Genetics: Penny Flip

Use this activity to make the Punnett Square percentages come to life.

For this example, I'm using two heterozygous parents: Rr x Rr. 

Each student/pair of students will need two pennies - one for each parent. 

Use a small piece of masking tape to write the genotype on the pennies - one letter of the genotype goes on each side of the penny.

Then start flipping your pennies and tallying the results.  One student could flip both pennies, or if working in pairs, have each student flip one. 

They should be able to get a lot of flips in very quickly and amass a good set of data.  It's amazing how close they'll come to the 25% - 50% - 25% results.  It's even more striking when you combine the whole class data. 

I actually did it and that's how it worked out - I didn't make up the data! 

For students who are still struggling, have them use the pennies to do other crosses:
RR x rr
RR x RR
rr x rr
and so on

I find that this activity helps students begin to understand what offspring are possible from given parents.  It also helps drive home the point that each parent contributes one gene to the offspring.


You could just have them use heads and tails, but marking the genotypes makes it much clearer (especially for struggling students, for whom this activity is the most beneficial).