Mendel’s Mighty Missing Meiotic Mechanism
University of North Carolina, Chapel Hill
Jean DeSaix
Kelly Hogan
University of California, Santa Barbra
Rolf Christoffersen
Stu Feinstein
Kansas State University
Eva Horne
Robbie Bear
With special thanks to
Kathrin Stanger-Hall
and
Jess Blum
Teachable Unit: Heredity
Topic: Connecting Meiosis with Mendelian Inheritance
Context: Large Introductory Biology Course.
Assumed Basic Knowledge:
• Chromosome segregation into gametes during
meiosis
• Mendelian inheritance
Learning Goal :
How meiosis relates to the inheritance of alleles
of two traits.
Learning Outcome for Teachable Tidbit:
Predict how the arrangement of chromosomes in
meiosis I will determine the allele combinations in
a Punnett Square.
Tidbits
A = active
a = passive
B = big
b = little
AaBb
aabb
Active & Big
passive & little
Tidbit
Gonad
Single cell
B
B
Each person = chromosome
Color indicates parental origin
- pink = maternal origin
- blue = paternal origin
Letter = allele
Check your vocabulary…
What is the relationship between the chromosome carrying the “A”
allele and the chromosome carrying the “a”allele?
Homologs - same genes, can be different alleles
Is a Tidbit gonad cell a diploid or a haploid cell and how do you
know?
Diploid
vs.
Haploid
Two sets of all chromsomes.
Example: AABB
One set of all chromosomes.
Example: AB
You are all the
directors of this
show!
What needs to happen before we start
our production of meiosis?
Check your vocabulary…
Homologs - same genes, can be different alleles
What is the relationship between the chromatid carrying the “a” allele
and the other chromatid attached to it carrying the “a”allele?
Sister chromatids - same genes, identical alleles
At metaphase I, how should the alleles be
arranged on the metaphase plate?
A)
B)
A A
A A a a
B B
a a
b b
C)
B B b b
D)
A A
A A a a
b b
a a
B B
b b B B
At metaphase II, how should the alleles be
arranged on the metaphase plate?
A)
B)
A A
a a
B B
b b
A A
a a
b b
B B
B BA A
b ba a
C)
D)
a a
A A
b b
B B
When the actors did this, why did
we only get half of the expected
types of gametes?
A A a a
A A a a
Gonad
b b B B
b b B B
A A a a
A A a a
B B b b
B B b b
How can we get all of the
possible gamete types?
B)
Homework:
Draw the two cells that would
result from meiosis I for
options B and D.
A A a a
B B b b
D)
A A a a
Then draw the outcome of
meiosis II for both options
b b B B