Monohybrid, Dihybrid and Test Cross Test
Name:_________________
1. What is the expected phenotypic ratio of the progeny of a test cross with a squirrel
that is heterozygous for 2 traits? (T-tall t-dwarf; B-black; b-brown). Show your work
with the aid of a Punnett square. [4]
2. In humans, albinism is recessive to normal pigmentation. Two of your parent’s
friends have normal pigmentation. They have a child who is albino and are expecting
a second child. Your friends tell you, “We know that our chances of having one
albino child is 1:4, so we are sure our next baby will not be albino.” How would you
respond? Using a specific example and visual information (perhaps a Punnett
Square), explain to your these people whether their reasoning is correct. [2]
3. In summer squash, white fruit color (W) is dominant over yellow fruit color (w). If a
squash plant homozygous for white is crossed with a plant homozygous for yellow,
what will the phenotypic and genotypic ratios be for:
a. the F1 generation? [2]
b. the F2 generation? [2]
c. What will the phenotypic and genotypic ratios of the offspring be if you
perform a testcross with the F1 generation? [6]
4. A Biology student uses the wording “heterozygous recessive” as part of a solution to
a complicated genetics question. What comment do you provide to help in compiling
the final answer? [1]
5. The chestnut coat color of horses is due to a recessive gene, while the dominant allele
results in black. The pacing gait is due to a recessive gene, whereas the dominant
allele results in the trotting gait. Show the types of offspring that could result from a
cross of a black trotter (male), heterozygous for both genes, with a chestnut pacer
(female). Generate a Punnett square for this cross to help you answer the following
questions:
a. Possible genotypes for Black coat: ________[1] Chestnut coat: _________[1]
b. Possible genotypes for Trotting gait: _________[1] Pacing gait: _________[1]
c. Male genotype: ____________[1] Male possible gametes: _____________[1]
d. Female genotype: __________[1] Female possible gametes: ____________[1]
e. Genotypic Ratio: [1]
f. Phenotypic Ratio: [1]
g. What percentage of the offspring will exhibit both dominant traits? ______ [1]
h. What percentage of the offspring will be chestnut trotters? ______[1]
i. What are the chances of having a chestnut horse that paces? __ in __ [1]