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

Genotypic Ratio:_____________

Phenotypic Ratio:_____________

2 : 2 : 0

4 : 0

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

Genotypic Ratio:_____________

Phenotypic Ratio:_____________

1 : 2 : 1

3 : 1

Word Problems

A = Axial flowers a = terminal flowers

Cross homozygous axial plant with a terminal plant.

__________ X _________ AA aa

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

Genotypic Ratio:_____________

Phenotypic Ratio:_____________

0 : 4 : 0

4 : 0

Word Problems

A = Axial flowers a = terminal flowers

Cross 2 plants that are heterozygous for axial flowers.

__________ X _________ Aa Aa

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

Genotypic Ratio:_____________

Phenotypic Ratio:_____________

1 : 2 : 1

3 : 1

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

G G

G gg

G g

g

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

G G

gg gg

g g

Parents Genotypes are….

Gg X gg