Mitosis & Meiosis - Teacher Notes
This PPT was revised June 25, 2007.
This PPT accompanies the Mitosis and
Meiosis Foldable.
The teacher will discuss the slides;
students will listen but take no notes.
When you reach the Foldable sections
which are indicated by a heading that
says “Mitosis – 1. Definition”, etc.,
the students will begin to take notes by
filling in their foldable.
Mitosis/Meiosis
DNA REPLICATION
and
CELL DIVISION
And Auld Lang Syne
Every body cell in an organism
must have the same number of
chromosomes.
Human body cells have 46 (2n–
diploid) chromosomes.
If it doesn’t, the cell will not be
able to function properly.
And Auld Lang Syne
Before a cell divides, the number
of chromosomes (the DNA) must
double.
Then each new cell can receive
the correct number of
chromosomes (DNA).
And Auld Lang Syne
The DNA replicates - makes an
exact copy of itself.
Step 1
Step 2
Step 3
And Auld Lang Syne
Replicated Chromosome – when
DNA replicates itself, it also
replicates the chromosome so that
the number of chromosomes also
doubles
Chromatid - replicated
DNA/chromosome still held
together at the centromere
And Auld Lang Syne
DNA
replication
occurs
during
interphase in
the period
known as
G2
M
G2
G2
S
MITOSIS
Now that DNA has replicated,
Mitosis can begin.
The cell now has two identical sets
of DNA/chromosomes.
MITOSIS
Mitosis is when the nucleus
of the cell divides.
one nucleus
one cell
identical nucleii
identical DNA
two nucleii
two cells
MITOSIS
Parent Cell
DNA condenses
into chromosomes
Chromosomes align
on the equator
Chromosomes
separate
Two daughter cells
Mitosis
Mitosis
Mitosis
Cytokinesis
Cytokinesis is the division of the
cell.
Animal cells: Cleavage
(indention in cell
membrane)
Plant cells: Cell plate
formation occurs.
It’s all about chromosomes!
There are 46 in human body cells
The number of chromosomes
remain constant during Mitosis
46
46
46
MITOSIS – 1. Definition
Mitosis is when the nucleus
of the cell divides.
one nucleus
one cell
identical nucleii
identical DNA
two nucleii
two cells
MITOSIS – 2. Type of Rep.
Only one parent cell
Daughter cells identical to the
parent cell.
one nucleus
one cell
?
two nucleii
two cells
identical nucleii
identical DNA
Mitosis – 3. Advantages
offspring cells are exactly like the
parent cell
Speed
Replacement
Desirable Characteristics
Mitosis – 4. Why Divide?
to increase surface area
to repair damaged cells
to grow
Mitosis – 5. General
 human daughter cells from mitosis
have 46 chromosomes
46
46
46
Mitosis – 5. General
two daughter cells result from
mitosis
46
46
46
Mitosis – 5. General
Somatic cells – normal body
cells
Mitosis – 5. General
 daughter cells from mitosis have a
diploid chromosome number (2n)
46
46
46
MITOSIS - 6. Drawing
Mitosis results in two
diploid somatic
(body) cells exactly
like the parent cell.
MITOSIS
Parent Cell
DNA condenses
into chromosomes
Chromosomes align
on the equator
Chromosomes
separate
Two daughter cells
Mitosis Review
1. Is the beginning parent cell
diploid or haploid (2n or n)?
2. Are the daughter cells diploid or
haploid (2n or n)?
More Mitosis Review
3. How many
daughter cells are
produced?
4. Are the resulting
daughter cells different
from the parent cell?
More Mitosis Review
5. Are the resulting daughter cells
different from each other?
6. How many chromosomes are in
a human parent cell?
7. How many chromosomes are in a
human daughter cell from mitosis?
More Mitosis Review
8.What types of cells are
produced by mitosis?
9. Why (when) does a cell go
through mitosis?
What is Meiosis?
Meiosis is the formation of
gametes (egg or sperm) with a
haploid chromosome number,
Fertilized Egg Cell
What is Meiosis?
The fertilized egg (zygote)
produced by the sperm uniting
with the egg then undergoes
mitotic division to make the baby.
Fertilized Egg Cell
Cell Differentiation
Nerve
Cells
Muscle
Cells
Blood
Cells
Skin
Cells
Stem Cells
New individuals arise from zygote stem
cells through cellular differentiation
Why Meiosis?
The gametes must have only half
the necessary chromosome number
for a species
23
When two gametes
unite, the resulting cell
must have the exact
chromosome number for
that species.
23
46
Paternal
Homologs
MEIOSIS
Meiosis has two divisions
 Division 1,
immediately
followed by
Division II
Two
Daughter
Cells
2nd Division of Mitosis
1st Division of Mitosis
Maternal
Homologs
Four
Daughter
Cells
Meiosis
Meiosis begins with a
diploid parent cell
Meiosis ends
with four haploid
daughter cells
Meiosis
Meiosis
Meiosis
Meiosis
Meiosis
What differences can be seen with
meiosis at this point?
Meiosis
Meiosis
Meiosis
Meiosis
What differences can be seen with
meiosis at this point?
Meiosis Diversity
Meiosis results in gamete cells unlike
the parent cell.
Gamete cells have only half the
chromosome number.
Each of the four gamete haploid cells
have a different mix of chromosomes.
Meiosis Diversity
Additional diversity can occur because
of crossing over.
Crossing causes parts of one
chromosome to trade with another
like chromosome..
Certain traits “remix”.
Crossing Over
What is happening?
a A
b B
c C
a a A A
b b B B
c c C C
a a A A
b b B B
a a A A
b b B B
c C c C
c C c C
How does this affect
the individual
(offspring)?
a
b
a
b
A
B
A
B
c
C
c
C
Crossing Over
Click the link for a crossing over
animation.
http://www.tokyomed.ac.jp/genet/anm/mimov.gif
Meiosis – 1. Definition
Meiosis is the formation of
gametes (egg or sperm) with a
haploid (n) chromosome number.
Fertilized Egg Cell
Meiosis – 2. Type of Rep.
Produces gamete (sex) cells.
Fertilization: two gametes unite forming
a fertilized egg called a zygote
Fertilized Egg Cell
?
Meiosis – 3. Advantages
Meiosis produces haploid
daughter cells unlike the parent
cell and unlike each other.
Meiosis provides
diversity in a species.
Meiosis – 4. Why divide?
Meiosis produces cells with only half
the required chromosome number
for a species.
23
When two gametes
unite, the resulting cell
has the correct
chromosome number for
that species.
23
46
Meiosis – 5. General
Human gametes produced by
meiosis have 23 chromosomes
The cells have a haploid
number of
chromosomes.
23
23
Meiosis – 5. General
Four haploid cells result from
meiosis
Meiosis produces
23
gametes (sex cells).
23
23
23
MEIOSIS – 6. Drawing
Meiosis has two
divisions.
Meiosis results
in four haploid
cells unlike the
parent cell.
2nd Division of Mitosis
1st Division of Mitosis
Paternal
Homologs
Maternal
Homologs
MEIOSIS –
6. Drawing
Meiosis has two
Two
Daughter
Cells
divisions
Division I,
immediately
followed by
Division II
Four
Daughter
Cells
Meiosis Review
1. Is the beginning parent cell
diploid or haploid (2n or n)?
2. Are the resulting daughter cells
diploid or haploid (2n or n)?
More Meiosis Review
3. How many daughter cells are
produced?
4. Are the resulting
daughter cells
different from the
parent cell?
More Meiosis Review
5. Are the resulting daughter cells
different from each other?
6. What event causes additional
remixing of genes during meiosis?
More Meiosis Review
6. How many
chromosomes are in
a human parent cell?
7. How many
chromosomes are
in a human
meiosis daughter
cell?
MORE MEIOSIS REVIEW
8. What types of cells are
produced by meiosis?
Fertilized Egg Cell
Still More Meiosis Review
Meiosis produces egg & sperm
which unite to make a new
organism.
Let’s review
Mitosis & Meiosis
1st Division of Mitosis
cells are produced?
 Daughter cells haploid
or diploid?
 Daughter cells like or
unlike the parent cell?
 Produces gametes or
somatic cells?
 Has one division or
two divisions?
2nd Division of Mitosis
 How many daughter
MEIOSIS
MITOSIS
Comparing
Mitosis and
Meoisis
Mitosis vs. Meiosis
Event
Mitosis Meiosis
Produces 4 cells
Produces 2 cells
New cells identical
√
√
√
New cells different
New cells have the same
number of chromosomes as
parent
New cells have fewer
chromosomes than parent
√
√
√
Mitosis vs. Meiosis
Event
Beginning cells diploid (2n)
Beginning cells haploid (n)
Mitosis
√
Meiosis
√
Ending cells diploid (2n)
Ending cells haploid (n)
√
Produces egg and sperm
√
Produces body cells
√
√
TRY THIS!
Free Write
 On your own paper compare and contrast
mitosis and meiosis.
 You must continually write for 2 minutes.
Works Cited
 “Fertilization - sperm fertilizing egg”, (No Date).
Wikipedia.com, Retrieved June 20, 2006 from the
World Wide Web:
http://en.wikipedia.org/wiki/Image:Fertilisation.jpg,
Website Copyright Permission: This image is
copyrighted. However, the copyright holder has
irrevocably released all rights to it, allowing it to
be freely reproduced, distributed, transmitted,
used, modified, built upon, or otherwise exploited
in any way by anyone for any purpose,
commercial or non-commercial, with or without
attribution of the author, as if in the public domain.
 Biology Curriculum Writing Team. PISD