Fun with Squares: Punnett Squares and Genetic Probability

By Bella OnwumbikoUnder the direction of Professor Susan Rodger

Duke UniversityJuly 2013

MAPPING TO NORTH CAROLINA BIOLOGY STANDARDS…In 7th grade, students should be able to use Punnett squares to infer patterns of heredity:

Students should also be able to predict offspring ratios (easily done using Punnett squares):

http://www.ncpublicschools.org/docs/acre/standards/new-standards/science/biology.pdf

http://www.ncpublicschools.org/docs/acre/standards/new-standards/science/6-8.pdf

YOU’VE HEARD OF PUNNETT SQUARES, RIGHT?

Scientists use Punnett squares to predict the outcome of breeding experiments!

Let’s take hamsters! What if one parent has BROWN fur and the other parent has WHITE fur? Let’s assume there is a complete dominance such that the BROWN fur color is dominant and WHITE is recessive.

What is the probability that the child of these two parents will have WHITE fur?

The question sounds tough at first, but once we take a closer look, you’ll see how simple it can be!

For example,

A BIT OF DETAIL… A QUICK REFRESHER…

Go and play the punnettSquares_Challenge.a2w Alice World. Keep watching until Dr. Gene asks you to fill in the Punnett square. Later on, you’ll have to write some code for that part to work!The beginning gives a quick review of inheritance terms like:

• Allele,• Dominant,• Recessive,• Homozygous, and• Heterozygous

Let’s say one parent is heterozygous (brown fur) and

the other is also heterozygous (brown fur).

Do you remember how to fill in a Punnett square?

B

b

Bb

A BIT OF DETAIL…A QUICK REFRESHER…

Not bad, right? Let’s look at the stats:

Do you remember how to fill in a Punnett square?

B

b

BB BBbb

b bbBBrown fur:

White fur:

BB, Bbbb

3 out of 4 (75%) offspring will have brown fur.

1 out of 4 (25%) offspring will have white fur.

SO HERE’S THE CHALLENGE:

Great! Now that you remember how Punnett Squares work, I have some tasks for you to complete.

Fill in the code in punnetSquares.a2w to make it such that when you click on one of the four squares that make up the Punnett squares, it will cycle through the different answer choices: a blank square, BB, Bb, and bb.

Picture this!The gameScene starts

out like this.

When you click on the upperLeftSquare, for

example,

the skin texture of the square should change

to big B big B

SO HERE’S THE CHALLENGE:Here is the order that I want the images to cycle through:

“blank” “big B big B”

“big B little b”“little b little b”

SO HERE’S THE CHALLENGE:There are essentially 2 parts to this :

Create 4 events: • When you click on the square (upperLeftSquare,

lowerLeftSquare, upperRightSquare, lowerRightSquare), you want to cycle through the images that I described on the last slide.

Complete the cycleThroughImages method:• I set up the if/else structure that you will need. • Example- If the skin texture of the square is blank, change the

skin texture to big B big B. Else, if the skin texture of the square is big B big B, change the skin texture to big B little b. Else, if…..

• Don’t really get it? If you are having some trouble with this logic sequence, I suggest you try doing the Changing Color: Advanced Function tutorial on the Duke Alice Programming website (each time you click on a chicken, you change its color, in a cycle)

1)

2)

SOME HELPFUL PICTURE HINTS:

1.

2.

3.

4.

5.

THAT’S IT!

Once you think you have gotten all of your events set up, and you think the cycleThroughImages method is functional, PLAY THE WORLD!

When Dr. Gene asks you to fill out the Punnett square, try clicking on each of the four squares. If you did it successfully, the order in which the images cycle will be:

“blank” “big B big B” “big B little b” ”little b little b”

You should be able to play through the rest of the world once you finish solving this challenge!

Good Luck!