Name:
KEY
Hour:
Date:
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/21 Points
For ALL practice problems in this packet, remember to:
1. list trait and alleles
2. create a key
3. list the parents being crossed (P1)
4. form the Punnett square
5. determine genotypic ratio
6. determine phenotypic ratio
1. In dogs, black hair is dominant to brown hair. Cross a heterozygous black colored dog with a
brown dog. Determine the possible genotypes and phenotypes of the offspring.
Trait:
Key:
Hair color
HH =
Hh =
hh
=
Black
Black
Brown
(H,h)
P1:
Hh
H
Hh
Hh
h
h
Genotype:
2 Hh : 2 hh
Phenotype:
2 Black: 2 Brown
x
hh
h
hh
hh
2. In birds, long beaks are dominant to short beaks. Cross two birds heterozygous for beak
length. Determine the possible genotypes and phenotypes of the offspring. Be sure to
follow the same format as the problem above.
Trait:
Key:
Beak length
BB = Long
Bb = Long
bb = Short
Genotype: 1BB : 2 Bb : 1 bb
Phenotype: 3 Long : 1 Short
(B,b)
P1:
B
b
Bb
B
BB
Bb
LZHS Prentice Hall Biology – Genetics Practice Problems Key
Biology I
x
Bb
b
Bb
bb
1
Remember: With Incomplete Dominance- neither allele is dominant! There is an intermediate trait!
- 3 completely different phenotypes are possible
- the 3rd is intermediate to the other two (not blending)
1. In northeast Kansas there is a creature known as a wildcat. The fur color of this particular
wildcat exhibits incomplete dominance. There are three possible fur colors: blue, red, and
when alleles are mixed, purple. What would the possible genotypes and phenotypes of the
offspring be if a blue wildcat were crossed with a red wildcat?
Trait:
Key:
Fur Color
RR
Rr
rr
=
=
=
(R,r)
Blue
Purple
Red
P1:
Genotype:
4 Rr
Phenotype:
4 Purple Wildcats
RR
x
rr
R
Rr
Rr
r
r
R
Rr
Rr
2. The lubber grasshopper is a very large grasshopper, and is black in color with stripes. The color
of the stripes exhibit incomplete dominance. Red stripes or Yellow stripes may be expressed;
however, when alleles are mixed, orange stripes are expressed. What will be the genotypic and
phenotypic ratios of the F1 generation be as a result of a cross between two grasshoppers, both
with orange stripes?
Trait:
Key:
Genotype:
Stripe Color
GG
Gg
gg
=
=
=
(G,g)
Red
Orange
Yellow
1 GG : 2 Gg : 1 gg
P1:
Gg
x
G
g
Gg
G
GG
Gg
g
Gg
gg
Phenotype: 1 Red: 2 Orange: 1 Yellow
LZHS Prentice Hall Biology – Genetics Practice Problems Key
Biology I
2
1. In fish, the alleles for scale color show co-dominance. Scale color may be orange or white in
fish, however, when alleles are mixed scales will have orange and white stripes. If an orange
fish is crossed with a white fish, the following genotypes and phenotypes may be determined
regarding the possible offspring.
Trait: Scale Color
Key:
RR
Rr
rr
(R, r)
=
orange scales
= orange & white spots
=
white scales
P1:
RR
r
r
x
rr
R
Rr
Rr
R
Rr
Rr
Punnett Square:
Genotype: (letters)
4 Rr
Phenotype: (words) 4 (All) orange & white stripes
2. In fish, the alleles for scale color show co-dominance. Fish can have scales that are blue or
yellow, however, when alleles are mixed a fish with both blue and yellow scales results. If two
heterozygous fish are crossed, what are the genotypes and phenotypes of the possible
offspring?
Trait: Scale Color
Key:
BB
Bb
bb
=
=
=
(B, b)
Blue
Blue & yellow
Yellow
P1:
Bb
x
LZHS Prentice Hall Biology – Genetics Practice Problems Key
Biology I
Bb
3
Punnett Square:
B
b
B
BB
Bb
b
Bb
bb
Genotype: (letters) 1 BB : 2 Bb : 1 bb
Phenotype: (words) 1 Blue : 2 Blue & Yellow : 1 Yellow
LZHS Prentice Hall Biology – Genetics Practice Problems Key
Biology I
4
Key:
Phenotype
Light brown rabbit
Gray rabbit
Albino rabbit with black spots
Albino rabbit
Genotype
AA, AaB, Aab, Aa
aBaB, aBab, aBa
abab, aba
aa
1. Cross a heterozygous Albino rabbit with black spots and a homozygous gray rabbit. What are
the possible genotypes and phenotypes of the offspring?
Key: See Above
P1:
aba
x
aBaB
Genotype:
2 aB ab : 2 aBa
Phenotype:
4 gray
aB
aB
ab
aB ab
aB ab
a
aBa
aBa
2. What are the possible genotypes and phenotypes of the offspring for a cross between an Albino
rabbit with black spots that is homozygous with an Albino rabbit? Be sure to follow the same
format as the previous problem.
Key: See Above
P1:
abab
x
aa
ab
ab
Genotype:
4 a ab
Phenotype:
4 albino rabbits w/ black spots
LZHS Prentice Hall Biology – Genetics Practice Problems Key
Biology I
a
a ab
a ab
a
a ab
a ab
5
= female
= male
Use the following information for questions 1 & 2. In fruit flies, eye color is sex-linked.
Normal eye color is red, and recessive eye color is white.
Key:
XRXR
= female, normal, red
XRY
= male, normal, red
XRXr
= female, carrier, red
XrXr
= female, mutant, white
XrY
Xr
Xr
XR XRXr XRXr
Y X rY X rY
1. Cross a white-eyed female fly with a normal male fly.
Key: See Above
P1:
XrXr
X
Phenotype:
2.
XRY
2 XRXr : 2 XrY
Genotype:
2 carrier, females, red : 2 mutant, males, white
Cross a carrier female with a white-eyed male.
Key: See Above
P1:
XRXr
Genotype:
= male, mutant, white
X
XrY
1 XRXr : 1 XrXr : 1 XRY : 1 Xr Y
XR
Xr
Xr XRXr Xr Xr
Y XRY XrY
Phenotype: 1carrier, female, red : 1mutant, female, white: 1normal, male, red : 1mutant, male, white
Use the following information for question 3. In humans, colorblindness is sex-linked and
recessive. (Remember, that means males only need one recessive to become colorblind.)
Key:
XRXR= female, normal vision
XRY= male, normal vision
XRXr= female, carrier, normal vision
XrY= male, mutant, colorblind
XrXr= female, mutant, colorblind
3. Cross a normal female with a colorblind male.
Key: See Above
P1:
XRXR
X
XrY
XR
XR
Xr XRXr XRXr
Y XRY XRY
Genotype:
2 XRXr : 2 XRY
Phenotype:
2 carrier, normal vision, females : 2 normal vision, males
LZHS Prentice Hall Biology – Genetics Practice Problems Key
Biology I
6
1. In rabbits, long hair is dominant to short hair AND blue eyes are dominant to brown. Cross a
short haired, heterozygous blue eyed rabbit, with a homozygous long haired, brown-eyed rabbit.
Determine the possible genotypes and phenotypes of the offspring.
Traits:
Key: HH
Hh
hh
EE
Ee
ee
Hair Length
Eye Color
=
Long
=
Long
=
Short
=
Blue
=
Blue
=
Brown
(H,h)
(E,e)
P1:
H
H
H
H
e
e
e
e
Genotype:
8 HhEe : 8 Hhee
Phenotype:
8 Long Blue: 8 Long Brown
hhEe
h E
HhEe
HhEe
HhEe
HhEe
x
h e
Hhee
Hhee
Hhee
Hhee
HHee
h E
HhEe
HhEe
HhEe
HhEe
h e
Hhee
Hhee
Hhee
Hhee
2. In dorks, thick glasses are dominant to thin glasses and pocket protectors are dominant to
pencil cases. These two traits are being studied together. Cross a homozygous thick-glassed
dork that has a pencil case with a dork that is heterozygous for both traits. Determine the
possible genotypes and phenotypes of the offspring. Be sure to follow the same format as the
previous problems.
Traits: Glasses
(G,g)
P1:
GGrr
x
GgRr
Carriers
(R,r)
Key:
GG = Thick
Gg = Thick
gg = Thin
RR = Pocket Protector
Rr = Pocket Protector
rr = Pencil Case
G r
G R GGRr
G r GGrr
g R GgRr
g r Ggrr
G r
GGRr
GGrr
GgRr
Ggrr
G r
GGRr
GGrr
GgRr
Ggrr
Genotype:
4 GGRr : 4 GGrr : 4 GgRr : 4 Ggrr
Phenotype:
8 Thick glasses, Pocket Protector : 8 Thick glasses, Pencil Case
LZHS Prentice Hall Biology – Genetics Practice Problems Key
Biology I
G r
GGRr
GGrr
GgRr
Ggrr
7
You are now to create your own Di-hybrid cross. You must include two traits. However, the trait
you select may be expressed in any of the ways learned in this chapter. For example, you may
select one of your traits to exhibit complete dominance, while the other is incomplete or maybe
even co-dominant. Once you have completed the creation of your problem, you must have a
classmate attempt to solve the problem. You must then check the problem for errors and show
your classmate how they did and teach them how to correct it if they made a mistake. Good luck
and have fun! (Make sure to be school appropriate when selecting your traits!)
Here are the lines for you to write the final draft of your problem. A great idea may be to
make a rough draft on a separate sheet of paper, including you working out the problem to
make sure it works first! 
Classmate’s Name:
Traits:
Key:
( , )
( , )
=
=
=
=
=
=
P1:
x
Genotype:
Phenotype:
LZHS Prentice Hall Biology – Genetics Practice Problems Key
Biology I
8