Welcome!‎ > ‎Student Resources‎ > ‎

Mendelian Genetics and the Punnett Square

Jillian Schwenk

A4 Lesson Plan

Lesson Title:  Mendelian Genetics and the Punnett Square

Georgia GPS:  SB2

SB2 Students will analyze how biological traits are passed on to successive generations.

a. Distinguish between DNA and RNA.

b. Explain the role of DNA in storing and transmitting cellular information.

c. Using Mendel’s laws, explain the role of meiosis in reproductive variability.

d. Describe the relationships between changes in DNA and potential appearance of new traits including

Alterations during replication




Mutagenic factors that can alter DNA

High energy radiation (x-rays and ultraviolet)


e. Compare the advantages of sexual reproduction and asexual reproduction in different situations.

f. Examine the use of DNA technology in forensics, medicine, and agriculture.


Desired Learning Objectives: 

1.      At the end of the lesson, the learner will be able to recall who Gregor Mendel was and his importance to the field of genetics, when asked aloud by the teacher.

2.      At the end of the lesson, the learner will be able to define genetic terminology such as gene, allele, heterozygous, and homozygous, when given the term.

3.      At the end of the lesson, the learner will be able to assemble and evaluate a Punnett square and its outcome percentages, given a starting figure.

Purpose of Lesson:  To introduce the students to the history of genetics, Gregor Mendel, and the basics of genetics, using an internet resource.

Equipment Needed: Computer to access website; http://sites.google.com/site/schwenkscience/Home

Materials Needed:  Punnett Square worksheet (attached), paper, and writing utensil

Time Required:  90 minutes, one class period


Synopsis of Lesson:

Ask the students to read over the history of genetics and Gregor Mendel the night before class. Students are to go to Class webpage, Student Resources, and Click on “History of Genetics,” under “Links for Genetics, DNA & RNA.” When they come in for class, they should have somewhat of an idea about the basics of genetics. Develop a PowerPoint presentation with lots of graphics and visuals to explain the basic terms of genetics (gene, DNA, chromosome, trait, meiosis, allele, Punnett square, recessive, dominate, heterozygous, homozygous, etc.) Review who Gregor Mendel was and hold a class discussion on his importance to the field of genetics. Start by showing them how to fill out a Punnett square on the board. Discuss how this relates to Mendel’s experimentation with peas and flowers. Emphasize the predictable percentages that can be derived from a Punnett square. Pass out the Punnett square worksheet and have the students develop and fill in their own Punnett squares.

Assessment of Learners and Instruction:

Overall assessment can be measured as you let the students start to explore Punnett squares. How many students grasp the concept quickly? What areas seem to cause the most struggles for some? You can reiterate key points that may have escaped some students.

1.      Objective 1 can be assessed by having an open discussion about Gregor Mendel and the history of genetics. Pay attention to how many students seem eager to answer and how accurate and explicit their answers are.

2.      Objective 2 can be assessed by preparing a document with the basic genetic terms given, and then ask the students to provide the definition.

3.      Objective 3 can be assessed by providing blank Punnett square tables and reciting a scenario to the students (say, a cross between a heterozygous yellow pea plant, with a homozygous green pea plant), and then ask the students to fill in the Punnett square to represent the given scenario. You can then ask the students to provide the predicted outcome percentages.





Punnett Square










                   A = dominant allele;  a = recessive allele

                  AA=25%, Aa=50%, aa=25%, Total: 100%