Download Punnett Square Problems

Honors Biology: Punnett Square Problems #2
Name
Date
Instructions: Use Punnett squares to answer the following questions, as you did with the previous
Punnett square worksheet (review that for help). Show your work.
1. In humans a gene may help determine if you have dimples; the dominant allele (D) produces
dimples, while the recessive allele (d) results in no dimples. Igor has dimples, but his mom does
not. He marries Brunhilda, who does not have dimples. What is the probability that their first born
child will have dimples? Use a Punnett square to support your answer. Note: there is evidence a
single gene plays a role in dimples, but this trait can be influenced by other genes and the
environment.
2. Gregor Mendel crossed two heterozygous purple-flowered pea plants with each other. If he got
448 pea plants as a result of this cross, how many were probably white-flowered? (Hint: do the
Punnett square and use the resulting phenotypic ratio to determine how many of 448 plants were
probably white-flowered).
3. In the peas with which Mendel experimented, purple flowers are dominant to white flowers (use P
and p), and yellow seeds are dominant to green seeds (use Y and y). Imagine a pea plant that
was heterozygous for purple flower and yellow seeds.
a. Record the plant’s genotype: ______________________
b. Record the four possibilities of allele combinations it could possibly pass down during
reproduction if the genes independently assorted. The first one is done for you.
__PY___
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c. Now imagine that these genes do not independently assort. List a set of possible allele
combinations and explain how you arrived at this answer. Hint: there should be less than 4.
(over)
What are ratios of phenotypes for the following crosses?
d. A purple-flowered yellow-seeded pea plant that is heterozygous for both traits and a
homozygous purple-flowered plant that is heterozygous for yellow-seeds are crossed.
Assume each trait sorts independently. Purple flowers are dominant to white flowers (use
P and p), and yellow seeds are dominant to green seeds (use Y and y).
e. Two heterozygous purple-flowered yellow-seeded plants are crossed (heterozygous for
both traits). Assume each trait sorts independently.