Name ___________________________________________
Period ______
Date ______________
Probability Problems
1. In humans, curly hair is dominant over straight hair. A woman heterozygous for hair curl
marries a man with straight hair and they have children.
a. What is the genotype of the mother? ___________________________________
b. What gametes can she produce? ___________________________________
c. What is the genotype of the father? ___________________________________
d. What gametes can he produce? ___________________________________
e. What is the probability that their first child will have curly hair? _________________
f. What is the probability that their second child will have curly hair? ________________
2. List all the gametes that are possible with each of the following genotypes:
a. Aabb __________________________
d. AABb __________________________
b. AaBB __________________________
e. AAbb __________________________
c. AaBb __________________________
f. aabb __________________________
3. What is the probability of getting the gamete (ab) from each of the following parents?
a. Aabb __________________________
d. AABb __________________________
b. aaBb __________________________
e. AAbb __________________________
c. AaBb __________________________
f. aabb __________________________
4. In a certain strain of mice, black coat (B) is dominant over white coat (b). Describe what you
would do to determine the genotype of a male with a black coat and how this would enable
you to choose between the genotypes BB or Bb.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
5. What is the probability of each of the following sets of parents producing the given genotypes
in their offspring?
Parents’ Genotype
Aa x Aa
Aa x aa
AaBb x AaBB
AaBb x AABb
AaBb x AaBb
Offspring Genotype
Aa
Aa
AABB
aabb
AaBb
Probability
6. If an offspring has the genotype Aa, what possible combinations of parental genotypes could
have produced this offspring?
7. In corn, the trait for tall plants (T) is dominant to the trait for dwarf plants (t) and the trait for
colored kernels (C) is dominant to the trait for white kernels (c). In a particular cross of corn
plants, the probability of an offspring being tall is 1/2 and the probability of a kernel being
colored is 3/4. Which of the following most probably represents the parental genotype?
a. TtCc x ttCc
b. TtCc x TtCc
c. TtCc x ttcc
d. TTCc x ttCc
e. TTCc x TtCC
8. In humans, the allele for albinism is recessive to the allele for normal skin pigmentation.
a. If two heterozygous parents have children, what is the chance that the child will be
albino? __________________________
b. If the child is normal, what is the chance that it is a carrier (heterozygous) for the
albino allele? __________________________
c. If normal parents have an albino child, what is the probability that their next child will
be normal for pigment? __________________________
9. A student has a penny, nickel, a dime, and a quarter. She flips them all simultaneously and
checks for head or tails.
a. What is the probability that all four coins will come up heads? ___________
b. She again flips all four coins. What is the probability that she will get four heads both
times? __________
10. What is the probability that, if three identical coins were flipped, all would end up heads?
___________ What is the probability that the three coins would not either be all heads or all
tails?
___________
11. Flower position, stem length, and seed shape were three characters that Mendel studied. Each
is controlled by an independently assorting gene and has dominant and recessive expression
as follows:
Character
Flower position
Stem length
Seed shape
Dominant
Axial (A )
Tall (T )
Round (R )
Recessive
Terminal (a )
Dwarf (t )
Wrinkled (r)
If a plant that is heterozygous for all three characters were allowed to self-fertilize, what
proportion of the offspring would be expected to be as follows: (Note - use the rules of
probability (and show your work) instead of huge Punnett squares)
a. homozygous for the three dominant traits __________
b. homozygous for the three recessive traits __________
c. heterozygous __________
d. homozygous for axial and tall, heterozygous for seed shape __________
12. What is the probability that each of the following pairs of parents will produce the indicated
offspring (assume independent assortment of all gene pairs)?
a. AABbCc x aabbcc ----> AaBbCc ____________________
b. AABbCc x AaBbCc -----> AAbbCC ____________________
c. AaBbCc x AaBbCc -----> AaBbCc ____________________
d. aaBbCC x AABbcc ----> AaBbCc ____________________
13. The genotype of F1 individuals in a tetrahybrid cross is AaBbCcDd. Assuming independent
assortment of these four genes, what are the probabilities that F2 offspring would have the
following genotypes?
a. aabbccdd ____________________
b. AaBbCcDd ____________________
c. AABBCCDD ____________________
d. AaBBccDd ____________________
e. AaBBCCdd ____________________
14. In a cross between a female AaBbccDdee and a male AabbCcDdee, what proportion of the
progeny will be the same phenotype as the female parent?
(Assume independent assortment of all genes and complete dominance).