This document explains how to use Punnett squares to predict genetic outcomes based on Mendel's laws of inheritance. It provides examples of setting up and interpreting Punnett squares to determine the probability of different traits being passed on from parents to offspring. Key points covered include dominant and recessive alleles, determining genotypes and phenotypes from Punnett squares, and calculating probability percentages. Practice questions are provided at the end for the reader to set up Punnett squares to predict genetic inheritance in different scenarios.

1. Punnett Squares
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2. Punnett Squares
• Using Mendel's laws and a punnett square, genetic
outcomes can be predicted.
pp (white flower) PP (purple flower)
The alleles
P P
The alleles from one
Fill in the
from one P p P p parent go on
p boxes with the
parent go top
P p P
alleles
p
on the side p Slide
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3. Interpreting Punnett Squares
Each box represents a
25% chance of
obtaining offspring with
that trait
If you cross PP with pp, you have a 100% chance of
offspring that are Pp
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4. Example:
• Predict the possibility of producing a white flower
pea plant if both parents have one dominant gene
and one recessive gene
P p
P PP Pp pp = white → 25%
p Pp pp
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5. Example:
• A father (Bb) has brown hair and the mother has
(bb) has blonde hair. Predict the possible
phenotypes of their children and include percent
probability.
B b
b Bb bb Brown hair → 50%
Blonde hair → 50%
b Bb bb
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6. Example:
• A dog with a long tail (TT) has puppies with a dog
that has a long tail (Tt). What is the probability
that they will produce a puppy with a short tail?
T T
T TT TT Short tail = tt and there
is zero probability.
t Tt Tt
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7. Practice Questions
Write the following questions in your copybook and
answer each using Punnett Squares.
1. What is the possibility of a man with freckles (FF) and a woman without
freckles (ff) producing a child without freckles?
2. A long haired guinea pig (Hh) and a short haired guinea pig (hh)
produce many offspring. What will be the genotypes and phenotypes of
the offspring (give percentages of each)?
3. A cricket with hairy legs (YY) and a cricket without hair on the legs have
offspring. What percentage of the offspring will have hair on their legs?
4. A giraffe with one dominant alleles for straight hair has offspring with a
giraffe with curly hair (aa). What is the probability of the offspring will
have curly hair?
5. Critical Thinking: In bats round ears (R) are dominant. A bat with round
ears and a bat with pointy ears have a baby. What are the possible
phenotypes and genotypes of the baby? (Hint: Since you don´t know
the round-ear bat´s genotype, you may have to do two Punnett Slide
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Squares).