Genetics
Punnett Square Practice
Genetics Practice Problems
• 1. For each genotype below, indicate whether it is
heterozygous (Ht) or homozygous (Ho)
AA
Bb
Cc
DD
Ee
ff
Gg
HH
Ii
JJ
kk
LL
Mm
nn
oo
PP
• 2. For each of the genotypes below determine what
phenotypes would be possible.
Consider: Purple flowers are dominant to white flowers
(P) & Brown eyes are dominant to blue eyes (B)
PP __________
BB __________
Pp __________
Bb __________
PP __________
bb __________
#2 Continued
• Round seeds are dominant to wrinkled seeds (R).
Bobtails in cats are recessive (T).
RR __________
TT__________
Rr ___________
Tt __________
rr ___________
tt ___________
• 3. For each phenotype below, list the genotypes
(remember to use the letter of the dominant trait)
Straight hair is dominant to curly hair (S).
________ straight
________ straight
________ curly
Pointed heads are dominant to round heads (H).
________ pointed
________ pointed
________ round
PUNNETT SQUARES
Crosses Involving One Trait
• In a certain species of animal, black fur (B) is dominant over
brown fur (b). Using a Punnett square, predict the genotypes
and phenotypes of the offspring whose parents are both Bb,
having heterozygous black fur.
Genotypes:
___% homozygous black fur (BB)
__ % heterozygous black fur (Bb)
___% homozygous brown fur (bb)
Phenotypes: ___% black fur
___ % brown fur
Now do the same when:
• One parent is homozygous black and the other is homozygous
brown.
Genotypes: ___% homozygous black fur (BB)
___ heterozygous black fur (Bb)
___% homozygous brown fur (bb)
Phenotypes
___% black fur
___% brown fur
Repeat this process again when
One parent is heterozygous black and the other is
homozygous brown.
Genotypes:
___% homozygous black fur (BB)
___ heterozygous black fur (Bb)
___% homozygous brown fur (bb)
Phenotypes
___% black fur
___% brown fur
Set up a Punnet square for each of the
following crosses.
Round seeds are dominant to wrinkled seeds
1. (Rf x rr).
What percent of these offspring will be round?
2. RR x rr
What percent of these offspring will be round?
3. RR x Rr
What percent of these offspring will be round?
4. Rr x Rr
What percent of these offspring will be round?
5. A (tall) TT plant is crossed with a (short plant) tt.
What percent of the offspring will be tall?
6. A Tt plant is crossed with a Tt plant. What percent of
the offspring will be short?
7. A heterozygous round seeded plant (Rr) is crossed
with a homozygous round seeded plant (RR). What
percent of the offspring will be homozygous (RR)?
8. A homozygous round seeded plant is crossed with a
homozygous wrinkled seeded plant.
What are the genotypes of the parents?
_____________ x ______________
What percent of the offspring will also be
homozygous?
9. In pea plants purple flowers are dominant to white
flowers. If two white flowered plants are cross,
What percentage of their offspring will be white
flowered?
10. A white flowered plant is crossed with a
plant that is heterozygous for the trait.
What percentage of the offspring will have
purple flowers?
11. Two plants, both heterozygous for the gene
that controls flower color are crossed.
What percentage of their offspring will have
purple flowers?
What percentage will have white flowers?
12. In guinea pigs, the alleles for short hair are
dominant.
What genotype would a heterozygous short
haired guinea pig have?
What genotype would a purebred, short haired
guinea pig have?
What genotype would a long haired guinea pig
have?
13. Show the cross for a pure breed, short haired
guinea pig and a long haired guinea pig.
What percentage of the offspring will have short
hair?
14. Show, the cross for two heterozygous guinea
pigs.
What percentage of the offspring will have short
hair?
What percentage of the offspring will have long
hair?
15. Two short haired guinea pigs are mated several
times. Out of 100 offspring, 25 of them have
long hair.
What are the probable genotypes of the parents?
_________ x
Show the cross to prove it!
Dragon Genetics
• Remember:
– UPPER CASE LETTERS REPRESENT
DOMINANT ALLELES
– AND
– Lower case letters represent recessive
alleles
Dragon Genetics, cont.
N = LONG NECK
N = short neck
E = RED EYES
e = white eyes
H = HORN PRESENT
h = horn absent
F = FIRE BREATHING
f = not fire breathing
G = GREEN BODY
G = grey body
L = LONG TAIL
l = short tail
S = SPIKES ON TAIL
S = no spikes on tail
R = RED WINGS
r = yellow wings
T = THREE TOES
t = four toes
W = YELLLOW BELLY
w = white belly
B = BLACK TAIL SPIKES
b= red tail spikes
K = FRECKLES
k = no freckles
X = X = NO EAR FRILLS
XX = FEMALE
Y = EAR FRILLS
YY = MALE
Dragon Genetics Questions
Using the Dragon Code, answer the following
questions.
1. What letters are used to represent wing
color?
2. What letters are used to represent neck
length?
3. The letter “Y” is used as a symbol to
represent _____________________.
4. The letter “e” is used to represent ________.
REMEMBER:
– An upper case, or lower case letter, is used to
represent a dominant trait.
– A lower case, or small letter, is used to represent
a recessive trait.
– Dominant traits completely mask recessive traits
– Refer to the Dragon key to answer the following
questions.
5. List 6 dominant traits shown in the key.
6. List 6 recessive traits shown in the key.
7. Fill in the blanks
Traits
Genotype
Neck Size
NN or Nn
Phenotype
Neck Size
Short neck
Spikes on Tail
No spikes
Eye Color
EE
Horn (present or
absent)
Hh
Fire Breathing
______ or ______
Belly Color
WW or Ww
Color of Spikes
Tail Length
Breaths fire
Red
______ or ______
Long
10. Cross a male dragon with a short neck with a
female dragon that is purebred for a long
neck. Show percentages of offspring.
11. Cross a hybrid fire breathing dragon with a
homozygous recessive non-fire breathing
dragon. Show percentages of offspring.
Dihybrid Cross
• Example: cross between hair and eye color
heterozygous pea seeds.
B
b
E
e
= Black
= blonde
= Brown
= blue
BbEe x BbEe
BE Be bE be x BE Be bE be
possible gametes produced
Punnett Squares - Dihybrid Crosses
Involve the Cross of Two Traits
In a dihybrid cross, when two traits are considered, the
number of possible combination of the offspring increases.
Suppose that Black hair (B) is dominant over blonde hair (b)
and
Brown eyes (E) are dominant over blue eyes (e).
Whqt percent of offspring could be expected to have blonde
hair and blue eyes if;
1. The father has black- hair (heterozygous) and brown eyes
(heterozygous) and the mother has blonde hair and blue
eyes.
• Genotype of father— BbEe
• Genotype of mother— bbee
• Copy the following Punhett square, then, fill in the boxes.
Dihybrid Cross
Dihybrid Cross
_______/______:
__
_______/______:
__
_______/______:
__
_______/_______: __
_________ phenotypic ratio