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Punnett Square Problems
Monohybrid Problems
1. If a woman that is homozygous for NO widow’s peak has children with a man that is
heterozygous and DOES have a widow’s peak, what are the odds that their children will be
born with widow’s peaks?
2. KJ has dimples (dominant). Her dad does NOT. Her husband does NOT have dimples,
either. What are the odds that their daughter has dimples?
3.
Hitchhiker’s thumb is a recessive trait. What are the odds that a man
with hitchhiker’s thumb will have kids with thumbs like his if he marries a
woman who also has hitchhiker’s thumb?
4. What are the odds that a couple that are both heterozygous for “Long Second
Toe” will have a child whose second toe is short?
5. The gene for cleft (dimple) chins is dominant. John Travolta has a cleft (dimple) chin, but his
mother did not. His wife, Kelly Preston, does not have one either. What are the odds that
John and Kelly’s children will have cleft chins?
MULTIPLE ALLELE PROBLEMS
1.
If a man with blood type AB marries a woman heterozygous for type A, what is the
probability that their child will be type B?
2.
A mother has type A blood and a father has type B blood. If their baby has type O blood,
what is the genotype of the parents?
3.
Use a punnett square to show the possible genotypes and phenotypes for blood type of
the offspring of two parents, one with blood type O and one with blood type AB.
4.
Two women gave birth to girls in the same hospital at the same time. The nurses think
they may have accidentally switched the babies' name tags and given the babies to the wrong
parents. One baby, Jane, is type O. The other baby, Mary, is blood type A. The father in one set
of parents, the Reds, is blood type A, and the mother is type B. The father in the other set of
parents, the Greens, is blood type AB, and the mother is type O. Figure out which baby belongs
to which parents. Show your work and reasoning.
SEX-LINKED PROBLEMS
1.
Show, using a Punnett Square, how the sex of a child is determined. Does the egg from
the mother or the sperm from the father determine the sex of the offspring?
2.
Color blindness is a sex-linked recessive trait. What is the probability that a color blind
woman and a color-blind man will have: a. a normal sighted son b. a color blind daughter.
3.
What is the probability that two parents with normal color vision will have color blind
sons or daughters if the mother's father is color -blind?
4.
Hemophilia is a sex-lined blood disorder. People with this disease can bleed to death
from a small cut because their blood does not clot. It is caused by a recessive allele. You are a
normal (homozygous) female who is about to marry a hemophiliac male. What are your
chances of having a child with this blood disorder?
5.
In fruit flies (Drosophila), the gene for red eye color, R, is dominant to the gene for white
eye color, r. The trait is sex-linked. A red-eyed male was bred to a heterozygous red-eyed
female. Mark true/false.
a. The genes for eye color are carried on the X chromosome.
b. The male's genotype is XRYr.
c. The female's genotype is XRXr.
d. Half of the gametes produced by the female should contain Xr.
e. All the gametes produced by the male should contain Yr.
f. Of the offspring produced, all females are expected to have red eyes.
g. Of the offspring produced, all males are expected to have white eyes.
h. The offspring of a white-eyed male must have the genotype XrY.
i. Female offspring produced from this cross could have the genotype XrXr.
PEDIGREE PROBLEMS
1. Determine the genotypes of each of the following 12 individuals (color blindness is sexlinked)?
2.
The following is a pedigree of myopia (near-sightedness). This condition is caused by a
recessive gene, but is NOT sex linked. Determine whether the 8 individuals are A.
Heterozygous B. Homozygous C. Not enough sufficient data to determine genotype.
3.
Huntington’s Disease is caused by a dominant gene. (not sex linked) Based on the laws
of probability, what are the likely genotypes of the numbered individuals?
4.
This pedigree to the right shows the blood types of
some individuals. List all the possible genotypes of each
numbered individual.