Single-Factor Punnett
Square Notes
Punnett Square
A
diagram that can be
used to predict the gene
combinations that might
result from a cross
Basic Problems:
T = Tall
 t = short


Tt x TT
T
T
t
T
TT
TT
Tt
Tt
T
T
t
T
TT
TT
Tt
Tt
TT: Tt : tt
2 : 2 :0
Genotypic Ratio:_____________
4 : 0
Phenotypic Ratio:_____________
Basic Problems:
T = Tall
 t = short


Tt x Tt
T
T
t
t
TT
Tt
Tt
tt
T
T
t
t
TT
Tt
Tt
tt
TT: Tt : tt
1 : 2 :1
Genotypic Ratio:_____________
3 : 1
Phenotypic Ratio:_____________
Word Problems
A = Axial flowers
 a = terminal flowers



Cross homozygous axial plant with a
terminal plant.
AA
aa
__________
X _________
Basic Problems:
A = axial
 a = terminal


AA x aa
a
A
A
a
Aa
Aa
Aa
Aa
a
A
A
a
Aa
Aa
Aa
Aa
AA: Aa : aa
0 : 4 : 0
Genotypic Ratio:_____________
4 : 0
Phenotypic Ratio:_____________
Word Problems
A = Axial flowers
 a = terminal flowers



Cross 2 plants that are heterozygous for
axial flowers.
Aa
Aa
__________
X _________
Basic Problems:
A = axial
 a = terminal


Aa x Aa
A
A
a
a
AA
Aa
Aa
aa
A
A
a
a
AA
Aa
Aa
aa
AA: Aa : aa
1 : 2 : 1
Genotypic Ratio:_____________
3 : 1
Phenotypic Ratio:_____________
Backwards Problems
G = Green pods
 g = yellow pods


¾ of the plants produced by a cross
between 2 unknown pea plants have green
pods and ¼ have yellow pods. What are
the genotypes of the parent plants?

__________ X _________
G
G
G
gg
G
G
g
g
GG
Gg
Gg
gg
Parents Genotypes are….

Gg X Gg
Backwards Problems
G = Green pods
 g = yellow pods


What cross would result in ½ of the
offspring having green pods and ½ of the
offspring having yellow pods?

__________ X _________
G
G
gg
gg
g
G
g
g
Gg
Gg
gg
gg
Parents Genotypes are….

Gg X gg