Penny Genetics Lesson Plan Teacher Lesson Plan
Penny Genetics Lab
Duration: 60 Minutes | Topic: Genetics & Probability
MA State Standards (STE)
HS-LS3-3: Explain the causes and consequences of genetic variation, including Mendelian inheritance and the effects of fertilization on variation.MS-LS3-2: Develop and use a model to describe how sexual reproduction results in offspring with genetic variation.
Learning Objectives
Students will model Mendelian inheritance (fertilization) using a coin-flip simulation.
Students will compare theoretical probability (Punnett Squares) with experimental data (actual ratios).
Students will analyze how sample size affects the accuracy of genetic predictions.
Language Objectives
Define and use academic vocabulary: genotype, phenotype, allele, ratio, and probability.
Construct comparison statements using comparative adjectives (e.g., "The actual ratio was closer to the predicted ratio...").
Required Materials
Penny Genetics Lab Sheets
2 Pennies per pair
Masking tape or markers
Class data tracking sheet
Class Schedule (60 Min)
0-10 min
Hook & Review
Review homozygous vs heterozygous. Show a Punnett Square and ask: "Is this a guarantee of what the baby will look like?"
10-15 min
Lab Setup & Demo
Demonstrate labeling coins. Explain that one flip = one gamete donation. Two flips together = fertilization.
15-45 min
Lab Phase (Active)
Students flip 100 times for Tt x Tt, then switch to Tt x tt. Monitor tally marks for consistency.
45-55 min
Data Aggregation
Aggregate "Short Toe" vs "Long Toe" counts from every group on the board. Compare individual group data to the massive class total.
55-60 min
Analysis & Debrief
Students complete the Analysis section. Focus on Question 4 regarding sample size accuracy.
Essential Discussion Questions
Q1: "If a group flipped 10 times and got 10 long toes, does that mean their Punnett Square was wrong? Why?"
Q2: "In real life, why don't families with four children always have exactly one child with the recessive trait?"
Q3: "How did our class total compare to the 75%/25% prediction? What does this tell us about sample size?"
Teacher Note: Common Misconceptions
Students often think that if a Tt x Tt cross results in a recessive offspring, the "next" offspring is "due" to be dominant. Remind them that each flip (fertilization) is an independent event, just like a coin flip has no memory of the previous result.
Penny Genetics Slides Penny Genetics
Predicting Ratios vs. Real Life Reality
The Science of Chance
The Big Question
How well does a Punnett Square predict what happens in actual life?
Theory
vs
Reality
The Trait: Short Big Toe
T
Dominant
Short Big Toe
t
Recessive
Long Big Toe
Genotypes: TT (Short), Tt (Short), tt (Long)
The Theoretical Prediction
<table class="w-[450px] h-[450px] border-4 border-teal-600 text-center text-5xl font-bold bg-white"><tbody><tr class="bg-teal-600 text-white"><td class="border-4 border-teal-600"></td><td class="border-4 border-teal-600 py-6">T</td><td class="border-4 border-teal-600 py-6 italic">t</td></tr><tr><td class="border-4 border-teal-600 bg-teal-600 text-white px-8">T</td><td class="border-4 border-teal-600 py-12">TT</td><td class="border-4 border-teal-600 py-12">Tt</td></tr><tr><td class="border-4 border-teal-600 bg-teal-600 text-white px-8 italic">t</td><td class="border-4 border-teal-600 py-12">Tt</td><td class="border-4 border-teal-600 py-12">tt</td></tr></tbody></table>
Probability:
75% Short Toe25% Long Toe
Lab Instructions
1
Label two pennies. One side T , one side t .
2
Flip both coins at once. This represents Fertilization .
3
Tally the outcome (TT, Tt, or tt). Repeat 100 times .
Class Data Challenge
Individual groups might be "off."
Will it match the Punnett square?
Penny Genetics Lab Sheet Penny Genetics Lab
Predicting Ratios vs. Experimental Reality
Names:
Date:
In this lab, you will use Punnett Squares to make predictions, then use pennies to simulate crosses . Finally, you will compare the Actual Ratios from your flips with the Predicted Ratios .
The Trait: Short Big Toe
T = Dominant (Short big toe) | t = Recessive (Long big toe)
Genotype Phenotype (Description) T T T t t t
Chart A: Predicted Ratios
Predict offspring for parents: Tt x Tt
T
t
T
t
Expected % (out of 100):
TT Short Toe:
Tt Short Toe:
tt Long Toe:
*These are your PREDICTED ratios.
Actual Ratio Simulation
Use two pennies. Both represent a parent with genotype Tt .
Partner A flips for the "Male" parent.
Partner B flips for the "Female" parent.
Combining the flips = Fertilization .
Practice Flips
Did you get a TT, Tt, or tt? Phenotype?
Chart B: Actual Ratios (100 Flips)
Combination Tally Marks Total TT Tt tt Total Flips: 100
Final Phenotype Count
Short Toe (TT + Tt):
Long Toe (tt):
Flip exactly 100 times before moving to the comparison section.
Comparing Actual to Predicted Ratios
Predicted Ratios (Chart A) Actual Ratios (Chart B) TT Tt tt
Penny Genetics Answer Key Answer Key & Teacher Reference
Penny Genetics Lab
Part 1: Tt x Tt Cross (Heterozygous)
Genotype to Phenotype:
TT: Short Toe (Dominant Homozygous)Tt: Short Toe (Heterozygous)tt: Long Toe (Recessive Homozygous)
Predicted Counts (per 100 flips):
TT (25%) 25 out of 100Tt (50%) 50 out of 100tt (25%) 25 out of 10075% Short Toe / 25% Long Toe
Part 2: Tt x tt Cross
<table class="w-32 h-32 border-2 border-slate-400 text-center bg-white"><tbody><tr><td class="border border-slate-300"></td><td class="border border-slate-300 font-bold italic">t</td><td class="border border-slate-300 font-bold italic">t</td></tr><tr><td class="border border-slate-300 font-bold">T</td><td class="border border-slate-400 font-bold bg-teal-50">Tt</td><td class="border border-slate-400 font-bold bg-teal-50">Tt</td></tr><tr><td class="border border-slate-300 font-bold italic">t</td><td class="border border-slate-400 font-bold italic bg-teal-50">tt</td><td class="border border-slate-400 font-bold italic bg-teal-50">tt</td></tr></tbody></table>
Expected Results:
50% Short Toe (Tt)
50% Long Toe (tt)
Analysis Solutions
1. TT x Tt cross prediction:
Offspring will be 50% TT and 50% Tt. Phenotypically, this is 100% Short Toe.
2. What do the individual pennies represent?
The parents (specifically their genotype). One penny represents the maternal alleles and the other represents paternal alleles.
3. What biological process is being simulated?
Meiosis (segregation of alleles into gametes) and random fertilization.
4. Why does the class total match better?
The Law of Large Numbers. Larger sample sizes reduce the impact of random variance, making experimental data align closer to theoretical probability.
