# Fun with Squares: Punnett Squares and Genetic Probability

Fun with Squares: Punnett Squares and Genetic Probability By Bella Onwumbiko Under the direction of Professor Susan Rodger Duke University July 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/6-8.pdf http://www.ncpublicschools.org/docs/acre/standards/new-standards/science/biology.pdf YOUVE HEARD OF PUNNETT

SQUARES, RIGHT? Scientists use Punnett squares to predict the outcome of breeding experiments! For example, Lets take hamsters! What if one parent has BROWN fur and the other parent has WHITE fur? Lets 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, youll see how simple it can be! 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, youll 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

Do you remember how to fill in a Punnett square? Lets say one parent is heterozygous (brown fur) and the other is also heterozygous (brown fur). B B b b remember how to

A BIT OF DETAIL Dofillyou in a Punnett square? A QUICK REFRESHER b B B B B B b b B b b b Not bad, right? Lets look at the stats: BB, Bb White fur: bb Brown fur: 3 out of 4 (75%) offspring will have brown fur. 1 out of 4 (25%) offspring will have white fur.

Great! Now that you remember how Punnett Squares work, I have some tasks for you to complete. SO HERES THE CHALLENGE: 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 skin texture of the square should change to big B big B The gameScene starts out like this.

When you click on the upperLeftSquare, for example, SO HERES THE CHALLENGE: Here is the order that I want the images to cycle through: blank big B big B little b little b big B little b SO HERES THE CHALLENGE: There are essentially 2 parts to this : Create 4 events:

1) 2) 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.. Dont 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) SOME HELPFUL PICTURE HINTS: 4. 1. 2. 3. 5. THATS 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!

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