Dihybrid Crosses: Crosses that involve 2 traits.

For these crosses your punnet square needs to be 4x4

In any case where the parents are heterozygous for both traits (AaBb x AaBb) you will get a 9:3:3:1 ratio.

If you cross other combinations, you will need to do a square. Try RrYy x rryy. Click to see solution.