The Cell, Chromosome Structure, Cell Division, Mitosis, Meiosis, Life Cycles (terminal, initial, intermediary)

1. The Chromosomal
Basis of Heredity
Lecture 2
Bio 106

2. TOPICS
A. The Cell
B. The Chromosome Structure
C. Cell Division
1. Mitosis 2. Meiosis
D. Life Cycles
1. Terminal or Gametic Meiosis
2. Initial or Zygotic Meiosis
3. Intermediary or Sporic Meiosis

3. THE CELL

4. The Chromosome Structure

6. Components of a
Nucleosome :
Histone octomer: H2A, H2B,
H3, H4 (2 copies each)
146 bp of superhelical DNA

8. PARTS OF THE CHROMOSOME

13. CELL CYCLE

15. CELL DIVISION

16. ASPECT/FEATURE MITOSIS MEIOSIS
Number of
divisions
1 2
Number of cells
produced per
division
2 4
Type of cells
produced
Diploid (2N) Haploid (N)
Genetically
identical to
parent cell
Different from
parent cell;
varied
Type of cells
involved
Somatic cells Sex cells

17. MITOSIS

18. MITOSIS
- nuclear division of a cell
which produces two
daughter nuclei that are
genetically identical to
the parent nucleus.
- cytoplasmic division
usually follows nuclear
division.

19. MITOSIS
P
R
O
P
H
A
S
E
Chromosomes become more coiled
and thicker, the 2 sister chromatids
being connected by their
CENTROMERES.
Nucleolus disappears towards
the later part.
The 2 pairs of centrioles move apart
and spindle fibers start to form
between them.
Nuclear
envelope
Condensed
chromosomes
Mitotic spindle
Separating centrosomes
microtubules
Centrosome with 2 centrioles

20. MITOSIS
P
R
O
P
H
A
S
E Plant cell
Animal cell

21. MITOSISP
R
O
M
E
T
A
P
H
A
S
E
Breakdown of nuclear envelope
Kinetochore MTs attach to
kinetochores
Polar MTs push against each
other, moving centrosomes apart

22. MITOSIS
M
E
T
A
P
H
A
S
E
Centrosomes now at opposite
poles of the cell.
Chromosomes, now maximally condensed , are
lined up at the metaphase plate (equatorial plate).
They are held in place by spindle fibers coming
from the centrosomes (kinetochore MTs).
centrosome
Kinetochore
MT
Polar MT
Astral MT
Metaphase plate

24. MITOSIS
M
E
T
A
P
H
A
S
E
Plant cell
Animal cell

25. MITOSIS
A
N
A
P
H
A
S
E
Separation of sister chromatids
and their migration to opposite
poles
At the end of this stage, a
complete set of chromosomes has
assembled at each pole of the cell.
Single-strand daughter
chromosomes
Increasing
separation
of spindle
poles

26. MITOSIS
A
N
A
P
H
A
S
E
Plant cell
Animal cell

27. MITOSIS
T
E
L
O
P
H
A
S
E
Chromosomes
assemble in sets at
the 2 poles. They
uncoil and eventually
look like they did at
interphase. Nuclear envelope
reforms around
each set of
chromosomes.
Spindle fibers
disappear.
Nucleolus
reforms.
Nuclear division by mitosis is
now complete.

28. MITOSIS
T
E
L
O
P
H
A
S
E
Plant cell
Animal cell

29. MITOSIS
C
Y
T
O
K
I
N
E
S
I
S
Animal cytokinesis
Plant cytokinesis
In animal
cells, a
CLEAVAGE
FURROW
forms.
In plant cells, a
CELL PLATE forms.
centrosome
Complete nuclear
envelope

30. MITOSIS

31. No variation in chromosome number
No genetic variation
Formation of 2 identical diploid
daughter cells
Consequences of MITOSIS:

32. Why is MITOSIS important?
Regeneration
Growth
Cell replacement
Vegetative
reproduction

33. MEIOSIS
- two successive
divisions of a diploid (2N)
eukaryotic cell of a
sexually reproducing
organism that result in
four haploid (N) progeny
cells, each with half of
the genetic material of
the original cell.

34. MEIOSIS

36. 1
2
LEPTOTENE
ZYGOTENE
(synapsis)

37. 3
(Crossing over)
PACHYTENE
Formation of TETRAD / BIVALENT

39. 4
DIPLOTENE
5
DIAKINESIS

40. PROGRESSION FROM INTERPHASE to
PROPHASE I

41. Alignment of bivalents/tetrads
at the metaphase plate

42. Separation of bivalents/tetrads
and movement of double-strand
chromosomes to opposite poles

43. The 2 sets of chromosomes
complete their migration to
opposite poles.
Nuclear envelope reforms around
each chromosome set.
Cytoplasm divides.

44. 44

46. 46

51. 51

52. How meiosis generates GENETIC
VARIABILITY:
the exchange of genetic material between
homologous chromosomes during Meiosis I
the random alignment and orientation of
maternal and paternal chromosomes in
Meiosis I
the random alignment of the sister
chromatids at Meiosis II

53. MEIOSIS:
Prophase I
3
(Crossing over)
PACHYTENE
Formation of TETRAD / BIVALENT

54. LIFE CYCLES: 3 major kinds
Terminal or gametic meiosis

55. Terminal or gametic
Ex: animals
Only one multicellular stage:
diploid (2n)

57. Initial or zygotic
Ex: most fungi & protists
Often a dominant, multicellular
haploid stage (n), transitory
diploid stage (2n)
Zygotic and gametic life cycles
are called HAPLOBIONTIC.

59. Intermediary or sporic
Alternation of generations: both haploid
(n) and diploid (2n) are multicellular.
has two mitosis events
(DIPLOBIONTIC)
Ex: algae and plants

61. moss