1. Cell Division -- The Cellular Basis of Reproduction and Inheritance
Cytology
Cell Division -- The Cellular Basis of Reproduction and Inheritance

2. In sexual reproduction
Fertilization of sperm and egg produces offspring
In asexual reproduction
Offspring are produced by a single parent, without the participation of sperm and egg

3. CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION
8.1 Like begets like, more or less
Some organisms reproduce asexually
And their offspring are genetic copies of the parent and of each other
LM 340
Figure 8.1A

4. Other organisms reproduce sexually Creating a variety of offspring
Figure 8.1B

5. 8.2 Cells arise only from preexisting cells
Cell division is at the heart of the reproduction of cells and organisms
Because cells come only from preexisting cells

6. 8.3 Prokaryotes reproduce by binary fission
Prokaryotic cells
Reproduce asexually by cell division
Colorized TEM 32,500
Prokaryotic chromosomes
Figure 8.3B

7. Division into two daughter cells
As the cell replicates its single chromosome, the copies move apart
And the growing membrane then divides the cells
Plasma membrane
Prokaryotic chromosome
Cell wall
Duplication of chromosome and separation of copies 1
Continued elongation of the cell and movement of copies 2
Division into two daughter cells 3
Figure 8.3A

8. THE EUKARYOTIC CELL CYCLE AND MITOSIS
8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division
A eukaryotic cell has many more genes than a prokaryotic cell
And they are grouped into multiple chromosomes in the nucleus

9. And are visible only when the cell is in the process of dividing
Individual chromosomes contain a very long DNA molecule associated with proteins
And are visible only when the cell is in the process of dividing
If a cell is not undergoing division
Chromosomes occur in the form of thin, loosely packed chromatin fibers
LM 600
Figure 8.4A

10. Before a cell starts dividing, the chromosomes replicate
Producing sister chromatids joined together at the centromere
TEM 36,000
Centromere
Sister chromatids
Figure 8.4B

11. Chromosome distribution to daughter cells
Cell division involves the separation of sister chromatids
And results in two daughter cells, each containing a complete and identical set of chromosomes
Centromere
Chromosome duplication
Sister chromatids
Chromosome distribution to daughter cells
Figure 8.4C

12. 8.5 The cell cycle multiplies cells
The cell cycle consists of two major phases
INTERPHASE
S (DNA synthesis) G1 G2
Cytokinesis
Mitosis
MITOTIC PHASE (M)
Figure 8.5

13. During interphase
Chromosomes duplicate and new cell organelles are made
During the mitotic phase
Duplicated chromosomes are evenly distributed into two daughter nuclei

14. 8.6 Cell division is a continuum of changes
In mitosis, after the chromosomes coil up / condense
A mitotic spindle moves them to the middle of the cell

15. The sister chromatids then separate
And move to opposite poles of the cell, where two nuclei form

16. Cytokinesis, in which the cell divides in two (division of cytoplasm)

17. The stages of cell division
LM 250
INTERPHASE
PROPHASE
Late PROPHASE
Centrosomes (with centriole pairs)
Fragments of nuclear envelope
Early mitotic spindle
Centrosome
Chromatin
Nucleolus
Nuclear envelope
Plasma membrane
Chromosome, consisting ot two sister chromatids
Centromere
Spindle fibres

18. TELOPHASE AND CYTOKINESIS
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Spindle
Metaphase plate
Daughter chromosomes
Nuclear envelope forming
Cleavage furrow
Nucleolus forming
Figure 8.6 (Part 2)

19. 8.7 Cytokinesis differs for plant and animal cells
In animals
Cytokinesis occurs by a constriction of the cell (cleavage)
Cleavage furrow
SEM 140
Daughter cells
Cleavage begins
Contracting ring of microfilaments
Figure 8.7A

20. A new cell wall form splits the cell in two
In plants
A new cell wall form splits the cell in two
TEM 7,500
Cell plate forming
Wall of parent cell
Daughter nucleus
Cell wall
New cell wall
Vesicles containing cell wall material
Cell plate
Daughter cells
Figure 8.7B

21. 8.10 Growing out of control, cancer cells produces malignant tumors
CONNECTION
8.10 Growing out of control, cancer cells produces malignant tumors
Cancer cells
divide excessively to form masses called tumors

22. Can invade other tissues
Malignant tumors
Can invade other tissues
Tumor
Glandular tissue
A tumor grows from a single cancer cell.
Cancer cells invade neighboring tissue.
Cancer cells spread through lymph and blood vessels to other parts of the body.
Lymph vessels
Blood vessel
Figure 8.10

23. Radiation and chemotherapy
Are effective as cancer treatments because they interfere with cell division

24. 8.11 Review of the functions of mitosis: Growth, cell replacement, and asexual reproduction
When the cell cycle operates normally, mitotic cell division functions in
Growth
LM 500
Figure 8.11A

25. Replacement of damaged or lost cells
LM 700
Figure 8.11B

26. Asexual reproduction
LM 10
Figure 8.11C

27. MEIOSIS AND CROSSING OVER
8.12 Chromosomes are matched in homologous pairs
The somatic (body) cells of each species
Contain a specific number of chromosomes
For example human cells have 46
Making up 23 pairs of homologous chromosomes

28. The chromosomes of a homologous pair
Carry genes for the same characteristics at the same place, or locus
Chromosomes
Centromere
Sister chromatids
Figure 8.12

29. 8.13 Gametes have a single set of chromosomes
Cells with two sets of chromosomes
Are said to be diploid
Gametes, eggs and sperm, are haploid
With a single set of chromosomes

30. Multicellular diploid adults (2n = 46)
Sexual life cycles
Involve the alternation of haploid and diploid stages
Mitosis and development
Multicellular diploid adults (2n = 46)
Diploid zygote (2n = 46) 2n
Meiosis
Fertilization
Egg cell
Sperm cell n
Haploid gametes (n = 23)
Figure 8.13

31. 8.14 Meiosis reduces the chromosome number from diploid to haploid
Meiosis, like mitosis
Is preceded by chromosome duplication
But in meiosis
The cell divides twice to form four daughter cells

32. The first division, meiosis I
Starts with synapsis, the pairing of homologous chromosomes
Meiosis I separates each homologous pair
And produce two daughter cells, each with one set of chromosomes

33. Meiosis II is essentially the same as mitosis
The sister chromatids of each chromosome separate
The result is a total of four haploid cells

34. MEIOSIS I: Homologous chromosomes separate
The stages of meiosis
MEIOSIS I: Homologous chromosomes separate
INTERPHASE PROPHASE I METAPHASE I ANAPHASE I
Centrosomes (with centriole pairs)
Sites of crossing over
Spindle
Microtubules attached to kinetochore
Metaphase plate
Sister chromatids remain attached
Nuclear envelope
Chromatin
Sister chromatids
Tetrad
Centromere
Homologous chromosomes separate
Figure 8.14 (Part 1)

35. MEIOSIS II: Sister chromatids separate
PROPHASE II METAPHASE II ANAPHASE II
TELOPHASE I AND CYTOKINESIS
TELOPHASE II AND CYTOKINESIS
Cleavage furrow
Haploid daughter cells forming
Sister chromatids separate
MEIOSIS II: Sister chromatids separate
Figure 8.14 (Part 2)

36. 8.15 Review: A comparison of mitosis and meiosis
Parent cell (before chromosome replication)
Chromosome replication
Chromosomes align at the metaphase plate
Tetrads align at the metaphase plate
Sister chromatids separate during anaphase
Homologous chromosomes separate during anaphase I; sister chromatids remain together
No further chromosomal replication; sister chromatids
separate during anaphase II
Prophase
Metaphase
Anaphase Telophase
Duplicated chromosome (two sister chromatids)
Daughter cells of mitosis 2n
Daughter cells of meiosis I n
2n = 4
Tetrad formed by synapsis of homologous chromosomes
Meiosis i
Meiosis ii
Prophase I
Metaphase I
Anaphase I Telophase I
Haploid n = 2
Daughter cells of meiosis II
Figure 8.15

37. 8.16 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring
Each chromosome of a homologous pair
Differs at many points from the other member of the pair

38. Two equally probable arrangements of chromosomes at metaphase I
Random arrangements of chromosome pairs at metaphase I of meiosis
Lead to many different combinations of chromosomes in eggs and sperm
Combination 1
Combination 2
Combination 3
Combination 4
Gametes
Metaphase II
Two equally probable arrangements of chromosomes at metaphase I
Possibility 1
Possibility 2
Figure 8.16

39. Random fertilization of eggs by sperm
Greatly increases this variation

40. 8.17 Homologous chromosomes carry different versions of genes
The differences between homologous chromosomes
Are based on the fact that they can bear different versions of a gene at corresponding loci
Tetrad in parent cell (homologous pair of duplicated chromosomes) e c E C
White
Pink
Meiosis
Black
Brown
Chromosomes of
the four gametes
Eye-color genes
Coat-color genes
Brown coat (C); black eyes (E)
White coat (C); pink eyes (e)
Figure 8.17A

41. 8.18 Crossing over further increases genetic variability
Genetic recombination
Which results from crossing over during prophase I of meiosis, increases variation still further
Chiasma
Tetrad
Centromere
TEM 2,200
Figure 8.18A

42. Tetrad (homologous pair of chromosomes in synapsis)
How crossing over leads to genetic variation
Coat-color genes
Eye-color genes C E
Tetrad (homologous pair of chromosomes in synapsis) c e
Breakage of homologous chromatids 1 C E c e
Joining of homologous chromatids 2 C E
Chiasma c e 3
Separation of homologous chromosomes at anaphase I C E C e c E c e 4
Separation of chromatids at anaphase II and completion of meiosis C E
Parental type of chromosome C e
Recombinant chromosome c E
Recombinant chromosome c e
Parental type of chromosome
Figure 8.18B
Gametes of four genetic types

43. New combination of genes in recombinant chromosomes

44. ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE
8.19 A karyotype is a photographic inventory of an individual’s chromosomes
A karyotype
Is an ordered arrangement of a cell’s chromosomes

45. Preparation of a karyotype from a blood sample
Blood culture
Fluid
Centrifuge
Packed red and white blood cells
Hypotonic solution
Fixative
White blood cells
Stain
Centromere
Pair of homologous chromosomes
Sister chromosomes
2,600X
A blood culture is centrifuged to separate the blood cells from the culture fluid. 1
The fluid is discarded, and a hypotonic solution is mixed with the cells. This makes the red blood cells burst. The white blood cells swell but do not burst, and their chromosomes spread out. 2
Another centrifugation step separates the swollen white blood cells. The fluid containing the remnants of the red blood cells is poured off. A fixative (preservative) is mixed with the white blood cells. A drop of the cell suspension is spread on a microscope slide, dried, and stained. 3
The slide is viewed with a microscope equipped with a digital camera. A photograph of the chromosomes is entered into a computer, which electronically arranges them by size and shape. 4
The resulting display is the karyotype. The 46 chromosomes here include 22 pair of autosomes and 2 sex chromosomes, X and Y. Although difficult to discern in the karyotype, each of the chromosomes consists of two sister chromatids lying very close together (see diagram). 5
Figure 8.19

46. 8.20 An extra copy of chromosome 21 causes Down syndrome
CONNECTION
8.20 An extra copy of chromosome 21 causes Down syndrome
A person may have an abnormal number of chromosomes
Which causes problems

47. Down syndrome is caused by trisomy 21 An extra copy of chromosome 21
5,000
Figure 8.20A
Figure 8.20B

48. Infants with Down syndrome (per 1,000 births)
The chance of having a Down syndrome child
Goes up with maternal age
Age of mother 45 50 35 30 25 40 20 90 10 60 70 80
Infants with Down syndrome (per 1,000 births)
Figure 8.20C

49. 8.21 Accidents during meiosis can alter chromosome number
Abnormal chromosome count is a result of nondisjunction
The failure of homologous pairs to separate during meiosis I
The failure of sister chromatids to separate during meiosis II

50. Nondisjunction in meiosis I
Normal meiosis II
Gametes
n + 1
n 1
Number of chromosomes
Nondisjunction in meiosis II
Normal meiosis I
n -1 n
Number of chromosomes
Figure 8.21B
Figure 8.21A

51. Fertilization after nondisjunction in the mother
Sperm cell
Egg cell
n (normal)
n + 1
Zygote
2n + 1
Figure 8.21C

52. CONNECTION
8.22 Abnormal numbers of sex chromosomes do not usually affect survival
Nondisjunction can also produce gametes with extra or missing sex chromosomes
Leading to varying degrees of malfunction in humans but not usually affecting survival
Figure 8.22A
Poor beard
growth
Breast
Development
Under-developed
testes
Figure 8.22B
Characteristic facial
features
Web of
skin
Constriction
of aorta
Poor breast
development
Under developed
ovaries

53. Human sex chromosome abnormalities

54. CONNECTION
8.23 Alterations of chromosome structure can cause birth defects and cancer
Chromosome breakage can lead to rearrangements
That can produce genetic disorders or, if the changes occur in somatic cells, cancer

55. Deletions, duplications, inversions, and translocations
Reciprocal translocation
Nonhomologous chromosomes
Deletion
Duplication
Inversion
Homologous chromosomes
Figure 8.23B
“Philadelphia chromosome”
Chromosome 9
Chromosome 22
Reciprocal translocation
Activated cancer-causing gene
Figure 8.23C
Figure 8.23A