Name_____________________________________________ Date______________ Hour_______ Table #____
Punnett Squares
A Punnett square is a chart which shows/predicts all possible gene combinations in a cross of parents
(whose genes are known). Punnett squares are named for an English geneticist, Reginald Punnett. He
discovered some basic principles of genetics. He worked with the feather color traits of chickens in order to
quickly separate male and female chickens.
In pea plants (which Gregor Mendel studied), tall pea plants are dominant over short pea plants. Using
Punnett squares, you can predict the genotypes and phenotypes of the offspring of a cross between
homozygous (pure) tall pea plant and a homozygous (pure) short pea plant.
Step 1: Designate letters which will represent the gene/traits. Capital letters represent dominant traits, and
lowercase letters represent recessive traits. T = tall t= short
Step 2: Write down the genotypes (genes) of each parent. These are often given to you or are easy to
determine. TT x tt or (tall) (short)—both homozygous pure
Step 3: List the genes that each parent can contribute
Parent 1
TT
T
Parent 2
tt
t
Step 4: Draw a Punnett square--- 4 small squares in the shape of a window. Write the possible gene(s) of one
parent across the top and the gene(s) of the other parent along the side of the Punnett square.
Step 5: Fill in each box of the Punnett square by transferring the letter
above and at the side of each box into the appropriate box. As a general
rule, the capital letter goes first and a lowercase letter follows.
Genotype Phenotype
TT
Tall
Tt
Tall
tt
short
Step 6: List the possible genotypes and phenotypes of the offspring for this cross.
Since the capital letter indicates a dominant gene, T (tall) is dominant over t (short).
Therefore, each of the offspring in this case will be tall.
Name_____________________________________________ Date______________ Hour_______ Table #____
Use Punnett squares to determine the answers to the following samples.
1. One cat carries heterozygous, long-haired traits (Ss), and its mate carries homozygous short-haired traits
(ss). Use the Punnett square to determine the probability of one of their offspring having long hair.
A. 100%
S
s
B. 25%
C. 75%
s
D. 50%
s
2. One flower is heterozygous red (Rr) and it is crossed with a homozygous white (rr) plant. Use the Punnett
square to determine the probability of one of their offspring having a red color.
A. 75%
B. 25%
C. 50 %
D. 100%
3. In certain species of plant, the color purple (P) is dominant to the color white (p). Use the Punnett square
to determine the probability of the offspring being purple if a pure purple plant is crossed with a pure white
plant.
A. 25%
B. 0 %
C. 100%
D. 75%
Name_____________________________________________ Date______________ Hour_______ Table #____
Trait Determination Practice
Should This Dog Be Called Spot?
Imagine this microscopic drama. A sex cell from a male dog joins with a sex cell from a female dog. Each dog’s
sex cell carries 39 chromosomes. The zygote which results contains 78 chromosomes. It receives a set of
chromosomes from each parent. Suppose you could look at one pair of the zygote’s chromosomes.
From the female dog
From the male dog
Each chromosome of the pair contains genes for the same traits. But one chromosome may have a dominant
gene and the other a recessive gene. Use the drawing and the chart to answer the questions.
1. Would the new puppy have a spotted coat? _________
Trait
Dominant Gene Recessive Gene
2. What would the puppy’s hair texture be? ____________
Hair Length
Long (L)
Short (l)
3. Would the puppy have curly or straight hair? _________
Hair Texture
Bristly (B)
Silky (b)
4. Would the puppy be a hybrid or purebred for hair
Hair curliness Curly (C)
Straight (c)
length? _______________
Coat pattern
Solid(s)
Spotted (S)
What color is the Pod?
Green (G) is the dominant color for pods of pea plants. Yellow (g) is recessive.
1. What are the phenotypes of the following genotypes?
a. GG________________________________________________________
b. Gg ________________________________________________________
c. gg ________________________________________________________
Name_____________________________________________ Date______________ Hour_______ Table #____
2. Fill in the Punnett squares below to show the outcomes of the crosses. Next to each genotype write the
correct phenotype.
a.
GG x Gg
c. Gg x Gg
b.
GG x gg
d.
Gg x gg
A Visit to Solaron
On an imaginary planet called Solaron, green skin is dominant over red skin.
1. a. If a hybrid green-skinned male married a hybrid green-skinned female,
what is the probability that they will have children with green skin?
b. What is the probability that their children will have red skin?
2. a. If a hybrid green-skinned male married a homozygous red-skinned
female. What is the probability that they will have children with green skin?
b. What is the probability that their children will have red skin?