human reproduction

1. Lecture 26/27
Human
Reproduction 1
1

2. CELL DIVISION
 There are 2 types of cell division depending on
whether the chromosome number in the cell is to
be
A) maintained constant or
B) halved.
2

3. STRUCTURE OF CHROMOSOMES
 In the nucleus of every living cell
there are thread-like structures
called chromosomes.
 Chromosomes are made up of
DNA (deoxyribo nucleic acid) and
proteins.
 DNA contains a set of instructions
to the cell.
 These instructions tell the cell what
proteins to make.
3

4. STRUCTURE OF CHROMOSOMES
DNA molecules are very long.
 A DNA molecule may contain instructions
for many different proteins.
 A section of a DNA molecule which gives
instructions to make any one kind of
protein is called a gene.
 Genes determine the characteristics of an
organism.
 All the cells in the body have the same
type of genes.
 But all the genes are not active in the cell.
4

5. Protein
DNA
Gene
Trait

6. HUMAN CELLS CONTAIN TWO OF
EACH KIND OF GENE
 Except for the sex cells all human
cells have 46 chromosomes.
 These 46 chromosomes can be
sorted into pairs.
 There are 23 kinds of human
chromosome.
 The two chromosomes of a
matching pair is called a
homologous set of chromosomes.
 Homologous chromosomes contain
the same kinds of genes in the
same places along their length.
6

7. 7
e.g. 23 chromosomes in haploid
2n = 46; n = 23
!
HUMAN CELLS CONTAIN TWO OF
EACH KIND OF GENE

8. HUMAN CELLS CONTAIN TWO OF
EACH KIND OF GENE
 Homologous chromosomes contain the
same kinds of genes in the same places
along their length.
 So you have two of each kind of gene.
 A cell containing two of each kind of
chromosomes is called a diploid cell, Eg:
somatic cells.
 A cell containing one of each kind of
chromosome is called a haploid cell, Eg:
gametes.
8

9. Meiosis KM 9
Chromosome numbers
All are even numbers –
diploid (2n) sets of
homologous
chromosomes!
Ploidy = number of
copies of each
chromosome.
Diploidy

10. MITOSIS
 Mitosis is a process that takes place
in the nucleus of a dividing cell
 results in the formation of two new
nuclei, each having the same
number (diploid number) of
chromosomes as the parent
nucleus.
 Before a cell divides the
chromosomes in the nucleus are
very difficult to see because they
are very long and thin.
10

11. 11
Cell Division
Demands
Coordination of DNA
Replication, Mitosis
and Cytokinesis
What’s so important
about cell division?

12. Mitosis –
1 2
3
4
5
Parent cell
Chromosomes copied
Copies separating 2 daughter cells
Cells split

13. Stages of mitosis
Interphase
 Before a cell divides the chromosomes in
the nucleus are very difficult to see
because they are very long and thin.
 Just before cell division, the DNA of each
chromosome replicates (form copies)
13
interphase

14. 14
1. Prophase
Chromosomes get
shorter and fatter
Stages of mitosis - Prophase

15. 15
 As chromosomes condense - each
chromosome seen as 2 identical
chromatids joined at the centromere.
Stages of mitosis - Prophase

16. 16
•Nuclear membrane breaks down
•The centrioles move to opposite ends of the
nucleus.
• Chromosomes then become attached to a
spindle (fibers that run from one pole to
another)/spindle apparatus forms
Stages of mitosis - Prophase

17. Stages of mitosis - Metaphase
2.Metaphase
 Next the chromosomes line up
along the center of the cell
(attached by their centromeres to
the spindle fibres)
17

18. 18

19. 3. Anaphase
Their two chromatids split apart and
move to opposite side of the cell
19
Stages of mitosis -Anaphase

20. 4. Telophase
 The chromatids (now also considered chromosomes)
arrive at the opposite ends of the cell, and new nuclear
membranes form (i.etwo nuclei forms)
 Telophase may lead to cytokinesis (cell division)
20
Stages of mitosis - Telophase

21.  The cell splits into two.
 Therefore in mitosis the
original cell (parent cell)
has now become 2
daughter cells:
 Identical to one another
 Identical to parent cell
 Have same (diploid)
number of chromosomes
as the parent cell
21
Stages of mitosis - Cytokinesis

22. 22
In Animal Cells, a Cleavage
Furrow Forms and Separates
Daughter Cells
Cleave furrow in a dividing frog cell.

23. 23

24. 24
The Plant Cell Wall Forces Cytokinesis to Play by Different Rules

25. 25

26. REMEMBER!
Interphase
Prophase
Metaphase
Anaphase
Telophase
IPMAT

27. 27

28. Name the stage
28

29. 29

30. 30

31. 31

32. REVIEW
32

33. 33

34. 34

35. 35

36. 36

37. 37

38. Activity
 Name phase of mitosis and sequence them
38

39. 39
Interphase Prophase
Metaphase Anaphase
Telophase Interphase
http://biology.nebrwesleyan.edu/benham/mitosis/

40. 40
Animal Cell
Reproduction
(Mitosis)
Plant Cell
Reproduction
(Mitosis)

41. 41

42. Mitosis
42

43. Plants
apical
meristem

44. Mitosis in an onion root
44

45. MEIOSIS
45

46. MEIOSIS
 Meiosis is a specialized type of cell
division that occurs in the formation of
gametes such as egg and sperm.
 Meiotic division will only occur in cells
associated with male or female sex
organs.
 Meiosis involves a reduction in the amount
of genetic material therefore it is also
known as reduction division.
 Meiosis comprises two successive nuclear
divisions with only one round of DNA
replication. 46

47. Meiosis -Summary
Parent cell – chromosome
pair
Chromosomes
copied
1st division - pairs split
2nd division – produces 4
gamete cells with ½ the
original no. of
chromosomes

48. Overview of meiosis: how meiosis reduces chromosome number
48

49. Stages of meiosis
 Before cell division the chromosomes in the
nucleus are very difficult to see because they are
very long and thin.
49

50. Meiosis I
1.In this step chromosomes appear, spindle fibers starts to
develop and the nuclear membrane breakdown.
50
Stages of meiosis - Meiosis I

51. 2.Unlike in mitosis the
chromosome pairs are
aligned on either side of
the equator
51
3. The spindle fibers
pull the homologous
pairs away from each
other and toward each
pole of the cell.
Stages of meiosis - Meiosis I

52. 4. A cleavage furrow forms at this point,
followed by cytokinesis, but the nuclear
membrane usually is not reformed and the
chromosomes do not disappear.
 At the end of this stage each daughter cell
has a single set of chromosomes, half the
total number in the original cell where the
chromosomes were present in pairs.
 While the original cell was diploid, the
daughter cells are now haploid. This is why
Meiosis I is often called reduction division.
52
Stages of meiosis - Meiosis I

53. 1. In Meosis II, A new set
of spindle fibers forms
and the chromosomes
begin to move toward
the equator of the cell
53
2. All the chromosomes in
the two cells align at
the equator of the cell
3.The chromatids are
pulled to opposite
poles
Stages of meiosis - Meiosis II

54. Stages of meiosis -
Meiosis II
4. Cell cleaves followed by
cytokinesis, nuclear membrane
forms
5.When Meiosis II is complete,
there will be a total of four
daughter cells, each with half
the total number of
chromosomes as the original
cell.
6. Result of meiosis: 4 gametes
containing only one set, the
haploid number of
chromosomes.
54
 Parent cell
Daughter cells

55. Meiosis KM 55

56. Meiosis – mouse testes
Parent cell
4 gametes
1st division
2nd division

57. Spermatogenesis
57
2n=46
human
sex cell
diploid (2n)
n=23
n=23
meiosis I
n=23
n=23
n=23
n=23
sperm
haploid (n)
meiosis II

58. A comparison of mitosis and meiosis
58

59. A comparison of mitosis and meiosis: summary
59

60. 60

61.  http://www.johnkyrk.com/mitosis.html
 http://highered.mcgraw-
hill.com/sites/0072437316/student_view0/cha
pter11/animations.html#
 http://www.quia.com/custom/3026main.html
61

62. The results of alternative arrangements of two homologous chromosome pairs on the
metaphase plate in meiosis I
62

63. The results of crossing over during meiosis
63

64. Fig. 1.22 Comparison of mitosis and meiosis in a diploid cell
64Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.
Crossing-over
Random assortment

65. Fig. 1.22 Comparison of mitosis and meiosis in a diploid cell (continued)
65Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

66. 66

67. Question:
 In terms of Independent Assortment -how many
different combinations of sperm could a human
male produce?
67

68. Answer
 Formula: 2n
 Human chromosomes: 2n = 46
n = 23
223 = ~8 million combinations
68

70. 70

71. Fig 2.4 The structure of a highly condensed, replicated chromosome.
© 2003 John Wiley and Sons Publishers

72. 72
DNA and Its Faithful Replication – The
Knit of Identity
Because DNA stores genetic information and is
faithfully replicated, information is passed largely
unaltered from cell-to-cell, generation-to-
generation.

73. 73

74. 74

75. 75
The Knit of Identity - Mitosis Precisely and Evenly Divides
Duplicated Chromosomes
Precisely dividing the duplicated chromosomes has the consequence of
providing each new cell with an identical and complete set of genetic
instructions.
interphase prophase metaphase

76. Mitosis Precisely and Evenly Divides Duplicated Chromosomes
Cytokinesis is the process of cell division and it is distinct and separable
from mitosis.

77. 77
Mitosis in Action
Blue
shows
DNA,
green
shows
spindle
fibers.

78. 78
 Each chromosome
seen as 2 identical
chromatids joined
at the centromere.
1. Prophase
Chromosomes
get shorter and
fatter
Chromosomes then
become attached
to a spindle
(fibers that run
from one pole to
another).
Stages of mitosis