Chromosomes
Chromosome Formation
ChromosomesROD Shaped structure
made of DNA and Protein
Histone ProteinsHelp maintain shape
of the chromosome
Structure of a Chromosome
CENTROMERE
CHROMATID
CHROMATID
Homologous ChromosomesHumans have
AUTOSOMES
Humans Have 44
Autosomes
SEX CHROMOSOMES
Humans have 2
Male XY
Female XX
46 chromosomes
23 homologous pairs
CHROMOSOME NUMBER
2n Chromosomes
Honeybee (female) – 32 Adder’s Tongue Fern - 1262
Human - 46
Cat - 38
Common Frog - 26
Maize - 20
Does more chromosomes
bigger
Chromosome
number mean
doesanot
or more complicated
organism?
determine
complexity
of organism
DIPLOID CELLS VS.
HAPLOID CELLS
Diploid 2N=
Contains both
autosomes in a
homologous pair
Haploid 1N=
Contains 1 autosome of
homologous pair
Human Body Cells are
Diploid
Human sex cells are
Haploid
Egg and Sperm Cell
Contain 46
chromosomes and
23 pairs
Contain 23
Chromosomes and
no pairs
Mitosis vs. Meiosis
46
46
23
23
46
46
23
MITOSIS
23
23
MEIOSIS
23
HOMOLOGOUS
CHROMOSOMES
Cell Division
Eukaryotes vs. Prokaryotes
Prokaryotes vs. Eukaryotes
Characteristics
Prokaryotes
 Single celled organisms

No membrane bound nucleus or
organelles

Simple and smaller


Eukaryotes
 Make up multicellular
organisms
 Have membrane bound
organelles and nucleus
 Complex and Larger

Many chromosomes
Have a cell wall

DNA located in the nucleus
Few chromosomes

Chromosomes coil and
condense before cell division
Prokaryotic Cell Division
• Binary fission
• Division of prokaryotic cell into two offspring cells
Cell Division in Eukaryotes
Cell Division occurs in two stages

Mitosis/Meiosis
Division of the nucleus
Four stages (Prophase, Metaphase, Anaphase, Telophase)

Cytokinesis
Division of the cytoplasm

Prokaryotic vs Eukaryotic Cell
Division
Prokaryotes
 DNA is circular and attached to the
plasma membrane
 DNA does not wrap around
proteins to form chromosomes
before cell division
 Binary Fission(most cells)
 Cell membrane will develop
between the two copies of DNA
 Cell Doubles in size
 Cell membrane pinches off
 Cell Wall forms around new cell
membrane
Eukaryotes
Chromosomes coil and condense
before cell division
Consists of 2 Divisions
1)Division of the nucleus
 Mitosis – body cells(Diploid
Cells)
 Meiosis- sex cells (Haploid
cells)
2) Division of the Cytoplasm
 Cytokinesis
What is the same in Euk and
Prok cell division?
Create new cells
 Genetically identical
 DNA is copied before cell division
 Cytoplasm will divide

Eukaryotic Cell Division
Cell Cycle
CELL CYCLE- Repeating set of events
in the life of the cell
Interphase-longest stage in the cell cycle
G1 – Cell growth (cell grows to a mature size)
S – DNA is copied (double the amount of
DNA)
G2 – Growth and preparation for cell division
G0-Cells that do not divide will remain in G0
(occurs at the end of G1)
Cell division
Mitosis/Meiosis – Nucleus divides
Cytokinesis – Division of the cytoplasm
What triggers the cell to leave on phase
and move to the next?
Checkpoints = traffic signal
 Proteins regulate the process
Three main checkpoints
 G1 checkpoint(end of G1)
 G2 checkpoint (during G2)
 Mitosis checkpoint (toward
the end of mitosis)
Control of Cell Division
G1 checkpoint-Cell Growth Checkpoint
 Checks to see if the cell is healthy and has reached a
mature size
 Will determine if the cell will divide
G2 checkpoint-DNA synthesis checkpoint
 DNA repair enzymes check the results of DNA replication
Mitosis checkpoint If cell passes this checkpoint, the cell will exit Mitosis and
move into G1 of interphase
What happens if there is a mutation in one of these proteins?
Organelle Review
Centrosomes



Contain two centrioles
Made of microtubules
Acts as anchors in cell division
Plants centosomes do not contain centrioles
Mitotic Spindle fibers-Two Main types


Kinetochore Fibers- Attach from centriole to centromere
of chromosomes and assists in movement of
chromosomes
Polar Fibers – Extend from pole to pole and keep the
shape of the cell during cell division
Organelle Review
Nuclear envelope
• Double Phospholipid bilayer surrounding
nucleus
• Surrounds the DNA
Nucleolus
• Dense area where DNA is concentrated in the
nucleus
• Ribosomes (rRNA) is synthesized
MITOSIS



Division of the nucleus
Forms two identical daughter cells
Four phases
Where does it occur?
Somatic Cells (Body cells)
Why does it occur?
• Asexual reproduction
• Growth and development
• To replace old cells or dying cells
Prophase
• Chromatin coils and condenses into
chromosomes
• Nucleolus and nuclear membrane
break down and disappear
• Centrosomes appear and move to
opposite ends of the cell
• Spindle Fibers appear: Kinetochore
fibers extend from kinetochore of
each chromatid to centrosome.
Metaphase
Metaphase = Middle
 Kinetochore fibers move
chromosomes to center of
the cell
 All chromosomes line up
in a single file line
 46 chromosomes lined up
in the middle (Humans)
Anaphase

Anaphase
• Chromosomes separate at the
centromere and chromatids move
to opposite poles
• Chromatids are now considered
individual chromosomes
Telophase
• Chromosomes are on opposite sides of
the cell
• Centrioles disappear and Spindle fibers
disassemble and disappear
• Chromosomes unwind into less tightly
coiled chromatin
• Nuclear envelope forms around each
set of chromosomes
• Nucleolus forms in each of the newly
forming cells
Animation
CYTOKINESIS
Cytokinesis-the division of the cytoplasm
Animal cells:
Pinching inward of the cell membrane occurs.
Called Cleavage furrow
In plants

cell plate formation
Which stage?
Mitosis vs. Meiosis

Where do they occur?



Mitosis – in the body cells
Meiosis – in the germ cells
Why does it occur?

Mitosis
• Asexual reproduction
• Growth and development
• To replace old cells

Meiosis
• Formation of gametes (egg and sperm cells)
that will be used in sexual reproduction
Mitosis vs. Meiosis
46
46
23
23
46
46
23
MITOSIS
23
23
MEIOSIS
23
Meiosis




Also known as reduction division
Occurs in germ cells found in the ovaries and testes
Produces sex cells which are haploid
Occurs in two phases
 Meiosis I
• Reduces the number of chromosomes from diploid
to haploid
 Meiosis II
• Produces four haploid daughter cells
Meiosis I
Meiosis I
Prophase I
 DNA coils tightly into chromosomes
 Spindle fibers and centrosomes
appear
 Nucleolus and nuclear envelope
disassemble
 Synapsis =Pairing of homologous
chromosomes
 Tetrad =Pair of homologous
chromosomes twisted around each
other
 Crossing over may occur
 Genetic recombination
Meiosis I

Metaphase I
• Tetrads line up along midline
• Independent assortment occurs

Anaphase I
• Homologous chromosome pairs(Tetrads) are separated and
move to opposite poles (Independent assortment occurs)

Telophase I
• Chromosomes reach opposite ends of cell
• Spindle Fibers disappear
• In some cells the nuclear envelope will reappear
• Cytokinesis begins
Meiosis II
Meiosis II
Prophase II
 Spindle fibers form and attach to the centromere of the
double stranded chromosomes. (Nuclear envelope
will disappear if it was created)
Metaphase II
 Double stranded chromosomes are moved to the
midline of the dividing cell
Anaphase II
 Chromatids separate and move toward opposite poles
Telophase II
 Nuclear membrane forms and nucleolus reappears,
spindle fibers and centrosomes disappear, chromatin
uncoils into chromosomes
Cytokinesis II
Division of the cytoplasm occurs
resulting in four new cells
Each cell contains half the original
amount of chromosomes
Mitosis vs. Meiosis
Development of Gametes in
Animals
Spermatogenesis
 produces Sperm or
Spermatozoa
 produces four
Oogenesis
 Cytoplasm is divided unequally
 Produces one mature egg cell or Ova
 Polar bodies are the three other products of meiosis
and they will eventually degenerate.