LC Biology - Dihybrid Crosses

Another 2 questions for tonight's homework

Question 1

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).

a. Possible genotypes for Black coat: ________ Chestnut coat: _______
b. Possible genotypes for Trotting gait: _________ Pacing gait: _________
c. Male genotype: _____________ Male possible gametes: _______________
d. Female genotype: ___________ Female possible gametes: ______________
e. Draw a punnet square
f. Genotypic Ratio:
g. Phenotypic Ratio:
h. What percentage of the offspring will exhibit both dominant traits? _______
i. What percentage of the offspring will be chestnut trotters? ______
j. What are the chances of having a chestnut horse that paces? __ in __

Question 2
(Remember co-dominace)

In shorthorn cattle, the polled condition is dominant over horned. Also, the
heterozygous condition (Rr) of red coat (R) and white coat (r) is roan, an example
of codominance. (The roan coat contains both red and white fur because neither
allele is dominant over the other). If a homozygous polled, white male is bred to a
horned, red female, what will be the appearance of the F1 generation?


a. Possible genotypes for Pulled condition: ________ Horned: _______
b. Possible genotypes for Red coat: _____ White Coat: _____ Roan Coat: _____
c. Male genotype: _____________ Male possible gametes: _______________
d. Female genotype: ___________ Female possible gametes: ______________
e. Draw a punnet square
f. Genotypic Ratio:
g. Phenotypic Ratio:
h. What percentage of the offspring will exhibit both dominant traits? _______
i. What percentage of the offspring will be roan? ______
j. What are the chances of having a horned, white cow? __ in __
k. If you bred two of the F1 generation, what percentage of the new offspring (F2
generation) will exhibit both dominant traits? _______
l. If you bred two of the F1 generation, what percentage of the new offspring (F2

generation) will be horned and have a roan coat? _______