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Genetics Practice Problems
1. In Kingwood Texas, there is a creature known as a panther. It comes in three colors, yellow, green, and blue. This trait is controlled
by a single gene with incomplete dominance. A homozygous (YY) individual is yellow, a homozygous (BB) individual is blue, and a
heterozygous (YB) individual is forest green. What would be the genotypic and phenotypic ratios of the offspring if a yellow panther
were crossed with a blue one?
Key: Y= yellow B=blue YB= forest green
Y
Y
Cross: YY x BB
B
YB
YB
Phenotypic Probability: 100 % forest green
B
YB
YB
Genotypic Probability: 100 % YB
What type of inheritance is this? Incomplete dominance
2. Wolves are sometimes observed to have black coats and blue eyes. Assume that these traits are controlled by single genes that are
located on two different chromosomes. Assume further that normal coat color is dominant to black coat color and that brown eyes
are dominant to blue eyes. Suppose a male wolf with a black coat and blue eyes mates with a female wolf heterozygous for both
normal coat color and brown eyes. What would the resulting pack look like?
Key: N=normal coat
n= black coat
B=brown eyes
b=blue eyes
Cross: nnbb x NnBb
Gametes: parent 1- nb, nb, nb, nb parent 2- NB, Nb, nB, nb
nb
nb
nb
nb
NB
NnBn
(Normal coat brown eyes)
NnBn
(Normal coat brown eyes)
Nb
Nnbb
(Normal coat blue eyes)
Nnbb
(Normal coat blue eyes)
nB
nnBb
nb
nnbb
(Black coat brown eyes)
(black coat blue eyes)
nnBb
nnbb
(Black coat brown eyes)
(black coat blue eyes)
NnBn
Nnbb
nnBb
nnbb
(Normal coat brown eyes)
(Normal coat blue eyes)
(Black coat brown eyes)
(black coat blue eyes)
NnBn
(Normal coat brown eyes)
Nnbb
(Normal coat blue eyes)
nnBb
nnbb
(Black coat brown eyes)
(black coat blue eyes)
Phenotypic Probability: 4- Normal coat, brown eyes 4-Normal coat, black eyes 4-Black coat, brown eyes 4-Black coat, blue eyes
Genotypic Probability: 4- NnBn 4-Nnbb 4-nnBb 4-nnbb
3. There is a certain breed of cattle that has a red coat, and when bred with cattle with a white coat, they produce roan (red
and white haired) offspring.
a. What type of inheritance is this? Codominance
b. If two roan cattle are crossed, what is the probability of red, white, and roan colors in their offspring?
Key: R= red coat W= White coat RW= Roan coat (red and white)
Cross: RW x RW
R
W
Phenotypic Probability: ¼ Red, ½ Roan, ¼ white
R
RR
RW
Genotypic Probability: ¼ RR, ½ RW, ¼ WW
W
RW
WW
4. In Smileys, eye shape can be starred, circular, or a circle with a star. What type of inheritance is this? Codominance
Write the genotypes of the smileys below each picture.
Key: C= Circle eyes S= Star eyes
CS= Circle with a star
Genotype:
CC
SS
CS
a. Cross a star-eyed smiley and a circle eyed smiley and show their expected phenotypic and genotypic ratios.
Cross: SS x CC
Phenotypic Probability: 100 % Circle-star eyes
Genotypic Probability: 100% CS
S
S
C
CS
CS
C
CS
CS
b. Cross a circle-star eyed smiley with a circle eyed smiley.
Cross: CS x CC
Phenotypic Probability: ½ Circle eyes, ½ Circle-star eyes
Genotypic Probability: ½ CC ½ CS
C
S
C
CC
CS
C
CC
CS
5. In snapdragons, flower color is controlled by incomplete dominance. The two alleles are for red and white. The
heterozygous genotype has a pink phenotype.
Key: RR= red WW= white RW=pink OR
RR=red R’R’=white RR’= pink
a. If I cross two heterozygous snapdragons, what are the possible outcomes of the offspring?
Cross: RW x RW OR RR’ x RR’
R
W
R
RR
RW
W
RW
WW
R
R’
Phenotype Probability: 25% red, 25% white, 50% pink
b. If I have a white snapdragon, but want to make red offspring, what should I do?
R
RR
RR’
Cross it with a red snapdragon first, resulting in pink offspring, then cross the pink offspring with
each other or with a red offspring
R’
RR’
R’R’
R
R
W
RW
RW
W
RW
RW
c. What cross will produce the most pink-flowered plants? Show a Punnett square to support your answer!
Cross a white and red flower RR x WW= 100 % pink!!