Imaginary Friend Builder

Biology:	Punnet Squares
Grade Range:	Middle School, High School
Format:	Hands-on, Stage

This is a creative and silly way to introduce Punnet Squares to students. This demonstration is intended to be led by the students, so don't be surprised if you get some extra silly results!

Materials

Hands-on

• List of Traits
• Punnet Square Printouts
• Coins
• Pencils
• Coloring Supplies (Crayons, markers, etc.)

Stage

• List of Traits
• White Board
• Imaginary Friend Cutout
• Cutouts of Additional Traits
• Giant Die or Coin

Safety Precautions

Please read the General Safety Precautions section of the Demonstration Safety page before performing this demonstration.

Demonstration

Hands-on

1. Give each student a printout and a pencil. Have them look at the list of traits and choose the top option they like for each pair. Once they have gone through all the options, Have them draw their imaginary friend on the back of the printout.

2. Have students pair up, and compare their chosen lists of traits. Have them make a third list of traits, Where they write each of their chosen traits next to each other, even if they match.

3. Give each student pair a coin, and have them use the squares to decide what traits will be used in their combined imaginary friend.

• For their list of traits, they should label the traits on the left as "A" and the traits on the right as "B". In their square they should label the four coordinates as:

AA	AB
BA	BB

4. For each of their trait pairs, the groups will flip the coin to decide which one is dominant. Heads means A, tails means B. They will flip the coin twice for each trait pair, and record the coin flip results in order. That way, if they get a heads and tails, they know that it is AB, while a tails and heads would be BA.

5. Once they get their coin flip results for each trait pair, they can try to draw their new, third imaginary friend. The letter in front is the dominant letter, so it will be the shown trait. The second letter is the recessive letter, so it isn't necessarily shown, but they can choose to have it affect the result.

• For example, a AB set for (Tail)/(No Tail) could mean that it has a short tail, while an AA set could mean that it has a long tail.
• Another example is that a BA set for (Purple skin)/(Green skin) could mean that it has green skin with purple spots or stripes.

Stage

1. Explain to the audience that you want an imaginary friend, but need help in making them. Draw out the Punnet Square on the whiteboard and explain that you will be using it to build the imaginary friend.
2. Show the imaginary friend cutout and ask the audience which color it should be: Green or Purple? Determine the more popular vote and label it as A, and label the less popular one as a. Label the coordinates of the punnet square and use the coin/die to determine what trait is shown.
3. Go through the other possible traits with the same method. Build the imaginary friend as you go, adding the traits onto the figure as they are determined.
4. Once you finish building your imaginary friend, thank the audience for their help in creating it! Be sure to explain that this passage of traits is what led to everyone on earth being unique!

Why This Works

Punnett Squares are a tool used by biologists to predict what traits will be passed on. When looking at a possible breeding experiment, one would want to try and predict the Genotype, or the genetic makeup of the offspring. If this can be predicted, than one can make an educated guess at the Phenotype, or the traits that are expressed by the genes in the organisms.

Traits in an organism are either primary or recessive. Primary traits are those genes which are more likely to be expressed. Recessive traits are those genes which are less likely to be expressed. In other words, primary traits are common and recessive traits are uncommon. When looking at the genotype and phenotype of an organism, the likelihood of certain common or uncommon traits can be predicted based on the genes passed on.

We can use the example below to see how traits are predicted:

Punnet Square Example

Eye Color:	Green (G)	Blue (b)
Blue (B)	GB	Bb
Blue (b)	Gb	bb

In this example, we have two expressed traits (Blue and Green) and two recessive traits (blue and blue). If we follow the steps from the demonstration, we would flip a coin to see which of the first parent's traits (Green and blue) would be passed on, with a 50% chance for Green. The second coin flip would be for the second parent's traits (Blue and blue), which are guaranteed blue. Blue is guaranteed to be expressed in at least two of the cases, whereas Green is only guaranteed in one case. This allows us to predict the offspring to be more likely to have blue eyes, with a 67% higher chance than green.

If GB is selected, than either primary trait can be used, with both being primary traits for that organism's offspring. If bb is selected, than blue is the trait used, but both traits will be recessive in that organism's offspring. This shows us not only how traits are passed from generation to generation, but how unique the traits are as they go from one generation to the next!

Additional Information

• This demonstration works well in the classroom as a lesson on Punnett Squares. It also works well for science nights, and gives students the chance to see what traits were passed to them or their siblings from their parents.
• This demonstration pairs well with the Predator Prey demonstration.