Teacher Notes
 This PPT was revised November 19, 2008.
 This PPT is a companion PPT to Mitosis & Meiosis.
 There is a handout for this PPT.
Reproduction &
DNA Replication
How does DNA copy itself?
Why do cells divide?
to increase surface area
to repair damaged cells
to grow
to produce sex cells
Cell Reproduction
Cells reproduce either sexually or
asexually.
Bacteria
Asexual Reproduction
 Requires only one parent
 Binary Fission
 Budding
 Vegetative Propagation
 Regeneration
Advantages of
Asexual Reproduction
offspring cells are exactly like the parent
cell (clones)
Speed
Replacement
Desirable Characteristics
TRY THIS!
 On your notebook paper draw a Verbal Visual
table for Asexual Reproduction
Vocabulary Term
Definition
Drawing
Non-Example
Sexual Reproduction
Sexual reproduction requires two
parents.
Two sex cells (called gametes) must
unite.
Fertilized Egg Cell
Fertilization
Fertilization is the union of egg & sperm.
Dad
Mom
23
23
46
New
Individual
Advantages of Sexual
Reproduction
Offspring are unlike
the parent.
Sexual reproduction provides
diversity in a species.
Chromosome Number
Every species has a specific number
of chromosomes that every body cell
is supposed to have.
ant
2 chromosomes
dog
78 chromosomes
crayfish
200 chromosomes
human
46 chromosomes
Chromosome Number
Since you inherit half of your
chromosomes from each parent, you
carry two complete sets of chromosomes.
mother crayfish
100 chromosomes
crayfish
200 chromosomes
1 set of 100
1 set of 100
2 sets = 200
father crayfish
100 chromosomes
Homologous Chromosomes
These two complete sets of chromosomes
are homologous, the chromosomes from
the female parent have a corresponding
chromosome from the male parent.
mother crayfish
100 chromosomes
father crayfish
100 chromosomes
1 set of 100
1 set of 100
2 sets = 200
crayfish
200 chromosomes
Homologous Chromosomes
from
from
from
from
from
 Homologous chromosomes are
similar in size and shape and control
from the same traits.
Chromosome Number
Humans inherit one set of 23
chromosomes in the egg from the
mother and one set of 23 on the
sperm from the father.
23
This gives the child 2
23
homologous sets of
chromosomes.
46
46
46
Chromosome Number
The single set of one chromosome of
each type inherited from one parent is
called haploid.
23 Chromosomes
 Haploid:
1 set of chromosomes (n)
found in gametes (egg or sperm)
Chromosome Number
A cell (such as a fertilized egg) with two
sets of homologous chromosomes is
called diploid.
46 chromosomes
 Diploid:
2 sets of chromosomes (2n)
found in body cells (somatic)
Chromosome Number
 Why is it important for every body cell in an
organism to have the specific 2n chromosome
number for that species? .
Recall that every body cell in an organism
must have the specific 2n chromosome
number for that species.
humans must have
46 chromosomes
 If body cells do not have the correct 2n
chromosome number, the cell will not _?_.
How does this happen?
 When we grow by our cells dividing to make
two new cells, all of those new cells must have
46 chromosomes.
46
46
46
 How do we get 92 chromosomes (46 for each
new cell) from a cell with only 46
chromosomes?
Chromosome Number
The doubling of the chromosomes is
actually DNA making an exact copy of
itself. This is called DNA replication.
46
92
46
46
Then each new cell can receive the correct number
of chromosomes (DNA).
TRY THIS!
Create a Venn diagram for asexual
and sexual reproduction.
A Cell’s Life Cycle
 When does a cell divide?
 Most of a cell’s
M
life cycle is
G2
spent in
G1
Interphase when
it performs
normal life
functions.
 Green section
S
A Cell’s Life Cycle
 When does a cell divide?
M
G2
G1
Only a small
part of the cell
cycle is spent
in division.
The RED
section marked
letter M
S
A Cell’s Life Cycle
 When does DNA replication occur?
 During
M
G2
S
G1
Interphase, (in the
S/Synthesis
phase), the DNA
replicates (makes
a copy of itself).
DNA Replication
Before a cell divides the
DNA must replicate
(make an exact copy of
itself) so the new cells
have the right 2n # of
chromosomes.
DNA Replication
Each new cell must have
the same chromosome
number (and same
DNA) as the parent cell
to function properly.
DNA Replication
Replication occurs
in 3 easy steps…
DNA Replication
1. DNA Unzips
An enzyme unzips the molecule
by breaking the hydrogen bonds
that hold the nitrogen bases
together.
DNA Replication: 1. DNA Unzips
A
G
G
3’End
Left 5’ Strand of Original DNA
G
C
A
T
C
C
3’End
A
T
T
5’End
5” End
5’End
Right 3’ Strand of Original DNA
2. Bases Pair
Complementary bases match with
each base in the original DNA strand
What is the complementary base
pairing rule?
A = T
G  C
T
A
T
G
C
C
G
G
C
A
T
3’En
A
nd
DNA Base Pairing – Step 2
5’En
3. Two Identical DNA molecules
 Two new DNA molecules each have the
same DNA nitrogen base sequence.
 The new DNA molecules are
exactly like the original.
A
G
G
A
G
A
G
G
G
DNA Replication Review
Explain what is happening at each step
in DNA Replication.
Step 1
Step 2
Step 3
DNA Replication Review
 What process is
occurring?
I
 What molecule is at
I?
 What are the
structures at III
(circle)?
V
 What is happening
at II (the arrow)?
II
IV
III
V
DNA Replication Review
 What are the
new strands
like compared
to each
other?
 What is
happening
at IV??
 What are the two I
molecules at V?
II
 How many
strands are
formed?
IV
V
III
 What are the
new strands
like
V compared to
the original?
MITOSIS
Now that DNA has replicated and the cell
now has two identical sets of DNA/
chromosomes
A
A
G
G
G
G
cell division (mitosis/meiosis) can begin..
46
92
MITOSIS
What is the purpose of DNA replication?
A
A
G
G
G
G
(Hint: think of the importance to the cells
produced)
46
92
46
46
TRY THIS!
 On your paper create a 3 Column Self-
Assessment Chart for Cell Reproduction
and DNA Replication
What I
Know…
What I Don’t
Know…
What I Wish I
Knew…
Works Cited
 There is a nice animation of DNA Replication at
http://www.ncc.gmu.edu/dna/repanim.htm
 DNA Replication diagram, artist Darryl Leja, National Human Genome Research
Institute (NHGRI) http://www.genome.gov/page.cfm?pageID=10000552
 Background DNA Replicaiton image, DOE Human Genome project, Department of
Energy, (http://www.ornl.gov/hgmis)
 DNA Replication diagram, artist Darryl Leja, National Human Genome Research
Institute (NHGRI) http://www.genome.gov/page.cfm?pageID=10000552
 “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.