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PUNNETT SQUARE
PRACTICE
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Instructions
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Today you will learn about Punnett Squares.
If you are not already viewing this in presentation
mode, please press the F5 key to start viewing it in
presentation mode so you can see how to do the
presentation.
A green pea plant (GG) is being crossed with a green pea plant (Gg) yellow is the
recessive color.
Parent 1
Parent 2
Parent 1 has a Genotype of GG and a Phenotype of Green.
Parent 2 has a Genotype of Gg and a Phenotype of Green.
This means G is dominant and will make a green phenotype if there is GG or Gg.
That means g is recessive and will make a yellow phenotype if there is gg.
We’re now going to predict what their children would be like.
To predict what a parent will produce, we use a Punnett Square, named after the
man who invented it.
A green pea plant (GG) is being crossed with a green pea plant (Gg) yellow is
the recessive color.
See how the GG from Parent 1
separates into each space.
Step 1 – Put the parents on the
outside of the Punnett Square
Notice how
the Gg from
Parent 2
separates into
each space.
To predict what a parent will produce, we use a Punnett Square, named after the
man who invented it.
A green pea plant (GG) is being crossed with a green pea plant (Gg) yellow is
the recessive color.
Step 1 – Put the parents on the
outside of the Punnett Square
Step 2 – Take one allele from
each parent and combine them in
each box.
Your Punnett Square is complete!
A green pea plant (GG) is being crossed with a green pea plant (Gg) yellow is the
recessive color.
Only
box is Gg,
which
Step one
3 – Figure
out the
probability of each Genotype
is
stillPhenotype.
dominant, but it is
and
This would be GG
heterozygous dominant. 13 out of the 4 boxes are
out of 4 boxes means it isGG, so that equals 75%
25%.
The Phenotype is
Green because it is GG
Calculate the percent outcome for Genotype
and describe the phenotype for each
combination.
Genetic
Combination
Genotype
Phenotype
Dominant
Homozygous
75%
Green
Dominant
Heterozygous
25%
Green
Recessive
homozygous
0%
Yellow
Now You Try!
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You will fill in the Punnett Square on each slide.
You will also figure out what percent of the boxes are:
 Dominant Homozygous (2 capital letters: GG)
 Dominant Heterozygous (1 capital, 1 lowercase: Gg)
 Recessive Homozygous (2 lowercase letters: gg)
Remember…
 4 out of 4 = 100%
 3 out of 4 = 75%
 2out of 4 = 50%
 1 out of 4 = 25%
Be careful with capitalization!
A green pea plant (Gg) is crossed with a yellow
pea plant (gg).
Calculate the percent outcome for Genotype
and describe the phenotype for each
combination.
Genetic
Combination
Dominant
Homozygous
Dominant
Heterozygous
Recessive
homozygous
Genotype
Phenotype
A tall plant (TT) is crossed with a tall plant (Tt).
Calculate the percent outcome for Genotype
and describe the phenotype for each
combination.
Genetic
Combination
Dominant
Homozygous
Dominant
Heterozygous
Recessive
homozygous
Genotype
Phenotype
A tall plant (Tt) is crossed with a short plant (tt).
Calculate the percent outcome for Genotype
and describe the phenotype for each
combination.
Genetic
Combination
Dominant
Homozygous
Dominant
Heterozygous
Recessive
homozygous
Genotype
Phenotype
A red flower (Rr) is crossed with a white flower
(rr).
Calculate the percent outcome for Genotype
and describe the phenotype for each
combination.
Genetic
Combination
Dominant
Homozygous
Dominant
Heterozygous
Recessive
homozygous
Genotype
Phenotype
A white flower (rr) is crossed with a white flower
(rr).
Calculate the percent outcome for Genotype
and describe the phenotype for each
combination.
Genetic
Combination
Dominant
Homozygous
Dominant
Heterozygous
Recessive
homozygous
Genotype
Phenotype
A black chicken (BB) is crossed with a black
chicken (BB).
Calculate the percent outcome for Genotype
and describe the phenotype for each
combination.
Genetic
Combination
Dominant
Homozygous
Dominant
Heterozygous
Recessive
homozygous
Genotype
Phenotype
Now for Something New
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Now we will take this one step further. You will have
to figure out what the parents’ alleles are based on
the description.
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Remember…
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Homozygous means two of the same
Heterozygous means two different
You can have dominant homozygous (2 capital letters: BB)
 You can have recessive homozygous (2 lowercase letters: bb)
 You can have dominant heterozygous (1 capital letter, 1
lowercase letter: Bb)
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A homozygous dominant brown mouse is crossed with a
heterozygous brown mouse (tan is the recessive color).
Genotype
Parent 1
Parent 2
Calculate the percent outcome for Genotype
and describe the phenotype for each
combination.
Genetic
Combination
Dominant
Homozygous
Dominant
Heterozygous
Recessive
homozygous
Genotype
Phenotype
Phenotype
Two heterozygous white (brown fur is recessive) rabbits
are crossed.
Genotype
Parent 1
Parent 2
Calculate the percent outcome for Genotype
and describe the phenotype for each
combination.
Genetic
Combination
Dominant
Homozygous
Dominant
Heterozygous
Recessive
homozygous
Genotype
Phenotype
Phenotype
Two heterozygous red flowers (white flowers are
recessive) are crossed.
Genotype
Parent 1
Parent 2
Calculate the percent outcome for Genotype
and describe the phenotype for each
combination.
Genetic
Combination
Dominant
Homozygous
Dominant
Heterozygous
Recessive
homozygous
Genotype
Phenotype
Phenotype
A heterozygous white rabbit is crossed with a
homozygous black rabbit.
Genotype
Parent 1
Parent 2
Calculate the percent outcome for Genotype
and describe the phenotype for each
combination.
Genetic
Combination
Dominant
Homozygous
Dominant
Heterozygous
Recessive
homozygous
Genotype
Phenotype
Phenotype