Harder Punnett Square Practice
Directions: Answer each of the questions on a separate sheet of paper. Make sure and
include a key, parents crossed, punnett square, genotypic ratio and phenotypic ratio. If
there is question, be sure to answer it.
1. White color in guinea pigs is recessive to dark color. A white guinea pig is mated
with a heterozygous dark guinea pig. What is the probability that these guinea pigs will
have a dark colored offspring?
2. In Reebops (a made up creature) curly tail is dominant over straight tail. Two
heterozygous curly tailed reebops are mated. What is the probability of them having a
straight tailed offspring?
3. In parakeets, yellow/green feather coloring is dominant over blue/grey coloring.
However, the blue/grey parakeets are more popular as pets than the green/yellow
birds. A parakeet breeder mated a blue/grey bird with a heterozygous yellow/green
bird. What is the probability of getting a blue/grey bird?
4. In fruit flies, grey body color is dominant over black body color. A homozygous grey
male is crossed with a black female. What proportion of their offspring will be black?
5. Sickle-cell anemia is inherited as a recessive trait. A healthy male whose father had
the disease marries a woman who has sickle-cell anemia. She is pregnant with her first
child. Figure out the genotype of the man and find out the probability that the child will
have the disease?
6. A single gene controls pea plant flower color. Violet flower color is dominant and
white flower color is recessive. A heterozygous violet flowered plant is mated with a
white flowered plant. What is the probability of getting white flowered offspring?
7. In mice, black coat color is dominant and white coat color is recessive. Two
heterozygous black mice are mated. What percentage of the offspring will be black?
8. Mr. Krabbs and his wife recently had a Lil’Krabby, but it has not been a happy
occasion for them. Mrs. Krabbs has been upset since she first saw her new baby who
had short eyeballs. She claims that the hospital made a mistake and mixed up her baby
with someone else’s baby. Mr. Krabbs is homozygous for his tall eyeballs, while his wife
is heterozygous for her tall eyeballs. Did the hospital make a mistake?
9. Tay-Sach’s is a deadly disease caused by a recessive gene. A man and a woman both
have the disease in their family and come to you (because you are a genetic counselor)
to find out their chances of having a baby with the disease. You analyze their family
history and realize that they are both heterozygous. What is the likelihood of one of
their children inheriting the disease?
10. Cattle have three colors. Red coat, white coat and a roan coat which is a mix of red
and white hairs. A roan cow is mated with a white cow. What is the chance of
producing another roan cow?
11. When a black bird is crossed with a white bird all of its offspring are grey. Cross a
grey and white bird. What is the probability that the offspring will be white?
12. The savannah grasshopper is very large with red and yellow stripes. The gene for
body color is codominant. A male red-bodied grasshopper is mated with a red and
yellow bodied grasshopper. What is the chance of producing a red-bodied
grasshopper?
13. Patrick and SpongeBob love to catch jellyfish. Patrick captures a red one and
SpongeBob grabs himself a blue one. After the hunt, they bring the creatures home and
allow them to mate. These jellyfish show incomplete dominance for body color. What
is the probability of producing a purple jellyfish?
14. Two short-tailed cats are bred together. They produce three kittens with long tails,
five short tails and two without any tails. Next, because you’re feeling crazy you breed
one of the long tail cats with a stray cat without a tail. What is the probability that the
new baby kitty will have a long tail?
For the following questions, do not include the genotypic ratios
15. In fruit flies, body color is controlled one gene and a second gene controls wing
shape. Grey body color is dominant and black body color is recessive. Normal shaped
wings is dominant and shriveled up wings are recessive. Two flies that are
heterozygous for both traits are mated. What is the likelihood of getting a fly with a
black body and shriveled up wrings?
16. In pea plants, height and seed texture are controlled by 2 different genes. Tall plants
are dominant and short plants are recessive. Round seeds are dominant and wrinkled
seeds are recessive. A plant heterozygous for both traits is mated with a short, wrinkled
seed plant. What percentage of the offspring will be tall with wrinkled seeds?
17. Wolves are sometimes observed to have black coats and blue eyes. Normal coat
color is dominant to black and brown eyes are dominant to blue. Suppose the alpha
male and alpha female of a pack (these are the dominant individuals who do most of the
breeding) are black with blue eyes (for the male) and normal colored with brown eyes
(for the female). The female is also homozygous for coat color and heterozygous for eye
color.
18. 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 is dominant to the
preference for rotted meat and that the tendency to bury the meat shallow 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.
19. About 70% of the human population can enjoy the bitter taste of the chemical
phenylthiocarbamide (PTC). The ability to taste this chemical results from a dominant
allele and not being able to taste is the result of having two recessive alleles. Albinism is
also a trait controlled by one gene with normal skin color (pigment) being dominant
and lack of skin color (pigment) being recessive. A woman with normal skin color who
cannot taste PTC has a father who is an albino taster. She marries a homozygous man
with normal skin color that is a taster, but who has a mother that does not taste PTC.
20. In field mice there is a gene that controls fur color and another gene that controls
the size of teeth (long or short). Field mice are sometimes seen with white and brown
patches. One day, you receive a gift from your nice science teacher of a male and female
field mouse. The male is brown and homozygous dominant for long teeth and the white
female is heterozygous for long teeth. What is the probability that the offspring will
have brown and white fur with long teeth?
Super Challenge Question (This is optional and is not worth any points)
You are a world famous breeder of Insane Bunnies. In insane bunnies, red eyes are
dominant to blue eyes. The bunnies have also been seen with neon green and purple
spots. Along with these traits, there is a third gene that controls the size of their eyes
(small, medium and large). It’s the holiday season and everyone is demanding an
insane bunny for Lunar New Year. Looks like it’s time for you to produce a few rabbits.
You choose a red-eyed male, with neon green fur and small eyes that had a father with
blue eyes. It’s mated with a female that has blue eyes, neon green and purple spots and
large eyes. What is the chance that you will create an insane bunny that has red eyes,
neon green fur and medium sized eyes?