Mitosis and Meiosis
SC.912.L.16.17 Compare and contrast mitosis and meiosis and
relate to the processes of sexual and asexual reproduction and
their consequences for genetic variation.
Cell Division
 Process by which new cells form from existing cells
 Types of cell division
The First is cell division in prokaryotes, such as bacteria
(Binary Fission).
2. Eukaryotes use the second kind of cell division to grow and
to repair their bodies (Mitosis).
3. The third type of cell division occurs in eukaryotes. This
form of cell division (Meiosis) produces the specialized
cells involved in reproduction.
1.
Prokaryotic Cell Division
 Prokaryotes reproduce by binary fission.
 Steps of binary fission (relatively simple)
The cell’s genetic information (DNA) is copied.
2. The cell then splits into two. Each cell receives a complete
copy of the genetic information.
This creates two new cells that are identical to the
parent cell.
Bacteria reproduce by binary fission.
1.
Eukaryotic Cell Division
To give each cell the necessary genetic information, the cell
most copy its chromosomes before it divides. Since
eukaryotic cells have multiple chromosomes, the process of
duplicating them is more complex than the copying of the
single chromosome in an prokaryotic cell.
Cell division is more complex in eukaryotic cells than in
prokaryotic cells.
The Cell Cycle
Continuous process in which cells
1. Grow
2. Make copies of their
chromosomes (DNA
replication)
3. Divide to form daughter cells.
The three main Phases are:
1. Interphase
2. Mitosis
3. Cytokinesis
Phases of the cell cycle
INTERPHASE
 The cell spends most of its life in interphase, growing and
preparing to divide.
MITOSIS
 The nucleus divides into two nuclei
CYTOKINESIS
 The cell membrane pinches in and the cytoplasm divides,
forming two cells
INTERPHASE The cell spends most of its life in interphase, growing and preparing
to divide. Interphase has three parts
G1 phase, S phase and G2 phase
G1 phase
(Cell growth)
S phase
(DNA replication)
G2 phase
(Preparation for Mitosis)
The cell grows and carries
out routine functions.
It takes nutrients and uses
them for energy
Growth
Repairs damaged organelles
The cell increases in size
•The cells chromosomes are
copied.
•The duplication of chromosomes
is critical to normal cell function.
If chromosomes are copied
incorrectly, the change, or
mutation, may affect the
organisms in some way.
•The cell prepares the nucleus to
divide.
•Produces extra organelles and
cytoplasm.
Mitosis The cell divides into two nuclei. Mitosis ensures that each new cell receives a
copy of each chromosomes.
Mitosis has four phases
Prophase
Methaphase
Anaphase
Telophase
• Chromatin condenses
to form the
chromosomes.
•Pairs of sister
chromatics are attached
at regions called
centromeres.
•The nuclear
membrane breaks down
•Centrioles separate
and travel to opposite
poles of the cell
•Spindle fibers form
and organized
themselves around the
centrioles and attach
themselves to the
centromeres.
•Chromosomes line up
along the middle of the
cell
•Each chromosome is
attached to a spindle
fiber at its centromere.
•The sister chromatids
are pulled apart by the
spindle fibers and begin
to move to opposite
poles of each cell.
•The chromosomes
reach opposite poles of
the cell and begin to
unravel
•The spindle fibers
break down.
•The nuclear
membranes reforms
around the
chromosomes at each
pole.
Phases of Mitosis
Cytokinesis
 Once mitosis is complete, the cell membrane pinches in and
the cytoplasm divides , forming two cells that are identical to
the parent cell.
The Cell Cycle and Cancer
In some cases a mutation can occur during the process, altering the
cell cycle and causing new cells to form much more rapidly
than normal. This leads to uncontrolled cell growth (cancer)
Some cancers, such as skin cancer and lung cancers, are caused
by mutations in body cells that affect the genes that control cell
division.
Most skin cancer is caused when ultraviolet (UV) radiation in sunlight
damages skin cells.
In most cases of lung cancer, genes are damaged by chemicals in
tobacco products.
Asbestos, radiation, and some air pollutants can also alter cells in ways
that lead to lung cancer
Asexual Reproduction
 The production of offspring by a single parent
 The offspring is genetically identical to the parent
Types of Asexual reproduction
Binary fission (for many single celled organisms like bacteria)
Budding (In many multicellular) Cell division involving mitosis. A
small bud grows off the parent organisms, this will eventually break
off and become an independent organism)
Many plants can reproduce from asexually from runners or other
parts
Sexual Reproduction
 Cells from two parents join to form a new
individual
 Offspring produced are genetically
different from parent.
 Sexual reproduction involves gametes, or sex
cells. Gametes are haploid (they have half the
number of chromosomes)
 Gametes form by Meiosis.
Meiosis
 Meiosis is a process of cell division that reduces the number
of chromosomes by half.
 When sex cells form the chromosomes are copied once. The nucleus
then divides twice.
 The four cells that result have half as many chromosomes as a
normal body cell
Stages of Meiosis
MEIOSIS I
Prohase I
Metaphase I
Anaphase I
TelophaseI
Cytokinesis I
MEIOSIS II
Prohase II
Metaphase II
Anaphase II
TelophaseI I
Cytokinesis II
MEIOSIS I
Prophase I
 Homologous chromosomes pair up (process called synapsis)
 Crossing-over can occur. During crossing over, part of a chromatid on
one chromosome breaks off and switches position with the matching
portion on a chromatid of the homologous chromosome.
 Crossing-over increases the number of possible genetic
combinations in the offspring
Metaphase I
 The homologous pair line up along the center of the cell in a
random fashion called independent assortment.
 Like crossing –over, independent assortment leads to genetic
variation.
Anaphase I
 Spindle fibers separate the paired homologous chromosomes and pull
toward the oppsosite ends of the cell.
Telophase I and Cytokinesis I
 The cell divides to produce two daughter cells, each with a complete set
of chromosomes.
MEIOSIS II
 The two daughter cells divide again, to form four haploid cells
 Each haploid cell has a unique set of chromosomes
SC.L16.17 Compare and Contrast
Mitosis and meiosis
Feature
Meiosis
Mitosis
Definition
A type of cellular reproduction in
which the number of
chromosomes are reduced by half.
A process of asexual reproduction
in which the cell divides in two
producing a replica, (the number
of chromosomes stays the same)
Function
Sexual reproduction
Cellular Reproduction & general
growth and repair of the body
Type of cell produced
Sex cell known as gametes
(egg and sperm)
Body cell (blood cells, epithelial,
muscle, nerve cells etc)
Type of Reproduction
Sexual
Asexual
Daughter cells are
Genetically
Different from parent cell
(shows genetic diversity)
Identical to parent cell
(exact replica of parent cell)
Continuation….
Feature
Meiosis
Mitosis
Crossing over
Yes, mixing of chromosomes can No, crossing over cannot occur
occur
Paring of homologous
chromosomes
Yes, homologous chromosomes
separate and produce 4 haploid
daughter cells.
No
Beginning cell
Diploid cell
Diploid cell
Number of cells produced
II
4
II
2
Number of chromosomes
Half the original cell
Same as original cell
End product
4 Haploid cells
2 diploid cells
(the cells show genetic diversity) (an exact replica of the parent
cell)
II
II
I
I
I
I
Similarities between mitosis and
meiosis
 Both are forms of cell division.
 Both begin with diploid cells.
 Both occur within the nucleus of the cell.
 Both go through the same steps known as
Prophase, Metaphase, Anaphase and Telophase.
 Both have in common cytokines is (The cytoplasm divides)
Mitosis and Meiosis
Comparing Methods of Reproduction
Asexual Reproduction
Sexual Reproduction
Advantages
Produce many organisms
quickly
Since offspring are
genetically diverse, they may
be able to survive in more
varied conditions.
Disadvantages
No genetic variation
A factor such a toxin in the
environment that harms one
offspring can harm all of
them
Needs to find a mate
Produces relatively few
offspring