Practice Problems
SBI 3U: Test Review
Monohybrid Cross
 In humans, brown eyes (B) are dominant over blue eyes
(b). If a heterozygous brown-eyed man marries a
heterozygous brown eyed woman, what are the possible
genotypes and phenotypes for their offspring?
Monohybrid Cross
 Cystic fibrosis (CF) is an recessive genetic disorder. If a
man who is homozygous dominant marries a woman who
is a carrier for cystic fibrosis, what are the possible
genotypes and phenotypes for their offspring?
Monohybrid Cross
 Huntington’s Disease is a dominant genetic disorder. If a
man who is heterozygous for Huntington’s Disease,
marries a woman who is homozygous recessive, what
are the possible genotypes and phenotypes for their
offspring?
Di-hybrid Cross
 In horses, the coat color black is dominant (B) over
chestnut (b). The trotting gait is dominant (T) over the
pacing gait (t). If a homozygous black pacer is mated to
a homozygous chestnut, heterozygous trotter, what are
the possible genotypes and phenotypes for their
offspring?
Di-hybrid Cross
 In mice the ability to run normally is a dominant trait.
Mice with this trait are called running mice (R). The
recessive trait causes mice to run in circles. Mice with
this trait are called waltzing mice (r). Hair color is also
an inherited trait in mice. Black hair (B) is dominant
over brown hair (b).
 Cross a heterozygous running heterozygous black mouse
with a homozygous running, homozygous black mouse.
What are the expected phenotypes and genotypes of
their offspring?
Incomplete Dominance
 In Mountain Mice, the tail length trait exhibits
incomplete dominance. What are the possible genotypes
and phenotypes from a cross between a homozygous
long tailed and homozygous short tailed mountain
boomer?
Co-dominance
 In dogs, gum coloration is co-dominant. A dog can have
pink gums, black gums, or pink with black spots. What
are the possible genotypes and phenotypes when a dog
with pink gums is bred with a pink and black spotted
gum dog?
Co-dominance
 In shorthorn cattle, hair colour is decided by codominant traits. If a cow that has red hair is bred with a
white hair cow, they produce roan offspring (both red
and white hairs). What would the expected genotypes
and phenotypes be when two roan cows mate?
Sex-linked Inheritance
 Hemophilia is an X-linked recessive genetic disorder. A
man who has hemophilia marries a woman who is
homozygous dominant for the trait. What are the
possible genotypes and phenotypes for their offspring?
Sex-linked Inheritance
 Male patterned baldness is an X-linked recessive genetic
trait. A bald man marries a woman who is a carrier for
the trait. They find out they are having a baby girl.
What is the probability that their daughter will go bald?
Multiple Alleles
 A woman with heterozygous blood type A marries a man
with blood type O. What are the possible genotypes and
phenotypes of their offspring?
Multiple Alleles
 A man with blood type AB marries a woman with blood
type B. What are the possible genotypes and phenotypes
of their offspring?