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Biology I
PUNNETT SQUARES – MONOHYBRID PROBLEMS O’ FUN
Use your knowledge of Mendelian genetics to solve the following problems! Show all work
for full credit!!!
1. A pea plant with wrinkled pea pods (ww) is crossed with a pea plant with smooth pea pods
(Ww). Construct a punnett square to determine the possible offspring. NOTE: smooth (W)
is dominant over wrinkled (w).
2. Two dogs mate and have puppies. Oh how cute!! The male dog is heterozygous for black
fur (where black fur is dominant), while the female dog is white (the recessive trait). Use
the information to solve the following:
a. what are the possible genotypes of the offspring of the two dogs?
b. what is the ratio of possible phenotypes for the puppies?
c. what are the overall odds/chances of the two dogs producing a puppy that is
black?
d. what are the overall odds/chances of the two dogs producing a puppy that is
homozygous for the trait of black fur?
3. In guinea pigs, the allele for a rough coat (R) is dominant over the allele for a straight
furred, smooth coat (r). Suppose two pigs that are heterozygous for this trait mate and
have offspring.
a. What are the phenotypes of each parent?
b. Construct a punnett square to show the possible outcomes of the offspring.
c. What are the genotypic and phenotypic ratios for the results of this cross?
d. Now take two genotypically different, yet phenotypically identical children and
cross them. What are the results? Show in a punnett square below.
4. Suppose that you raised rabbits for a living. You know that a mating between a black
rabbit and a brown rabbit produced all black offspring. Propose a hypothesis to explain the
color of the offspring. What are the genotypes of the parents? BE CAREFUL! THINK
ABOUT THIS ONE!!!
5. Woodrats are medium sized rodents with lots of interesting behaviors. You may know of
them as packrats. Let's assume that the trait of bringing home shiny objects (H) is
controlled by a single locus gene and is dominant to the trait of carrying home only dull
objects (h). Suppose two heterozygous individuals are crossed. How many of each genotype
would be expected if only 4 offspring were produced? Show your work (and be able to
explain the results).
6. Saguaro cacti are very tall cylindrical plants that usually have two L-shaped arms, one on
each side. Suppose you lived in southern Arizona where the Saguaro cactus is common and
you happen to have one growing in your yard. Your Saguaro has two arms but one is longer
than the other. Now, assume that arm length in these cacti are controlled by a single gene
with arms of the same length (A) being dominant to arms of different lengths. What is the
genotype of your cactus? In addition, could one of the parents of your cactus have had a
phenotype with arms the same length? How/why? Also, suppose you cross your cactus with
that of your neighbor which has arms of the same length. Your great grandchildren (it takes
a Saguaro cactus a long time to mature) find that half of the resulting offspring have arms
the same length and half have arms of different lengths. What was the genotype of your
neighbor's cactus?
7. The common grackle is a species of robin-sized blackbirds that are fairly common (hence
the name) over most of the United States. Suppose that long tails (L) were dominant to
short tails in these birds. A female short-tailed grackle mates with a male long-tailed
grackle who had one parent with a long tail and one parent with a short tail. What is the
male's genotype? How many of each genotype will be found in the F1 generation (assume 4
offspring)? How many of each phenotype will be found in the F1 generation?
8. The ability to curl your tongue up on the sides (T, tongue rolling) is dominant to not being
able to roll your tongue. A woman who can roll her tongue marries a man who cannot. Their
first child has his father's phenotype. What are the genotypes of the mother, father, and
child? What is the probability that a second child won't be a tongue roller?