Name: ____________________________________ Period: ____ Date: __ /__ / __
Punnett Square Problems 3
Probability and Test Cross: Show a Punnett square to support your answer when appropriate.
1. In garden peas, long stems (L) are dominant and short stems (l) are recessive. A long plant is
crossed with a homozygous short plant. This is a test cross to determine the genotype of the long
plant. If all of the offspring produced in this test cross are also long plants, what was the genotype
of the parental long stem plant?
Allele Identification
Punnett Square
Long stem Plant Genotype
Parent Identification
2. If a heterozygous long stem plant (L) is crossed with a homozygous recessive short stem plant (l),
what is the probability that their offspring will be short stemmed? You may report your answer in a
fraction or a percent.
Allele Identification
Punnett Square
Short Stemmed Offspring Probability
Parent Identification
3. In garden peas, inflated (I) pods are dominant to constricted pods (i). A plant that has inflated
pods is crossed with a plant that has constricted pods in a test cross. If all of the offspring
produced from this cross have inflated pods, what was the genotype of the parental plant with
inflated pods?
Allele Identification
Punnett Square
Inflated Pods Parent Genotype
Parent Identification
4. A heterozygous inflated pod plant is crossed with a homozygous inflated pod plant. What is the
probability that their offspring will have inflated pods?
Allele Identification
Punnett Square
Inflated Pods Offspring Probability
Parent Identification
5. In garden peas, axial flowers are dominant and terminal flowers are recessive. In a cross
between two homozygous plants, one that has axial flowers and one that has terminal flowers,
what will be the probability that they produce an axial offspring then a terminal offspring?
Allele Identification
Parent Identification
Punnett Square
Probability of Producing an Axial
Offspring followed by a Terminal
Offspring
Name: ____________________________________ Period: ____ Date: __ /__ / __
Punnett Square Problems 4
Probability and Test Cross: Show a Punnett square to support your answer when appropriate.
6. The ability to roll your tongue is a dominant gene. If your mom is unable to roll her tongue, but
your dad is heterozygous for the trait, what is the probability that any new child they have will be
unable to be roll his or her tongue? You may report the answer as a fraction or a percent?
Allele Identification
Punnett Square
New Child Unable to Tongue Roll
Probability
Parent Identification
7. In horses a brown coat is dominant to a white coat. A heterozygous brown coat horse is crossed
with a homozygous white horse. What is the probability that they will produce one brown horse
and one white horse?
Allele Identification
Punnett Square
Probability of Producing a Brown Horse
followed by a White Horse
Parent Identification
8. Pea plants having purple flowers is a dominant trait to pea plants with white flowers. A white plant
is crossed with a purple plant. Some of the F1 generation has purple flowers, while others have
white flowers. What is the genotype of the parental purple plant?
Allele Identification
Punnett Square
Purple Flowered Parent Genotype
Parent Identification
9. You know the phenotype of an organism by just viewing it. Why is it impossible to know the
genotype of all organisms by just observing their physical appearance?
10. Describe what you could do to figure out the genotype of an organism with a known phenotype.
Explain your answer without using a Punnett Square.