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Punnett square worksheet
Complete the following monohybrid crosses: draw a Punnett square, list the ratio and describe the
offspring. Be sure to remember that the capital letter is dominant.
Example
A green pea plant (GG) is being crossed with a green pea plant (Gg).
G
G
GenoType=
G
GG
GG
g
Gg
Gg
1/2 GG: 1/2 Gg ; 0 gg
Phenotype= 100% Green pea plants: 0 other color
1) A green pea plant (Gg) is crossed with a yellow pea plant (gg).
2) A black chicken (BB) is crossed with a black chicken (BB).
3) A black chicken (Bb) is crossed with a black chicken (Bb). (b is the white allele)
4) A homozygous dominant brown mouse is crossed with a heterozygous brown mouse (tan is the
recessive color). T=brown, t=tan
5) Two heterozygous white (brown fur is recessive) rabbits are crossed.
6) Two heterozygous red flowers (white flowers are recessive) are crossed.
7) A heterozygous white rabbit is crossed with a homozygous brown rabbit.
8) Kathleen’s cat has kittens. The female cat is heterozygous for coat color and the male is also.
White coats are recessive. What are the chances they will have a female, white kitten?
9) For the peas Gregor Mendel worked with, purple flower color (P) is dominant over white flower
color (p). A purple-flowered plant is crossed with a white-flowered plant. 24 plants are grown
from the seeds from that mating. 12 of them are purple and 12 are white. What was the genotype
of the parent plants?
Complete the following crosses: draw a Punnett square, list the ratio and describe the offspring. These
crosses may represent codominance, sex-liked traits, incomplete dominance.
1.
In cows, the allele for red hair (HR) and the allele for white hair (HW) are codominant. The
heterozygous condition results in a mixture of red and white hairs and the cows are called roan. What
would occur if a red cow was crossed with a roan cow? Show the Punnett square as both the genotypic
and phenotypic ratios.
2.
Sickle cell anemia is a trait that exhibits incomplete dominance. A person with an AA genotype does
not have sickle cell anemia, and a person with an SS genotype has full sickle cell anemia. A person
with an AS genotype will have some sickle-cells, though s/he might show minimal or no symptoms (a
“carrier”).
Englebert is a carrier for sickle-cell anemia (he has the gene, but not the symptoms), and his wife,
Gwendoline, does not. What are the chances that Engelbert and Gwendoline will have a child with
ANY sickle-shaped blood cells? Show your work!
3.
Draw a Punnett square showing all the possible blood types for the offspring produced by a type “O”
mother and an a Type “AB” father
4.
Mrs. Clink is type “A” and Mr. Clink is type “O.” They have three children named Matthew, Mark,
and Luke. Mark is type “O,” Matthew is type “A,” and Luke is type “AB.” Based on this information:
a. Mr. Clink must have the genotype ______
b. Mrs. Clink must have the genotype ______ because ___________ has blood type ______
c. Which child can NOT be the offspring of these parents?
5.
In a species of Birds, incomplete dominance between alleles for black (B) and white(w) feathers is
observed. Heterozygotes are blue. If two blue birds are crossed, what will be the possible genotypes
and phenotypes of the offspring?
7. A tall, yellow-seeded pea plant heterozygous for height and seed color (TtYy) is crossed with a tall,
green-seeded pea plant that is heterozygous for height but homozygous recessive for seed color (Ttyy). If
80 offspring are produced, how many are expected to be tall and have yellow seeds?
8. Assume a male with type O blood mates with a female who has type A blood. The female’s mother had
type A blood and her father had type B. What is the probability that their first child will have type A blood?
What is the probability that their third child will have type O blood?
9. In humans, one of the genes determining color vision is located on the X chromosome.The dominant
form (C) produces normal color vision; red-green color blindness (c) is recessive.
If a man with normal color vision marries a color-blind woman, what is the probability of their having a
color-blind son?
A color-blind daughter?
10. In humans, normal color vision (XC) dominates red-green colorblindness (Xc). This is a sexlinked trait. Two parents produce daughters who are all carriers and sons who are all normal.
What are the probable genotypes of the parents?
11. In the couple described in the last problem, the woman gives birth to a color-blind but otherwise
normal daughter. The husband sues for a divorce on the grounds of adultery. Will his case stand
up in court? Explain.
12. In a species of Rabbit, the alleles for black (B) fur is dominant over, red fur (r), which is dominant
over yellow fur (y) , which is dominant over white fur (w). What will the possible genotypes and
phenotypes of the offspring be if a Black heterozygote (Bw) and a red heterozygote (ry) mated?
13. In the species of Rabbit above, a yellow rabbit and a red rabbit mate. 25% of their offspring are
white. What are the genotypes of the parents?