CELL DIVISION

1
CELL DIVISION MITOSIS Reproducing the
nucleus of a somatic cell. MEIOSIS
Producing sex cells (gametes). CYTOKINESIS
Division of cytoplasm and organelles.
2

• MITOSIS MEIOSIS, cont.
• Both mitosis and meiosis consist of a sequence
  of phases
• interphase (preparation for division)
• prophase
• metaphase
• anaphase
• telophase

3

• MITOSIS MEIOSIS, cont.
• Result of Mitosis
• formation of two daughter nuclei
• have the same chromosome number as original
  (parent) cell

4

• MITOSIS MEIOSIS, cont.
• Result of Meiosis
• formation of 1 to 4 daughter nuclei
• have half the chromosome number as original
  (parent) cell
• Concludes with cytokinesis
• division of the cytoplasm and organelles

5
I. MITOSIS A. Terminology 1.
Chromatin 2. Chromosome 3. Diploid (46 or
2N in humans) 4. Haploid (23 or N in
humans) 5. Homologous chromosomes 6.
Somatic cells
6

• MITOSIS, cont.
• B. PHASES arbitrarily assigned
• 1. INTERPHASE
• a. NO division. Cell appears to be
  resting
• b. the metabolic phase of the
  cell

7
Interphase, continued c. Chromatin
visible d. Nucleus, nuclear membrane, nucleolus
visible e. Centrioles located at
poles f. Longest phase 1. 96 of the
cells life cycle 2. average of 23/24 hours
8
Interphase of Mitosis
9
MITOSIS, cont. 2. Prophase a. Centrioles
move to opposite poles of cell b.
Chromatin condenses into chromosomes c.
Nucleoli disappear d. Spindle apparatus is
organized
10
Late Prophase of Mitosis
11
MITOSIS, cont. Prophase e. Toward end
of phase, nuclear membrane dissipates f.
Phase ends as spindle fibers attach to
centromeres g. Each chromosome now consists
of two chromatids
12
Chromosome at Metaphase
A single metaphase chromosome with two chromatids
13
MITOSIS, cont. 3. Metaphase a.
Chromosomes arranged around equatorial
plate b. Single file c. Two spindle
fibers attached at each centromere
14
MITOSIS, cont. Metaphase d. A relatively
short phase e. Chromosomes easily counted
(KARYOTYPE) f. Phase ends as chromatids
separate g. Centromere splits as DNA
replication is completed
15
Metaphase of Mitosis
16

• MITOSIS, cont.
• 4. ANAPHASE
• a. Begins as chromatids separate
• b. Spindles move chromosomes to opposite
  poles
• c. Polar spindles elongate cells
• d. Phase ends when chromosomes have
  arrived at poles

17
Anaphase of Mitosis
18
MITOSIS, cont. 5. Telophase a.
Reverse of prophase b. Identical sister
chromosomes have arrived at opposite
poles c. Nuclear membrane reassembles d.
Spindle apparatus dissipates e. Nucleolus
reassembles
19
MITOSIS, cont. Telophase f. Chromosomes
relax ? chromatin g. Centrioles replicate h.
Each chromosome consists of a single
complete strand of DNA i. Phase ends when
nuclear membrane is completely
reassembled
20
Telophase of Mitosis
21

• MITOSIS, cont.
• C. CYTOKINESIS
• 1. Begins during anaphase
• 2. Completed during telophase
• 3. Result two daughter cells
• a. Genetically identical to parent cell
• b. Contain 1/2 the cytoplasm, organelles

22
Mitosis
An overview of Mitosis showing all stages
23

• II. MEIOSIS
• A special case of mitosis
• Occurs during maturation of sex cells (gametes)
  
• Result daughter nuclei receive one half the
  number of chromosomes of somatic cells
• Makes sexual reproduction possible

24
II. MEIOSIS, cont. A. Terminology 1.
Haploid having a single set of
chromosomes per
individual or cell (N) 2.
Diploid having two full sets of
chromosomes per individual or
cell (2N)
25
II. MEIOSIS, cont. Diploid a.
Usually find sexual reproduction in diploid
organisms b. Provides enormous adaptive
advantages 1. allows for population
variations 2. Increases chances for survival
26
II. MEIOSIS, cont. Terminology 3. Homologous
chromosomes a. Chromosomes that
pair during meiosis b. Have the
same morphology c. Contain genes governing
the same characteristics
27
MEIOSIS, cont. Terminology 4. Allele one of
the two or more alternate forms of a gene
a. dominant, recessive, co-dominant b.
examples B Brown hair (dominant) b
blonde hair (recessive) c. Different alleles
arise by mutations
28
MEIOSIS, cont. Terminology 5. Gene a.
sequence of DNA nucleotides b. unit of heredity
transmitted in the chromosome 6.
Chromosome sequence of genes
29
II. MEIOSIS, cont. Terminology

• 7. One gene One enzyme theory
• A gene is that part of a DNA molecule responsible
  for the synthesis of one enzyme (polypeptide)

30
II. MEIOSIS, cont.

• B. Phases of Meiosis
• 1. Two sets of events
• 2. Same names as mitosis
• 3. Must indicate phase I or II I
  Reductional Division II Equational Division

31
II. MEIOSIS, cont.

• C. Reductional Division
• 1. Interphase I Like mitosis
• 2. Prophase I
• a. Long, complex
• b. Three subdivisions

32
II. MEIOSIS, cont. Prophase I

1. Early like mitosis 2. Middle
important a. homologs pair b. crossing over
occurs c. exchange of genetic info d.
called tetrads 3. Late like mitosis
33
Prophase I of Meiosis
34
II. MEIOSIS, cont.

• 3. Metaphase I
• a. Similar to mitosis
• b. Homologous pairs align
• c. One spindle fiber/centromere
• d. Ends as one of each pair is pulled
  to opposite poles
• e. NO DNA replication!!

35
II. MEIOSIS, cont.

• 4. Anaphase I
• a. Similar to mitosis
• b. Members of homologous pairs move to
  poles
• c. Moved by spindle fibers

36
Anaphase II of Meiosis
37
II. MEIOSIS, cont.

• 5. Telophase I
• a. Nuclear membrane reorganizes
• b. Chromosomes relax
• 6. Cytokinesis may not occur

38
Telophase I of Meiosis
39
II. MEIOSIS, cont.

• 7. End result
• a. Nuclei are haploid (N)
• b. Chromosome number is reduced by
  one-half

40
(No Transcript)
41
II. MEIOSIS, cont.

• D. Equational Division
• 1. Interphase II
• a. NO DNA replication!!
• b. Coffee break for nuclei
• c. May not occur

42
Interphase II of Meiosis
43
II. MEIOSIS, cont.

• 2. Prophase II
• a. Chromosomes condense
• b. Spindle apparatus forms
• c. Two fibers/centromere
• d. Membrane dissipates e. Like mitosis

44
II. MEIOSIS, cont.

• 3. Metaphase II
• a. Like mitosis
• b. Chromosomes on equator
• c. Single file
• d. Ends with centromere replication

45
Metaphase II of Meiosis
46
II. MEIOSIS, cont.

• 4. Anaphase II
• a. Centromeres replicate
• b. Chromatids pulled to opposite poles

47
Anaphase II of Meiosis
48
II. MEIOSIS, cont.

• 5. Telophase II
• a. Nuclear membranes
• reorganize
• b. Nucleolus reorganizes
• c. Chromosomes relax
• d. Centrioles replicate
• e. Like mitosis

49
Telophase II of Meiosis
50
(No Transcript)
51
II. MEIOSIS, cont.

• 5. Cytokinesis occurs
• 6. Result
• a. Females unequal division
  of cytoplasm
• -one ovum, 3 polar bodies
• b. Males equal division of
  cytoplasm
• -four spermatozoa

52
Telophase II of Meiosis Four new cells
53
II. MEIOSIS, cont.

• 7. Cells produced are
• a. Different from parent cell
• b. Different from each other
• c. Haploid

54
Spermatogenesis
Spermatogenesis results in four spermatozoa
55
Oogenesis
Oogenesis results in one Ovum and two or three
polar bodies