Genetics Review Problems
Monohybrid Cross
A male and female flamingo are deciding whether or not to have kids. The father knows that to be able to
balance (B) on one leg, a child must contain the dominant B allele in its genotype. He also knows that if a b is
inherited, the baby flamingo would be unbalanced (b) on one leg. If both parents are heterozygous, what is the
chance that they will have an “unbalanced” kid?
Genotypic Ratio: _____________________
Phenotypic Ratio: _____________________
Chance: ______
Dihybrid Cross
R = normal runner
B = Black hair
r = runs only in circles
b = brown hair
Cross a heterozygous normal running, heterozygous black mouse with a homozygous normal running,
homozygous black mouse.
a. Genotypes of parents __________ ____________
b. Possible genotypes.
c. Possible phenotypes.
Incomplete Dominance
In Japanese four-o’clocks, the gene for red flower color (R) is incompletely dominant over the white flower
color (W). If a red plant is crossed with a pink plant, what would be the genotypic ratio and phenotypic ratio?
a. Genotypic ratio: __________________
b. Phenotypic ratio: _________________
Codominance
In roan horses a pair of codominant alleles, D1 and D2 is known to be involved in this trait. Horses with the
D1D1 genotype are white colored, horses with the D1D2 genotype are white and black spotted, and horses
with the D2D2 genotype are black in color. For each situation what would be the genotypic ratio and
phenotypic ratio?
a) a white horse and a black horse
b) a black horse and a spotted horse
c) a white horse and a spotted horse
Multiple Alleles
If a man with blood type B (IBi), marries a woman with blood type AB (IAIB), what is the probability that their first
child will have blood type B?
a. What is the probability? ________
Sex-Linked Traits
1. Hemophilia is a blood disorder that prevents clotting. It is a recessive, sex-linked trait. If the mother is
a completely healthy for the disease and the father is a hemophiliac, complete the following questions:
a. Mom’s genotype =__________
b. Dad’s genotype =___________
c. Cross them and show their punnett square.
d. What is the probability that the child will NOT have hemophilia? _______
e. What is the probability that a child will be affected? _________
2. Hemophilia is a blood disorder that prevents clotting. It is a recessive, sex-linked trait. If the mother is
a carrier for the disease and the father is healthy, complete the following questions:
f. Mom’s genotype =__________
g. Dad’s genotype =___________
h. Cross them and show their punnett square.
i. What is the probability that the child will NOT have hemophilia? _______
j. What is the probability that a child will be affected? _________
k. Probability for an affected male? ________
l. Probability for an affected female? _________