Announcements
•  With your group:
•  Think about a problem you would like to address
•  The problem must have a biological basis
(genetics, evolution, ecology)
•  The problem has “local” relevance.
–  MSU campus, city of Lansing/East Lansing, state of
MI, populations of college students, populations of
student athletes, mid-Michigan farmers, etc. . .
•  Think of the best examples of Public Service
Announcements you’ve ever seen
•  Bring your ideas on Tuesday!
Objectives, 9/25/08: Meiosis
1.  Model and explain how genetic information is
transferred from one generation of cells to
the next via the processes of mitosis and
meiosis
2.  Transfer and apply the model and
explanation in multiple contexts and cases
3.  Compare and contrast cell division by mitosis
with cell division by meiosis
4.  Represent chromosomes containing specific
alleles through cell division by mitosis and
meiosis
From last time:
•  Mitosis – one form of cell reproduction
•  Results in production of 2 daughter cells
–  Genetically identical to each other
–  Genetically identical to parent cell
•  Purpose: growth, tissue repair, asexual
reproduction
•  Occurs in somatic (body) cells
N
Ploidy
a. 2
a. 1
b. 3
b. 2
c. 4
c. 3
d. 6
d. 4
e. 12
e. 12
YouTube Video: Mitosis
•  http://youtube.com/watch?v=VlN7K1-9QB0
YouTube Video: Meiosis
•  http://youtube.com/watch?v=47vf2m-Iyb8
Meiosis: sex
Products?
Where does this
occur?
Draw a cell containing 2
pairs of homologous
chromosomes for the
individual to the right.
She is heterozygous for
tongue rolling and earlobe
shape.
The cell is in G2 (DNA is
replicated).
T
t
T
t
f
F
F
f
Cell Division by Meiosis
Two Divisions:
1. Meiosis 1: Homologs Separate
2. Meiosis 2: Sister Chromatids Separate
Draw your cell with the
homologs aligned at the
equatorial plane.
T
T
F
F
t
t
f
f
Metaphase 1:
How is this
different from
metaphase of
mitosis?
Homologs align at equatorial
plane
T
T
F
F
t
t
f
f
The cell divides. Homologs
are sorted into different
daughter cells.
Draw the products of this
division.
Metaphase –
Anaphase 1:
Homologs separate
T
T
F
F
t
t
f
f
End of Meiosis 1: Homologs separate into 2 cells
T
F
T
F
t
t
f
f
End of Meiosis 1: Homologs separate into 2 cells
T
T
Ploidy = ?
t
t
A. 1
B. 2
C. 4
D. 8
F
F
f
f
What is consequence of separating the homologs?
T
F
T
F
t
t
f
f
Mendel’s Laws
1. Principle of Segregation
–  Diploid organisms have pairs of alleles
–  Individual alleles in the pair separate during meiosis
Why? In meiosis 1, homologous chromosomes separate.
Therefore, the alleles on the homologous chromosomes
also separate.
Each cell resulting from meiosis 1
undergoes a second division.
Meiosis 2:
T
F
T
F
t
t
f
f
Chromosomes line up at
equatorial plane by centromere
Metaphase 2:
T
F
T
F
t
t
f
f
Each daugher cell from
meiosis 1 divides. Sister
chromatids are sorted into
different daughter cells.
Draw the products of this
division.
Metaphase –
Anaphase 2:
T
F
Sister chromatids separate into
daughter cells
T
F
t
t
f
f
End of Meiosis 2: Daughter cells are
“gametes” (eggs and sperm).
T
F
T
F
t
f
t
f
What if homologs lined up differently at
Meiosis 1?
T
T
F
F
t
t
f
f
Predict the genotypes of gametes
T
T
t
f
f
F
t
F
Predict the genotypes of gametes
T
T
t
f
f
F
t
F
Predict the genotypes of gametes
T
T
f
f
t
F
t
F
Genotypes of gametes?
T
T
f
f
t
t
F
F
Why are the genotypes different?
T
T
f
f
t
t
F
F
Mendel’s Laws
1. Principle of Segregation
–  Diploid organisms have pairs of alleles
–  Individual alleles in the pair separate during meiosis
Why? In meiosis 1, homologous chromosomes separate.
Therefore, the alleles on the homologous chromosomes
also separate.
2. Principle of Independent Assortment
–  Different pairs of alleles on different chromosomes
separate independently of each other during meiosis.
Why? In meiosis 1, the arrangement of homologous
chromosomes on either side of the equatorial plane is
random.
What is the consequence of Independent
Assortment?
T
T
F
F
t
t
f
f
Can we predict the
number of
different types of
gametes that
could be formed?
i.e., How many
different allele
combinations
(genotypes) could
you get in the
gametes?
t
t
T
F
F
f
f
T
How many different kinds of gametes could be
formed by YOU? (or any human being)
TF
T
T
Tf
t
t
tF
tf
F
= 2n
F
f
f
(for diploid
organism, where n
is the number of
homologous pairs)
Use a sheet of plain white paper with your:
Name, Group Name and PID.
Think about a model that has the function of
explaining cell division via mitosis and
meiosis. Brainstorm with your group to:
1.  Decide if the model would be linear,
branched, or cyclical. Explain why.
2.  List the “structures” you would expect to use
in this model.
3.  List the “behaviors” you expect to use in this
model.
Turn in one per individual.