Cell Division Notes
Mitosis and Meiosis
Cell Cycle














Encompasses the time between the creation of a _______________________ and that cell’s division.
_____________________________: the splitting of one cell into two.
The process that makes _______________________ and ________________________ possible for any organism.
Each division different depended upon if the cell is eukaryotic or prokaryotic
Two major phases
1- Interphase: _______________________________________
Three phases:
G1 phase (Growth 1): ______________________________ – Cell organelles are formed within the cell.
S phase (Synthesis): DNA is ________________________________
G2 phase (Growth 2): Second period of cell growth, during which the ________________________ for the division.
Example: Some cells, including many nerve cells, are programmed never divide. These cells are said to be in G0 or
resting phase.
2- Mitosis: __________________________
Four phases of mitosis (__________________________________________________)
Cytokinesis: division of _________________________- and cell membrane
Cell Cycle Control


All of the cell cycle are controlled by__________________________________
There are three checkpoints
Checkpoints
Occurs at
Details
__________
The end of
the phase
If conditions are not suitable for replication,
the cell will not proceed to S phase but will instead
enter a resting phase G0
__________
__________



The end of
the phase
If conditions are not suitable, transition to the M phase will be delayed.
Between
metaphase
and
anaphase
stages of
mitosis
If the chromosomes are aligned properly and ready for division,
If DNA is damaged, cell division will be delayed to allow time for DNA repair
the cell will proceed from metaphase to anaphase, during which it will divide.
If the chromosome are not aligned properly, the anaphase stage will be delayed
Triggers at each checkpoint assess the cell’s readiness to proceed to the next stage.
Checkpoints makes sure proper number of _______________________ and type of chromosomes & organelles
Example: Malignant cancer are deadly, in part, because they undergo unregulated cell division, which enables them
to spread rapidly throughout the body. Scientists have discovered one reason behind this uncontrolled growth: a
defective p53 gene. Proteins produced by the p53 gene assess the cell’s DNA for damage at the G1 checkpoint. If the
DNA is intact, cell division proceeds. If the DNA is damaged, however, the p53 proteins halt cell division until the
DNA is repaired or the cell is destroyed. If the p53 gene itself has been damaged, as in the case of cells that are
cancerous the G1 checkpoint will fail and a malignant cancer cell may develop.
Other Cell Division Controls





_________________________________: When a certain density of cells is reached, growth of the cells will slow or
stop because there are not enough raw materials for the growth and survival of more cells.
Example: Cancer cells can lose this inhibition and grow out of control.
____________________________: Some cells will not divide if certain factors are absent.
_____________________________: is a protein that acccumlates during G1, S, G2, of the cell cycle
____________________________: is a protein that control other proteins through the addition of phosphate
groups.
Chromosomes








In eukaryotic cells, ________________ and associated ______________________are wrapped together in packages
called chromosomes.
DNA in eukaryotic cells is wrapped around the proteins to form a complex called______________________
Throughout the cell’s life, the chromatin becomes is loosely packed within the ________________________.
Chromatin can ____________________ been seen by humans.
Think a rubber band ball.
During cell division, however, the ___________________________ becomes highly condensed and folds up to form
condensed chromosomes. (This is when we can see it).
DNA is always _________________________, or copied before becoming condensed .
The X shape associated with chromosomes actually represents a ______________________chromosome consisting
of two identical sister __________________________ joined at the______________________________
Example: Prokaryotes do not have
chromosomes. Prokaryotic DNA exist in a
single loop

Chromosomes Number






Refers to the number of ____________________________ within each cell of an organism.
Most animals possess two nonidentical version of every chromosome. These are known
as___________________________________________.
Homologous chromosomes have the same size, shape, and function but may have slightly different versions of most
genes, the basic unit of __________________________________ information.
Cells with two sets of every chromosomes between their homologous chromosomes are
________________________ (2n), while cells with one set of every chromosome are haploid (1n)
Diploid: _________________________________ (Body) Cells
Haploid: ________________________ (Sex) Cells

Human Chromosome Number







Humans has __________ chromosomes or_______________ pairs
2n indicates _______________________
2n= 46 (2 sets of 23 chromosomes)
1n indicates_________________________
1n=23 (1 set of 23 chromosomes)
___________ and _________________ are haploid
The union of sperm and egg that occurs during ___________________________ restores the chromosomes number
of the resulting embryo to 2n = 46
Mitosis



Is the method of eukaryotic cell division that produces ____________________genetically identical cells.
All cells in an organism, except for sperm and eggs, are produced by the process of__________________.
Mitosis progresses along five stages: __________________________________________________________
Prophase




Duplicated chromosomes condense and become visible as distinct sister ____________________________.
Nuclear envelope ______________________
__________________________ move toward the poles of the cell.
The mitotic spindle, which is made of microtubules attaches to a specialized structure called the
__________________________, located at the centromere of each replicated chromosomes.

Metaphase


Replicated chromosomes align at the ___________________________, or metaphase plate, of the cell.
M&Ms (Metaphase Middle)

Anaphase


The sister chromatids separate and are moved toward opposite _________________________ of the cell by the
spindle.
As this happens, the cell begins to _____________________ toward the poles.

Telophase


Mitotic_______________________ breaks down.
______________________________ forms at each end of the cell, and the chromosomes within begin to unfold into
chromatin.

Cytokinesis




The cytoplasm and organelles are evenly divided between the two new cells during ________________________,
completing the process of cells division.
Plants and animals cells differ in cytokinesis
Plants, a ______________________ is formed as vesicles containing cell membrane materials fuse together along
the equator of the cell.
Animals, a ring of microfilaments contracts in the center of the elongated cell, producing a
_______________________________ that eventually pinches off the two cells.
Cell Cycle Diagram

Binary Fission






Occurs in prokaryotes because have a single double-stranded_______________________ of DNA.
Occurs in four steps
1. DNA is __________________________
2. Cell ____________________________ in size
3. _____________________________ grows into the center of the cell, between the two circles of DNA, dividing the
cell in two.
4. Two cell ___________________________, and a cell wall forms around each new cell.
Meiosis (“Me” like Sex (Cells))






The method of cell division that takes place in sexually reproducing organisms specifically for the creation of
__________________________– __________________ and ______________________ cells.
Production _____________________________________ cells, each genetically different
Meiosis requires ______________________ rounds of cell division
Meiosis I: Homologous pairs of each chromosome join and might exchange _______________________material.
The homologous chromosomes are pulled to opposite poles in the cell, at which point the cell separates, resulting in
two cells. Each cell contains half the chromosome number of the original diploid cell. Each chromosome remains in
the duplicated state and is made up of two sister _______________________________
Meiosis II: The second stage of meiosis follows similar steps as mitosis in the creation of ____________________
more cells. Chromosomes __________________________ replicate between Meiosis I and Meiosis II.
The result is _________________________ cells genetically different from one another.
Prophase I



The most important events in prophase I are synapsis and ________________________
__________________________________: occurs when the two homologous chromosomes condense and combine
to form complexes called tetrads
_________________ is the exchange of genetic material that takes place between these homologous chromosomes
along several junctions known as ____________________________________ (place where crossing over occurs)
Example:
Crossing Over

Metaphase I

The tetrads align along the metaphase___________________________ of the cell.
Anaphase I



The homologous chromosome of each tetrad and are pulled toward ______________________ of the cell by the
spindle.
The side of the cell toward which a homologous chromosome is pulled a random, depending only on the orientation
of the ___________________________.
The _____________________________________________ of chromosome for each cell is result of this random mix
of chromosomes derived from that organism’s parent
Telophase I




Identical to telophase in mitosis.
The cell continues to elongate, and the mitotic _________________________breaks down.
A new nuclear envelope forms at each end of the cell the chromosomes within unfold into
______________________
Example: Crossing over and the independent assortment of chromosomes during meiosis are two forces that help
to produce _________________________________ . By independent assortment alone, a single human can
produce more than 8 million genetically different gametes. When crossing over is also considered, the possible
number of genetically different is nearly limitless.
Cytokinesis I




__________________________________is very similar to mitosis divide cytoplasm and organelles.
Two genetically different ______________________________ cells have been produced.
Each chromosome is still in the duplicated state and is made up of two sister _______________________.
Because crossing over during prophase I, the sister chromatids are no longer identical.
Meiosis I Diagram
Meiosis II


Meiosis II occurs right after _______________________________
There is no ___________________________________ (therefore No DNA Replication)
Prophase II


_______________________________ condense within haploid cell condense, and the spindle attaches to the
kinetochore of each chromosome.
The ______________________________ breaks down and the centrosomes move toward the poles of the cell.
Metaphase II

Chromosomes align along the _______________________ of the metaphase plate
Anaphase II


The sister chromatids separate and are moved toward __________________________ of the cell by the spindle.
The cell begins to elongate toward the ________________________-
Telophase II


The cell continues to elongate and the mitotic spindle breaks down.
A ____________________ nuclear envelope forms at each end of the cell and the chromosomes within may unfold
into__________________________.
Cytokinesis II


The cytoplasm and organelles are divided between the two cells, completing the process of ___________________.
By the end of this stage, ___________________________ genetically ______________________cells have been
produced.
Sex Cells (Gametes)







Meiosis produces four genetically different haploid cells.
Males haploid cells are ______________________________
All four ___________________ can be used in _______________________reproduction.
Females haploid cells are 1__________________ and 3 polar bodies
Only the ___________________ can be used in sexual reproduction
The three polar bodies will be_______________________- back into the body.
Comparison Mitosis and Meiosis

Example: The process of meiosis results in four genetically different haploid cells. In animals, these haploid cells
develop into gametes, a sperm in males and an egg in females. _______________________________is the process
by which a sperm and egg fuse together. The resulting zygote is diploid, with half the chromosomes coming from the
mother and other half coming from the father. The processes of meiosis and fertilization both account for the
genetic variation found in animals of the same species. Meiosis is responsible for creating gametes whose genetic
material varies from that of the parent. Fertilization then combines the genetic material of the two parents to
produce the genetic material of the offspring
Life Cycle








____________________________________ is the sequence of events that make up the reproductive cycle of an
organisms.
______________________________________________: Plants sometimes exist as a diploid organism and other
times as a haploid cell.
Two haploid gametes combine to form a diploid ____________________________, which divides mitotically to
produce.
_________________________________: undergoes under meiosis to produce a haploid spore
_____________________________: Mitotic division leads to production of haploid multicellular organisms.
Produces haploid gametes, which form diploid __________________________
Alternation of Generation
Human Life Cycle




The only haploid cells present in this life cycle are gametes formed during __________________________.
Two haploid gametes combine during _______________________________ to produce a diploid zygote.
Mitotic division then leads to formation of the diploid __________________________ organisms.
Meiotic division later produces haploid ________________________.

Life Cycle of Fungi






Fungi are _________________________ organisms with the zygote being the only diploid form.
Like humans, the gametes for fungi are haploid (n), and fertilization yield a diploid zygote.
Instead of dividing by mitosis, the zygote divides by meiosis to form a ______________________ organisms.
Gametes are formed by ________________________, not meiosis—the organism is already haploid, before forming
the gametes.
We will discuss more about the life cycles as we get into the individual kingdoms.