# Probability Punnett Squares

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```							 PROBABILITY &
PUNNETT SQUARES

Mrs. Sinkaus
Fall 2008
BELL RINGER

What do these pictures show?
BELL RINGER CONT.

•The hand and foot
have six fingers and

•This is the result of
a genetic disorder
referred to as
Polydactyly –
having more than
five digits.
BELL RINGER CONT.

What religious group
do these people belong
to?

They are Amish - lead a
simple life centered on
family and religion. Large
population resides in
Lancaster County, PA.
BELL RINGER CONT.
The Amish live separately
from the rest of society.
They typically marry only
other Amish people.
What if I told you
Polydactyly is more
common among the
Amish than in the
general population. Why
do you think that is true?

Why might it someday be important for you
to know if you are a carrier for a genetic
disease?
OBJECTIVES
As a result of this lesson you (my students)
will be able to:

•Explain how geneticists use the principles of
probability
•Describe how geneticists use Punnet Squares
•Distinguish between the concepts heterozygous and
homozygous
•Solve genetic problems using a Punnet Square
•Explain the difference between probable genotypic
and phenotypic ratios and actual numbers of offspring
This lesson will address Science and
Technology PA Standards 3.3.10C, and
3.2.10C,D
WHAT IS PROBABILITY?

Probability is the likelihood
that a particular event will occur

Example: A coin flip

What are the possible outcomes
when you flip a coin?

Answer: There are two – it could
land heads up or tails up
WHAT IS PROBABILITY? CONT.
Probability is the likelihood
that a particular event will occur

Example: A coin flip

What are the chances a coin will

What are the chances a coin will
land tails up?

WHAT IS PROBABILITY? CONT.
If you flip a coin 3 times in a row, what
is the probability it will land heads up
every time?

Each coin flip is an
independent event – each time the
coin is flipped, the probability of it
landing heads up is ½ .
The probability of flipping 3 heads in a
row is:
½ x ½ x ½ = 1/8
Remember: Past outcomes do not
effect future outcomes!
HOW DOES PROBABILITY RELATE TO
GENETICS?
   The principles of probability can be used to
predict the outcomes of genetic crosses!

Coin Toss Lab
•   Work with a partner
•   Follow the instructions on this worksheet to
complete the Coin Toss Lab
COIN TOSS LAB DISCUSSION
probabilities?

   What did you notice as your number of tosses
increased?

closer your actual results should have been to
Probable outcomes are not always equal to
actual outcomes; however, the two should
get closer as the number of trials increases.
HOMEWORK REVIEW

When an organism has two identical alleles for a
particular trait (ex. TT or tt), it is said to be
_______.

When an organism has two different alleles for the
same trait (ex. Tt), it is said to be _________.
HOMEWORK REVIEW CONT.

This girl is displaying one of the traits from

What is her phenotype?
Answer: She has a Widow’s Peak

What is a possible genotype given that Widow’s
Peak is a dominant allele?
INTERACTIVE ACTIVITY

knowledge of genotype and
phenotype in this web lab!
PUNNETT SQUARES
Let’s combine our knowledge of probability with
our understanding of genotype and phenotype.

Click on the Punnett Square above to learn how to
use Punnett Squares to predict the genotypes
and phenotypes of offspring given the parents’
genotypes!
MORE PUNNETT SQUARES!
Work with a partner to complete this web lab on
Punnett Squares.

Click on the rooster below to enter the web lab!
CLOSURE
What is the genetic disorder that is
displayed in this picture?

Polydactyly is a dominant genetic
disorder. John is heterozygous for
Polydactyly – What is his genotype?

What is John’s phenotype?
Answer: He displays the symptoms of
the disorder – he has six toes.
CLOSURE CONT.
John (Pp) marries Diane who is
homozygous for Polydactyly. What
are the chances they will have a
child who is homozygous for
Polydactyly?
Use a Punnett Square to answer the
question!
CLOSURE CONT.
P      p
P   PP     Pp
P   PP     Pp
HOMEWORK

Click on Sponge Bob for a worksheet on
Bikini Bottom Genetics for more Punnett Square
practice!

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