Activity 1
In this activity you will see how the laws of chance relate to biological occurrences. Mendel realized the role
of chance in heredity and it was a radical concept for its time.
Materials (per team of two students)
Two coins (which can be different types).
Background information and Questions
Fortunately for casino operators, many people do not truly understand the statistics behind random chance.
For an event that is truly random (contrary to the rumor, coins flips really are random), the previous results
have no bearing on the next outcome. A coin that has flipped tails up three times in a row doesn’t “know”
that it is “due” so the next flip is still random.
What are the odds of a normal coin landing heads up after being flipped?
What is the probability (odds) of two coins both landing heads up after being flipped? (Hint: the probability
of a sequential event is the probability of each event separately, multiplied together.)
What is the probability of three coins all landing heads up after being flipped?
Imagine three coins are flipped, but one at a time. The first two coins both land heads. What are the odds of
the last coin landing heads up?
Procedure
1. Complete the Punnett squares below. (A = any generic dominant trait; a = any generic recessive trait)
a) Aa x Aa cross
b) Aa x aa cross
a) Record the genotype and phenotype ratios for the Aa x Aa cross.
b) Record the genotype and phenotype ratios for the Aa x aa cross.
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2. Create a Punnett square to predict the outcome of tossing two coins (assume heads is one allele and tails
is the other, neither is dominant).
3. Flip or toss your two coins 100 times (Yes, you have to do it 100 times). Put tallies in the top boxes and
then count the tallies and write the number in the total row of the table.
Heads/Heads
Heads/Tails
Tails/Tails
Actual total
Predicted
3a. Fill in the predicted number (based out of 100 flips) of each category based on your Punnett square
from question #1.
 Do the actual results match your prediction? Explain why they do or do not.
4. If you toss the coins 1000 times instead of 100, would you expect the actual and predicted numbers to
match more closely than you saw after 100 flips, be the same as after 100, or become very different?
Explain.
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