Probability, Inheritance and Punnett Squares – Lesson
Plan
Linked to CK-12 Concepts:
1. Probability, Inheritance
2. Punnett Squares
Class: (Customize to your use)
Date: (Customize to your use)
Standard(s): (Customize to your use)
Learning Activities and Timing: (Customize to your use. View this
concept’s “Additional Resources” for access to even more useful
materials.)
Key Objective(s):
Concept Objective(s):
Explain how probability is related to inheritance.
Describe how to use a Punnett square
Explain how Mendel interpreted the results of his experiments.
Language Objective(s):
Follow precisely a complex multistep procedure when carrying out experiments, taking
measurements, o performing technical tasks, attending to special cases or exceptions defined in
the text.
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Exit Criteria:
When students finish this lesson, they should be able to use probability to determine progeny
outcome in a single allele with Punnett squares.
1. Define probability. Apply the term to a coin toss.
2. What is a Punnett square? How is it used?
3. Recall today’s content and language objective. Evaluate whether you have met these
objectives. Based on your own evaluation, put your paper in one of these categories;
“Clueless, More practice, Sort of got it, I totally understand.”
**To help the teacher gauge their student learning, you can have students evaluate themselves
on the content and language objective with their completed exit tickets. Have students place in
their papers into one of these four categories; “Clueless, More practice, Sort of got it, I totally
understand.”**
Teaching Strategies and Tips:
Based on probability and knowledge of Mendelian inheritance, a Punnett square can be used to
predict the proportions of different genotypes in the offspring of a given set of parents. Mendel
didn’t know about genes, but luckily he studied simple dominant-recessive traits, so he could
work backward from phenotypes to determine the pattern of inheritance. More complex
patterns of inheritance include codominance, incomplete dominance, multiple alleles, multiple
genes, and environmental influences on gene expression.
Introducing the Lesson:
Have students chorally read out loud the Concept and Language objective two times and
have them write it down in their notes.
Demonstration
Toss a coin to see if a head or tail turns up, after first asking the class to predict the outcome of
the toss. Use the coin toss as a vehicle to introduce the concept of probability. Tell students
they will learn how probability is related to heredity when they read this lesson.
Interactive Web Activity
Assign the drag-and-drop activity at the URL below. Students will use Punnett squares to
determine expected proportions of genotypes and phenotypes of offspring.
http://www.zerobio.com/drag_gr11/mono.htm
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* E. Kimmel, (2005). Drag and Drop Genetics. Retrieved on July 3rd, 2012 from
http://www.zerobio.com/drag_gr11/mono.htm
Science Inquiry:
Laboratory
This laboratory is mainly practice of students being dragon gametes. They must use Punnett
Squares and their probable outcome to determine their offspring. There are 13 traits in which
students have to work with. Please see “ProbabilityInheritancePunnettSqLab” under Resources
tab.
* Dragon Genetics Updated is used from owner’s (Andrea Trosien) permission.
* Trosien, Andrea. (2012). Dragon Genetics Updated. File received via email June 26th, 2012.
Permission given by owner.
Adapted from Dragon Genetics, Pleasant Valley Junior High School, Pleasant Valley High
Community School District, (No Date). Dragon Genetics Lab: Principles of Mendelian Genetics
[PDF document]. Retrieved on June 28th, 2012 from
http://www.pleasval.k12.ia.us/juniorhigh/Teachers/runklet/LS1%20Handouts/4%20Unit%204/D
ragon%20Lab.pdf
Differentiated Instruction:
Coin Toss Genetics
Students will use Punnett squares to predict the probable outcomes of species. Coins will help
determine their alleles. Student handout “ProbabilityInheritancePunnettSqDiffInstr” can be
found under “Resources” tab. Teacher key and instructions can be found in Teacher’s Version.
* Serendip, Bryn Mawr College. (August, 2011). Genetics. Retrieved on July 3rrd, 2012 from
http://serendip.brynmawr.edu/sci_edu/waldron/#dragon1
Common Misconceptions:
Students commonly think that the expected proportions of genotypes in offspring, as given in a
Punnett square, are the actual proportions. Explain that they are only the most likely
proportions, and other proportions may occur in any given family.
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Enrichment:
Web Activity
Punnett Squares
Have students who need extra challenges solve the case study Those Old Kentucky Blues at the
URL below.
In this honors activity, they will use pedigrees and other information to determine the
inheritance pattern of an interesting genetic condition.
http://sciencecases.lib.buffalo.edu/cs/collection/detail.asp?case_id=208&id=208
* Leander, Celeste A., Department of Biology and Zoology, The University of British Columbia.
(2010) Those Old Kentucky Blues. Retrieved on July 3rd, 2012 from
http://sciencecases.lib.buffalo.edu/cs/collection/detail.asp?case_id=208&id=208
Review Questions:
1. How is gamete formation like tossing a coin?
2. Draw a Punnett square of an Ss x ss cross. The S allele codes for long stems in pea plants
and the s allele codes for short stems. If S is dominant to s, what percentage of the offspring
would you expect to have each phenotype?
3. What letter should replace the question marks (?) in this Punnett square? Explain how you
know.
4. How do the Punnett squares for a monohybrid cross and a dihybrid cross differ?
5. Mendel carried out a dihybrid cross to examine the inheritance of the characteristics for seed
color and seed shape. The dominant allele for yellow seed color is Y, and the recessive allele for
green color is y. The dominant allele for round seeds is R, and the recessive allele for a wrinkled
shape is r. The two plants that were crossed were F1 dihybrids RrYy. Identify the ratios of traits
that Mendel observed in the F2 generation, and explain in terms of genotype what each number
means. Create a Punnett square to help you answer the question.
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6. Mendel investigated stem length, or height, in pea plants. What if he had investigated human
height instead? Why would his results have been harder to interpret?
7. Assume you are investigating the inheritance of stem length in pea plants. You crosspollinate a short-stemmed plant with a long-stemmed plant. All of the offspring have long
stems. Then, you let the offspring self-pollinate. Describe the stem lengths you would expect to
find in the second generation of offspring.
Solution Guide:
Answers to the Exit Criteria, and Review Questions will be available here with the Teacher
version.
Other answers generated from additional student handouts such as laboratory or any other
introductory, differential and scientific inquiry activities will have a separate example or answer
key available to the teachers. Thank you!
Points to Consider:
Like most of the characteristics of living things, the characteristics Mendel studied in pea plants
are controlled by genes. All the cells of an organism contain the same genes, because all
organisms begin as a single cell. Most of the genes code for proteins.
- How is the information encoded in a gene translated into a protein? Where does this occur,
and what processes are involved?
Students may or may not be familiar with the processes of protein synthesis — transcription and
translation — and the role of ribosomes in the latter process.
- If cells have the same genes, how do you think different cells arise in an organism? For
example, how did you come to have different skin, bone, and blood cells if all of your cells
contain the same genes?
– Sample answer: I think that different genes are translated into proteins in different cells.
Homework:
Students can practice their understanding of Mendelian Genetics. This document can be found
as “ProbabilityInheritancePunnettSqHmk” under Resources tab.
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*Trimpe, T., Science Spot. (2006). Bikini Bottom Genetics Review. Retrieved on July 3rd, 2012
from http://sciencespot.net/Pages/classbio.html#Anchor-genetics
Additional Resources:
Practice I
Use this resource to answer the questions that follow.
Fundamentals of Inheritance at http://www.biologie.uni-hamburg.de/bonline/library/falk/Inherit/Inherit.htm.
1. Define probability as a sentence.
2. Define probability as a fraction.
3. What is the probability of cutting a deck of playing cards and getting an ace?
4. How can you determine the probability of two independent events that occur together?
5. What is the probability that two heterozygous individuals will have offspring with
attached earlobes?
Practice II
Use this resource to answer the questions that follow.
http://www.hippocampus.org/Biology
Biology for AP*
Search: The Punnett Square
1. What is a Punnett square?
2. What is the size of a Punnett square used in a dihybrid cross?
3. Define the following terms: alleles, genotype, phenotype, genome.
Web Animation
At the link below, you can watch an animation in which Reginald Punnett, inventor of the
Punnett square, explains the purpose of his invention and how to use it.
http://www.dnalc.org/view/16192-Animation-5-Genetic-inheritance-follows-rules-.html
* * Cold Spring Harbor Laboratory, (No Date), Genetic Inheritance Follows Rules. Retrieved on
July 3rd,2012 from http://www.dnalc.org/view/16192-Animation-5-Genetic-inheritance-followsrules-.html
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Video
An explanation of Punnett squares can be viewed at
http://www.youtube.com/user/khanacademy#p/c/7A9646BC5110CF64/13/D5ymMYcLtv0
(25:16).
* Khanacademy, (September 30th, 2009) Punnett Square Fun. Retrieved on July 3rd, 2012 from
http://www.youtube.com/user/khanacademy#p/c/7A9646BC5110CF64/13/D5ymMYcLtv0
An example of the use of a Punnett square can be viewed at
http://www.youtube.com/watch?v=nsHZbgOmVwg&feature=related (5:40).
* imwondering, (February 15th, 2009) Punnett Square to Determine Possible Blood Types.
Retrieved on July 3rd, 2012 from
http://www.youtube.com/watch?v=nsHZbgOmVwg&feature=related
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