Name _______________________________________________
Date _______________
Activity: Coin Toss
Goal:
1. To observe how traits are distributed to offspring.
2. To calculate the percentages of the dominant and recessive traits during a coin
toss activity.
Background Information: Genetics is the study of heredity, or passing on of traits from
one organism to its offspring. For each trait, every organism has a pair of factors, or
units of heredity, called genes. These units of heredity come from the parents of the
offspring. One of each pair comes from each parent. The dominant of the two genes
masks the recessive gene. If the pair is made of two of the same forms of the gene (for
example two dominant alleles or two recessive alleles), the offspring are homozygous
for that trait. If the pair is made of two different forms of the gene (for example one
dominant allele and one recessive allele), the offspring are heterozygous for that trait.
Gregor Mendel studied traits of pea plants. He studied two varieties of pea plants: tall
and short-stemmed plants. Mendel discovered that when he planted the seeds from
short-stemmed plants, the offspring were only short-stemmed plants, but when he
planted tall plants, short plant were sometimes produced. Mendel concluded that there
must be two factors that controlled the trait for shortness and tallness. When both
factors (genes) were present in a plant, only the tallness trait was expressed. He
reasoned that the factors (genes) that controlled tallness were dominant and masked
the shortness factor. Mendel observed, however, that under certain conditions, short
plants could be produced from tall plants.
Materials: Two coins (each coin should be marked with a capital T (T) on one side and
a lowercase T (t)) on the other side.
Procedure:
KEY:
T – Dominant Trait
t – Recessive Trait
1. What I Know: Write a sentence or two about what you already know about
genetics and probability.
2. Obtain two marked coins. Each coin is marked with an uppercase (T) on one
side, and a lowercase (t) on the other side.
3. Toss both coins, together for a total of 100 times. Each coin represents the
alleles for a parent; therefore the cross represented by the coin tosses is Tt XTt.
Both parents are heterozygous for height.
4. Record the genotype for each coin toss (TT, Tt, tt).
5. The possible genotypes are as follows:
 TT – purebred dominant or homozygous dominant
 tt – purebred recessive or homozygous recessive
 Tt – hybrid or heterozygous
6. Record the data on your chart on your lab sheet. Complete the tally chart and
determine the total number of genetic combinations and percentages that
resulted from your tosses.
7. What I Observed: This will be the data table you completed.
Tally of Dominant and Recessive Traits
# of TT = ______
% of TT = ______
# of tt = ______
% of tt = ______
# of Tt = ______
% of Tt = ______
# of TT + Tt = _______
(All of the tall plants)
___
% of TT + Tt = _______
(All of the tall plants)
8. What I Did: Write a summary of the procedure you used during this activity.
9. What I Learned: Describe what you learned from this activity.
10. What I Wonder: Pose one question that you still have about the topic of
genetics and probability.
11. Questions: Answer the following questions in complete statements.
a. What did the capital T and the lowercase t represent on the coins?
b. What were the genotypes of the parents?
c. What were the phenotypes of the parents?
d. What were the percentages for each genotype?