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Cellular Reproduction
Chapter 2:
pp. 32-35
Chapter 3:
pp. 49-56
Fat Cells
Chromosomes-
DNA tightly coiled
around proteins
Humans have 46
The Cell Cycle (figs. 2.14 & 2.17)
Interphase: 90% of time
1. First Growth (G1)
2. Synthesis Phase (S)
3. Second Growth (G2)

Prepare for Mitosis
G1
 Cell Grows Rapidly
 Length varies greatly depending on cell type



Liver cells enter G0 and may be there for yrs.
Bone marrow only in G1 for hrs.
Early cells in embryo skip this phase all together
S
 Cell’s DNA copied
 Each chromosome consists of 2 copies
(2 chromatids) joined together by a
centromere
 ~ 8-10 hrs.
G2
 More protein synthesis
 Membranes formed and stored in vesicles
near cell membrane to be used for daughter
cells
Cell Division
 Surface area to volume ratios

Surface area ÷ Volume =
 Cells must divide because Volume of cell
becomes greater than the Surface Area or the
ratio is too low.
 Big cells are inefficient
Nuclear Division
Skin Cells
Mitosis –(Fig 2.16)
In your book
 Occurs in
Somatic Cellsall cells but
sperm & egg
cells.
 Nucleus of cell
divides
Cellular
Cellular
Reproduction
Reproduction
•Begins with
division of
nucleus
Link!Mitosis
animation
Prophase
Aster- fasten centrioles to
cell membrane
 DNA coils up and thickens
and tightens the
chromosomes.

Enables them to separate easier
 Microtubules assemble to
form spindle fibers
 The nuclear envelope begins
to break down
 Nucleolus no longer visible
Metaphase
 Chromosomes move to
the middle of the cell and
line up along the equator.
 Spindle fibers link the
chromatids of each
chromosome to opposite
poles.
 Centrioles (Centrosome)
Anaphase
•Centromeres divide
•Chromatids (now
called chromosomes)
move toward opposite
poles
•Very brief phase
Telophase
 A nuclear envelope
forms around the
chromosomes at each
pole
 Chromosomes uncoil
 LAST step in mitosis
Cytokinesis
•Cytoplasm is divided in ½
•Organelles distributed to 2
daughter cells
•Microfilament contracts
like a drawstring
•Cell membrane encloses
each cell
Control of the Cell Cycle
 Groups of interacting proteins function at
times called checkpoints- ensure correct
replication of chromosomes
1.
2.
3.
DNA damage
-repair DNA
Apoptosis
-keep cell alive (survivins)
Spindle Assembly - oversees spindle construction
When do divisions stop?
 Telomeres



act as fuses
100s-1000s of nucleotides
50-200 used during mitosis
Mitosis stops

Cell may die or live long
Apoptosis
?’s 1-14
 Cell Death
 Rapidly dismantles cell into membrane
bound pieces that other cells (phagocytes)
can pick up
 Death receptor
 Mitosis and Apoptosis are synchronized

Except in Cancer
Meiosis: (Fig. 3.3)
In your book
Production of
sex cells
1/2 the number
of Chromosomes
Link!-video
Gametes-reproductive
cells
Definitions for Meiosis
 Occurs in germ cells- inherited sex cells (gametes)
 Homologous ChromosomesChromosomes that are similar
in size, shape and content

 Crossing OverPortions of one chromatid are
shared with a chromatid on
another (Homologous
Chromosome)

Tetrad
Definitions for Meiosis
 Haploid- containing one set of chromosomes

23 for humans (sex cells)
 Diploid- containing two sets of chromosomes
 Zygote- fertilized egg



46 chromosomes in humans
78 chromosomes in dogs
Some plants have thousands
Definitions for Meiosis
 Asexual Reproduction-a single parent passes
copies of all of its genes to each of its
offspring. (Clones)
 Sexual Reproduction-two parents, each
donating a haploid reproductive cell
Meiosis
 Two divisions

Reduction division (Meiosis 1)
 Reduces
chromosomes from 46 -23
 Separates Homologous Chromosomes

Equational division (Meiosis 2)
2
cells become 4 cells
 Separates sister chromatids
Prophase 1
 90% of meiosis
 The chromosomes. become
visible
 Nuclear envelope breaks down
 Homologs line up-Synapsis
 Crossing over- Homologous
chromosomes (homologs)
exchange parts
Metaphase 1:
 Pairs of homologous
chromosomes move to the
equator of the cell
 Independent Assortment
Random arrangement of
the members of homolog
pairs in metaphase
Anaphase 1:
 Homologous
chromosomes move to
opposite poles of cell
Telophase 1:
 Chromosomes gather at
the poles of the cell
 Cytoplasm divides
 Short Interphase after
Telophase 1
 NO REPLICATION!
Prophase 2:
 A new spindle forms
around the
chromosomes
Metaphase 2:
 Chromosomes line up
at the equator
Anaphase 2
 Centromeres divide.
 Chromatids are now
called chromosomes
 Chromosomes move to
opposite poles of the
cell.
Telophase 2:





Cells begin split
Cell membrane between cells
Four gametes are formed
4 HAPLOID gametes
All cells different
Comparison
of Mitosis
and Meiosis
Table 3.1!!
46 Chromosomes (Diploid)-23 pairs
?’s 14-20
Trisomy 21 or Downs Syndrome
Extra Chromosome
Compare Mitosis and Meiosis
1.
2.
3.
4.
5.
6.
7.
8.
Answer these on a clean sheet
of paper
What kind of cells?
# of nuclear divisions
Compare daughter cells and parent cells
Chromosome # after division
Do homologous chromosomes pair?
Does Crossing over occur
When do the centromeres divide?
When is each type of cell division used?
Comparison of Mitosis and Meiosis
Mitosis
KEY
1. Somatic Cells
2. 1 nuclear division
3. Daughter cells identical to
parent cells
4. Diploid (remain constant)
5. No pairing of homologous
Chromosomes
6. Crossing over rare
7. Centromeres divide at
Anaphase
8. Growth, repair, asexual repro
Meiosis
1. Germ Cells
2. 2 nuclear divisions
3. Daughter cells differ from parent
cells
4. Haploid (Halved)
5. Pairing of homologous
Chromosomes
6. Crossing over
7. Centromeres Divide at Anaphase
2
8. Sexual repro., new gene
combinations arise