Breaking
(Down) the
Law:
Mendel’s Laws
May 17, 2013
Athens, GA
Heredity Group AKA
“The Chiasmatics”
Unit Context
 Introductory
 2-3
level majors biology
Weeks, OR As long as it takes to
achieve the learning objectives
Unit Learning Goal
 Students
will understand how allelic
segregation and independent
assortment result in inheritance of
characteristics through the process of
meiosis and sexual reproduction.
Unit Outcomes
 Define
terms(Knowledge) and describe their
hierarchical relationships (Comprehension):
locus, gene, alleles, DNA, chromosomes,
gametes, segregation, independent
assortment
 Explain the process of segregation and
independent assortment and how it relates to
crosses. (Comprehension)
 Given parental genotype of a cross, predict
phenotypic and genotypic frequency for two
traits using Punnett square. (Application)
Unit Outcomes
• Given a phenotypic ratio, infer parental
genotypes (Analysis)
• Create a diagram that demonstrates the
segregation of alleles at two independentlyassorting genes during gamete formation.
(Synthesis)
• Diagram how the process of meiosis gives rise to
gametes for two independently-assorting traits.
(Synthesis)
• Given a set of data, determine if the data
provided fit a particular type of inheritance.
Provide a possible explanation to support your
inference (Evaluation).
Tidbit Rationale:
Why did we choose this particular
learning objective?
 Relative
importance of this topic as a
foundation for future concepts
(scaffolding)
 Difficult
concept for students to learn
(high abstraction and cognitive load)
 Many
misconceptions about this topic
and its connection to meiosis
Prior Knowledge:
Students
will…
Understand DNA as genetic
material (allele, chromosome)
Understand meiosis and
sexual reproduction
Understand and complete
monohybrid crosses.
X
AA
aa
?
What is the genotype of the offspring?
A)
B)
C)
D)
Aa
aa
AA
BB
Tidbit Step 1


Open envelope #1, which contains 8
pieces of paper each of which
represents an allele (A, a, B, b).
Use these pieces of paper to create all
the possible gametes produced by a
heterozygous parent through
independent assortment.
Review Question
 Looking
at your cards, what does
each letter represent?
A.
B.
C.
D.
Chromosome
Allele
Gene
Gamete
Review Question
 Looking
at your cards, what do the
upper versus lower case letters
represent?
A.
B.
C.
D.
E.
Dominant vs. Recessive Alleles
Dominant vs. Recessive Genes
Genotype vs. Phenotype
Homozygous vs. Heterozygous
Male vs. Female Gamete
Review Question
 What
cell division process creates the
haploid cells that become or
produce gametes?
A)
B)
C)
D)
Mitosis
Meiosis
Fission
Budding
Clicker Question
 Which
of the following is the correct set
of possible gametes for your cards?
A.
B.
C.
D.
E.
AA, Aa, BB, Bb
A, B, a, b
AB, ab, AB, ab
aa, bb, BB, AA
AB, Ab, aB, ab
Tidbit Step 2
 We
need 8 student volunteers.
 Please
 You
grab one sign from the table.
are a chromosome from a
diploid organism with two
chromosome pairs (see diagram
above).
Tidbit Step 3
 Organize
 Prompt



yourselves into gametes.
questions
Are gametes haploid or diploid?
Do gametes have two copies of the same
gene?
Is this all the possible combinations?
Tidbit Step 4
 Line
up students horizontally at front
of class
Tidbit Step 5


Now open the second envelope ,
which contains 8 more pieces of
paper each of which represents an
allele (A, a, B, b).
Use these pieces of paper to create
all the possible gametes from the
heterozygous male parent.
Tidbit Step 6
 We
now need 8 more volunteers.
 Please
grab a card and organize
yourselves into gametes.
 Line
up at a right angle to original
group (e.g. on left aisle of the
classroom).
Clicker Question
 Notice
that each of the two groups
have slightly different color shades
(bright and pale). What do the two
shades represent?
A)
B)
C)
D)
Different alleles
Different genes
Different chromosomes
Different sexes
Tidbit Step 7
 What
have we just created?
 Now sit down and check your cards
and rearrange them so that they
match what we have created.
A
AA
Aa
aA
aa
B
AB
BB
AB
Bb
Ab
bB
aB
bb
ab
Ab
aB
ab
Which Punnett square represents a cross between two heterozygous parents?
C
AA
AA
BB
BB
D
AA
aa
BB
aa
BB
bb
bb
bb
bb
AA
aa
aa
Clicker Question
 What
does each two-letter combination
(e.g., AB) represent, assuming
independent assortment?
A)
B)
C)
D)
Alleles from 2 genes on 1 chromosome
Alleles from 2 genes on 2 different
chromosomes
2 alleles from 1 gene
The same allele from different sexes
On paper, identify the different parts of the Punnett square
numbered below.
1
3
AB
Ab
aB
Ab
AB
Ab
aB
Ab
2
Summative Assessment
Questions:
1.
Reflection: Summarize the activity that
we completed in class today using the
following terms: alleles, independent
assortment, meiosis, gamete, and
random segregation.
2.
Assume a simple dominant inheritance
pattern in peas with Y = green, y =
yellow, R = round, and r = wrinkled.
Find the genotypic and phenotypic
ratio from the following two crosses
a.
b.
RrYy x RrYy
RrYy x rryy
Possible Extensions
1.
Use this human demonstration technique to
model meiosis and gamete formation.
2.
Extend the human Punnett square here to show
a male and female gamete joining to produce
an offspring. (Or even using lots of volunteers to
show all possible offspring combinations in the
Punnett square – this would require 64 additional
volunteers and appropriate space to create the
entire Punnett square.)
3.
Let the letters represent alleles for real world
traits to make the process more tangible.
References I
 Mbajiorgu.
(2007). Science Education,
91(3), 419-438.
 Kibuka-Sebitosi. (2007). J. o. Biological
Education, 41(2), 56-61.
 Brown. (1990). J. o. Biological Education,
24(3), 182-186.
 Smith. (1991). J. o. College Science
Teaching, 21(1), 28-33.
 Oztap, Ozay, & Oztap (2003). J. o.
Biological Education, 38(1), 13-15.
References II
 Dikmenli.
(2011). Scientific Research &
Essay, 5(2), 235-247.
 Ozcan, Yildirim, & Ozgur. (2012).
Procedia – Social & Behavioral
Research, 46, 3677-3680
 Karagoz & Cakir. (2011). Educational
Sciences: Theory & Practice, 11(3), 16681674.
 Sesli & Kara. (2012). J. o. Biological
Education, 46(4), 214-225.