Download Genetics Practice Problems

Honors Biology Basic Genetics Practice Problems (just practice, no credit)
Monohybrid Crosses:
1. In a certain breed of dog, black coat color is dominant to brown coat color. If a male heterozygous
black dog is mated with a brown dog, what is the chance that the offspring will have brown coats?
2. Polydactyl, a condition where a person has 6 fingers and toes, is a dominant condition. A male with
6 fingers and toes marries a female with 6 fingers and toes. Is there any chance they could have a
child with 5 fingers and toes? Explain by showing work.
3. Assume brown eyes are dominant to blue eyes. Two heterozygous brown-eyed people mate.
Predict the genotypic and phenotypic ratios of their offspring.
4. Round seeds are dominant to wrinkled seeds. What percentage of the offspring will be round if a
heterozygote is crossed with a homozygous recessive? If two heterozygotes are crossed? If a
homozygous round is crossed with a heterozygote? If a homozygous round is crossed with a
homozygous wrinkled?
5. Two black dogs of the same breed as question 1 are mated many times. Out of 100 offspring, 25 of
them have brown hair. What are the genotypes of the parents?
6. A tall plant of unknown genotype is test-crossed. Of the offspring, 869 are dwarf and 912 are tall.
What is the genotype of the unknown parent? Show the cross to prove it.
7. Tongue rolling is a dominant trait; those with the recessive condition cannot roll their tongues.
Kanye can roll his tongue, but his mother could not. Kim cannot roll her tongue. What is the
probability that North will not be able to roll her tongue?
8. In goats, a recessive gene causes the goats to “faint” when they are startled. A farmer breeds two
goats (that have never fainted) and their first offspring faints two days after its birth. What must the
parent’s genotypes have been? Show the cross to prove it.
Dihybrid Crosses:
9. In pea plants, purple flowers are dominant to white flowers and tall plants are dominant to short.
Suppose you are a botanist working with pea plants. You cross a flower that is heterozygous for
purple flowers and tall plants with a short, white flowered plant. What is the percentage of
genotypes and phenotypes expected from this cross?
10. The normal fur color for wolves is brown (N) and is dominant to black (n). Brown eyes (B) are
dominant to blue (b). Suppose the alpha male is black with blue eyes and the alpha female is black
with heterozygous brown eyes. How many of the offspring (assume 16) living in the pack will have
each possible genotype?
11. Carrion beetles lay their eggs in dead animals and then bury them in the ground until they hatch.
Assume that the preference for fresh meat (F) is dominant to the preference for rotted meat and
that the tendency to bury the meat shallow (S) is dominant to the tendency to bury the meat deep.
Suppose a female carrion beetle homozygous dominant for both traits mates with a male
homozygous recessive for both traits. What will be the genotype of the F1 generation?
12. In guinea pigs, short hair is dominant to long hair. Also in guinea pigs, black eyes are dominant to
red eyes. A male guinea pig that is heterozygous for hair and recessive for eyes is crossed with a
female that is recessive for hair and heterozygous for eyes. What are the expected phenotypes of
their offspring and in what proportion?
13. The same male guinea pig is then crossed with a female who is heterozygous for both. What are the
expected genotypes and phenotypes of their offspring and in what ratios?
Probability:
14. Assume a male has the following alleles on his chromosome: AaBBccDdEE
What are the possible combination of alleles in his gametes? Which of Mendel’s Laws explains this?
What process separates alleles into gametes?
15. An organism with the genotype AaBbCCdd is crossed with one that is AAbbccDd. What are the odds
of having an offspring with the genotype AabbCcDd? In this problem, do not use Punnet squares.
Solve the problem using math and statistics and make sure you show all work.
16. What gametes can be produced from an individual with the genotype AaBbCCddEe?
Non-Mendelian Genetics:
17. In northeast Kansas there is a creature known as a wildcat. It comes in three colors, blue, red, and
purple. This trait is controlled by a single locus gene with incomplete dominance. A homozygous
(BB) individual is blue, a homozygous (bb) individual is red, and a heterozygous (Bb) individual is
purple. What would be the genotypes and phenotypes of the offspring if a blue wildcat were
crossed with a red one?
18. Suppose you have two rose plants, both with pink flowers. You cross the two plants and are
surprised to find that, while most of the offspring are pink, some are red and some are white. You
decide that you like the red flowers and would like to make more. What cross would you perform to
produce the most red flowered plants?
19. In a certain cactus, prickly spines can be two-pronged or one-pronged. If a true breeding onepronged cactus is crossed with a true breeding two-pronged cactus, the F1 generation has a mixture
of spines, some are two-pronged, some are one-pronged.
a. Is this an example of codominance or incomplete dominance?
b. Show the F2 generation (a cross between the two F1’s). What are the expected
phenotypes of the offspring and in what proportion?
20. In mice, the spinning behavior is caused by a dominant gene that affects the mouse’s equilibrium.
The gene is lethal if two alleles are present. Two “spinning mice” are mated together. Show the
cross. What are the phenotypes of the offspring and in what proportion?
21. A Nurse at a hospital removed the writs tags of three babies in the maternity ward. She needs to
figure out which baby belongs to which parents, so she checks their blood types. Using the chart
below, match the baby to its correct parents. Show the crosses to prove your choices.
Mr. Hartzel = O, Mrs. Hartzel = A
Jennifer = O
Mr. Simon = AB, Mrs. Simon = AB
Rebecca = A
Mr. Peach = O, Mrs. Peach = O
Holly = B
22. A child has type A blood. What are ALL the possible blood types of its parents? Show each cross to
prove that it is possible.
Sex-Linked Traits:
23. In fruit flies, eye color is sex linked. Red eyes are dominant to white eyes. A male with red eyes
mates with a female with white eyes. What will be the genotypic and phenotypic ratios of their
offspring?
24. The bison herd on Konza Prairie has begun to show a genetic defect. Some of the males have a
conditions know as “rabbit hock” in which the knee of the back leg is malformed slightly. It is a sexlinked recessive gene. Now, suppose that the herd bull who is normal (XN) mates with a cow that is
a carrier for rabbit hock. What are his chances of producing a normal son?
25. A rancher owns a bull with many desirable characteristics. Unfortunately, he also has a sex-linked
trait that in the recessive form leads to no pigment formation in the iris of the eye. This makes the
bull very sensitive to sunlight and could lead to blindness. The rancher wishes to breed him to a cow
that will minimize the chances of any offspring showing this trait. She would especially like to
produce another bull with most of his sire’s desirable qualities but without the nonpigmented eye.
Two cows with the dominant normal colored eyes (XN) are available that have been genetically
typed for this particular trait. Cow 1 has a genotype of XNXN and Cow 2 is XNXn. Which of these two
cows should the rancher choose as a mate to her bull if she wishes to minimize the occurrence of
the nonpigmented eye in his offspring? Why?