How to do a genetic cross to work out the offspring phenotype probabilites?

Construct a punnet square, putting the gametes of one parent in the first vertical column and the other parent in the first horizontal column. Next carry out the cross by combining the gametes in the squares. This will give you the expected probability of offspring phenotypes. You can use this method to work out the probability of a child having a certain characteristic or genetic condition, depending on whether it is dominant or recessive.