1. Dihybrid Crosses
Because some traits affect each other or are related, we can also show the inheritance of 2 traits together.
Considering 2 traits together involves a dihybrid cross.
Looking at a cross, in pea plants, that considers the traits round seed, dominant to wrinkle seeds, and Yellow peas, dominant to green peas.
Our cross would be RrYy x RrYy for 2 double heterozygous plants…. The Punnett square would look like this….

2. Let’s Look at a dihybrid cross between 2 heterozygous yellow round seed pea plants. (Yellow and Round are dominant traits.

3. How do you set this up?
First, draw a box, then divide the box down the middle vertically and across the middle horizontally.
Now divide the left and right side with a vertical line and divide the top and bottom with a horizontal line.
RrYy x RrYy
Now you have 16 inner squares.
Take the 1st letter of the 1st trait and the 1st letter of the second trait….then the 1st with the 2nd letter of the second trait…then the second letter of the 1st trait with the 1st letter of the second trait and finally the 2nd letter of the 1st trait with the second letter of the 2nd trait.
This gives you 4 trait pairs…put them in the 4 slots at the top…do the same for the other parent on the side.

5. Now You Try One
Tall is dominant to short, in pea plants, and round seeds are dominant to wrinkled seeds.
Show a cross of 2 double heterozygous plants.
Also show the x format for the cross.
Remember…if you have one trait, you will have a 4 square. If you have 2 traits, you will have a 4x4 16 square.

6. Here is your answer…great job if you got it without looking, these are tough! TtRr x TtRr