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.
Return to top of page
SPECIFIC OBJECTIVES
BACKGROUND
Return to top of page
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. |
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.)
Return to top of page
INTERACTIVE EXERCISES
Materials needed: One coin for each pair of students
1. Simple Probability.
Literature | |
Local Places to Visit | |
Web Sites | Simple Punnet Square |