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TITLE:  Genetics: Punnet Squares
Presented to grade level 7
 

GOALS
The purpose of this lesson is to demonstrate how Punnet Squares are used to investigate genetic crosses. This lesson also involves a review of probability and its importance in genetics, as well as a review of introductory genetics principles.
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SPECIFIC OBJECTIVES

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BACKGROUND
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SOLs COVERED
LS 14 The student will investigate and understand that organisms change over time.  The key concept included in this lesson is that genetic variation can lead to diversity of organisms. 
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DEMONSTRATIONS AND EXHIBITS
Materials needed:  coin, chalkboard, chalk

1. Probability.  Discuss probability using coin toss example.  Since there are only two options - heads and tails - on a single toss, there is a 50% chance that the coin will come up heads and a 50% chance that it will come up tails.  The coin will not "remember" what happened last time, so the outcome of each flip is independent of all previous outcomes.  (Go to interactive exercise.)

2.  Punnet Squares.  Choose an example of constructing a Punnet Square to show the students.  The illustration shows one parent homozygous for the AA allele and another that is heterozygous (Aa).  Point out that there are two ways to get AA and two to get Aa.  Overall, the average set of offspring for these parents should be 50% AA and 50% Aa.  This is a great place to discuss genotypes and phenotypes again, since in the illustrated example, the offspring will only show one phenotype even though two genotypes are present.  (Go to interactive exercise.)
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INTERACTIVE EXERCISES
Materials needed:  One coin for each pair of students
1. Simple Probability.

2. Constructing Punnet Squares.  Return to top of page
 

INTERESTING EXAMPLES

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OTHER RESOURCES
 
Literature
Local Places to Visit
Web Sites Simple Punnet Square

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last updated: March 10,  2000
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