How do you do probabilities with punnett squares?

1 Answer
Nov 9, 2016


The number of squares with the outcome divided by the total number of squares. This can be expressed as a fraction or percentage.


A Classic example is the bi hybrid cross of both parents being brown /blonde

 Mother          B         b      Father

B | B B | B b |
b | b B | b b |

There is one off spring square bb that will give rise to a blonde
off spring There are four total squares.

So the probability is 1/4 of having a blonde child This translates to a 25% probability of having a blonde.

There are three square that will result in a brown haired offspring.

so the probability of a a brown haired off spring is 3 out of 4 or

3/4 or 75 %