
homologous
chromosomes 37

38. Stages of Meiosis Meiosis II Interphase II
Prophase II- Chromosomes coil and become compact (if uncoiled after telophase I)
Nuclear envelope, if re-formed, breaks up again
Metaphase II – Duplicated chromosomes align at the cell equator
Anaphase II sister chromatids separate and chromosomes move toward opposite poles
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

39. 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 39

40. 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 40

41. Mitosis and Meiosis have Important Similarities and Differences
Mitosis and meiosis both
Begin with diploid parent cells
Have chromosomes that are duplicated once during interphase
The end products of mitosis and meiosis differ
Mitosis produces two genetically identical diploid somatic daughter cells
Meiosis produces four genetically unique haploid gametes
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42. (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 42

43. Meiosis

44. Independent Orientation of Chromosomes in Meiosis and Random Fertilization lead to Varied Offspring
Genetic variation in gametes produced by meiosis results from independent orientation at metaphase I and random fertilization
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45. 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 moving towards a given pole
The number of combinations for chromosomes packaged into gametes is 2n where n = haploid number of chromosomes
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46. 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 46

47. 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 in the offspring
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48. ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE
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49. 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
Karyotypes allow for the observation of
homologous chromosome pairs
chromosome number, sex
chromosome structure
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50. 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 50

51. Figure 8.18_s4 Preparation of a karyotype from a blood sample (step 4)51

52. Centromere Sister chromatids Pair of homologous chromosomes
Figure 8.18_s5 Preparation of a karyotype from a blood sample (step 5) 5
Sex chromosomes 52

53. An Extra Copy of Chromosome 21 causes Down Syndrome
Trisomy 21 called Down syndrome, produces a characteristic set of symptoms, which include:
characteristic facial features
short stature
involves the inheritance of three copies of chromosome 21 and is the most common human chromosome abnormality.
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54. Figure 8.19A
Figure 8.19A A karyotype showing trisomy 21, and an individual with Down syndrome
Trisomy 21 54

55. 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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56. 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 56

57. 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 57

58. Alterations of Chromosome Structure can Cause Birth Defects and Cancer
Chromosome breakage can lead to rearrangements that can produce
genetic disorders or, cancer if changes occur in somatic cells,
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 58

59. Chronic Myelogenous Leukemia (CML)
A common leukemia that 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.
Chromosome 9
Chromosome 22
Reciprocal
translocation
Figure 8.23B The translocation associated with chronic myelogenous leukemia
Activated cancer-causing gene
“Philadelphia chromosome” 59

60. Reciprocal translocation
Deletion
Inversion
Duplication
Reciprocal translocation
Homologous
chromosomes
Nonhomologous
chromosomes
Figure 8.23A Alterations of chromosome structure 60

61. 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 61