Thanks to an experiment with peas, we can now use a bunch of letters to guess about how tall your kiddos will be using the Punnett Square!

This little box is a foundational genetic principle that helps scientists predict which traits an offspring can have.

Keep reading to glean a few tools to introduce this concept to your students, including a free printable!

Peas, the ABC's, and the Punnett Square...

DNA, Genes, and the Punnett Square

Let's start out with a bit about the genetic players - DNA and genes!

Coded within the DNA of an organism are thousands of genes. Each of these genes contains the code for certain characteristics. (Check out this LEGO DNA tower to understand how this coding works.)

These genes are passed down from the parents to the offspring. They come in pairs, called alleles, which are either dominant or recessive. The combination of these alleles determines which characteristic will be displayed.

Gregor Mendel, an Austrian monk, discovered this principle as he conducted an experiment with peas in the 1860s. He observed that his pea plants had different traits – tall or short plants, wrinkled or smooth pods, green or yellow peas, and white or purple flowers.

He conducted an experiment in which he controlled the breeding of the plants through pollination. Through this experiment, he discovered that some traits appeared more often than others.

We now know that those traits are dominant. The other traits that appear less frequently are known as a recessive.

We also know that hybrid offspring result from a combination of a dominant trait and a recessive trait. That said, typically the dominant trait masks or covers the appearance of the recessive trait.

Several years later and a lot more thought into the basics of genetics, Reginald Punnett gave us a graphic representation of what Mendel discovered.

We know this as the Punnett Square. And we can predict the potential offspring of a set of parents using this basic tool.

A Sample Punnett Square

Let’s look at a Punnett Square!

In our sample, we will see the tall/short allele genes - T = tall gene (dominant), t = short gene (recessive). The possible combinations you could get would be:

• dominant tall (TT),
• hybrid tall (Tt),
• and recessive short (tt).

So let's say we create Punnett Square for a dominantly tall (TT) parent and a hybridly tall (Tt) parent. Here is what their possible offspring could look like:

This Punnett square shows us that these parents have:

• a 50% chance of producing a dominant tall offspring,
• a 50% chance of producing a hybrid tall offspring,
• and a 0% chance of producing a recessive short offspring.

And this is how geneticists can use the Punnett square to predict what traits an offspring will have.

Books and Science Activities to Explore the Punnett Square

Want to learn more? Here are a few books and activities to continue the science-fun!

Books to Read

• Gregor Mendel the friar who grew peas
• Gene Machines (Enjoy Your Cells)
• Genetics: Breaking the Code of Your DNA

Punnett Square Science Activities (Including a FREE Printable)

• Lego Punnett Squares - Have the students use a full brick for the dominant trait and a half brick for the recessive trait. Then, have them create several different Punnett Squares using the different options for parents (dominant - 2 full bricks, hybrid - one full brick and one-half brick, and recessive - 2 half bricks).
• Punnett Square Worksheet - Click the link to download a free worksheet to use with your students as you work through this material, including a few sample problems.

I trust that these suggestions will help you teach the Punnett Square to your children! If you have questions along the way, please don't hesitate to share them below.