Name __________________________________________________________________________ Period ____
Coin Toss Genetics
The way genes behave during meiosis and fertilization can be modeled by using two-sided coins, where heads
represent the dominant allele (A) and tails represent the recessive allele (a). This table explains how the coin toss
model of inheritance represents the biological processes of meiosis and fertilization for heterozygous (Aa) parents.
Biological Process
How This Will Be Modeled in Coin Toss Genetics
Meiosis in an Aa parent produces gametes. Each
You toss your coin and check for heads up vs.
gamete has an equal probability of having an A allele tails up. This represents the equal probability of
or an a allele.
getting an A allele or an a allele.
Fertilization of an egg by a sperm produces a zygote. Two students each toss a coin and the result of
Each gamete contributes one allele to the genotype
this pair of coin tosses indicates the genotype of
of the child that develops from the zygote.
the child that develops from the zygote.
 Find someone to “mate” with.
 Each of you will toss your coin. Record the results as the genotype of the first child in the first family of four
children in the table below. Make three more pairs of coin tosses and record the genotypes for the second,
third and fourth children in this family.
Genotypes of coin toss children produced by two heterozygous (Aa) parents
Genotype for each child
Number with each genotype
1st
2nd
3rd
4th
AA
Aa
aa
First family of 4 children
Next family of 4 children
Next family of 4 children
Next family of 4 children
Totals
 Repeat this procedure three times to determine the genotypes for three more families of four children each,
and record your results in the table.
 Complete the last three columns for these four families of coin toss children. Calculate the totals for the AA, Aa
and aa genotypes, and give your teacher these totals.
1a. Draw a Punnett square for two Aa parents in this rectangle.
1b. For a family of 4 children, the predicted number of children with each
genotype is ____ AA, ____ Aa, and ____ aa.
1c. How many of your coin toss families had exactly these predicted numbers of
AA, Aa and aa genotypes?
To understand why some of the coin toss families do not have exactly the predicted number of children with each
genotype, answer the following questions.
2. Does the genotype produced by the first pair of coin tosses have any effect on the genotype produced by the
second pair of coin tosses? ___ yes ___ no
3. If a coin toss family has one aa child, what is the probability that the second child in this family would also have
the aa genotype? ___0%
___25% ___50% ___75% Explain your reasoning.
Name __________________________________________________________________________ Period ____
In real families the genotype of each child depends on which specific sperm fertilized which specific egg. This is not
influenced by what happened during the fertilizations that resulted in previous children. Therefore, the genotype
of each child is independent of the genotype of any previous children.
4. Think about real families where both parents are heterozygous Aa and each family has four children. Would each
of these families have exactly one albino child, as predicted by the Punnett square? Explain why or why not.
5a. Complete this table. Your
teacher will provide the data
for the bottom row.
% AA % Aa % aa
Prediction based on Punnett square
Class data for coin toss children
5b. Explain why the class data are closer to the Punnett square predictions than some of the individual families in
your coin toss data.