Dihybrid Crosses

• Dihybrid cross = a cross where two traits are looked at together
• Each trait is inherited independently (is not affected by the other trait)

How To Do A Dihybrid Cross

1. Write out the genotypes of each parent
2. Number the alleles in each genotype 1-4
3. Draw a 4x4 Punnett square (16 boxes)
4. Write the alleles for the first parent on the top of the large Punnett square
• First box is alleles 1 & 3
• Second box is alleles 1 & 4
• Third box is alleles 2 & 3
• Fourth box is alleles 2 & 4
• You are basically using the FOIL method from math class!!!

5. Write the alleles for the second parent on the side of the large Punnett square
• Same number order you used for step 4
6. Fill in each small square with the offspring genotypes
• Write both alleles for a trait together
• Example: AaBB is correct, ABaB is wrong

Example Dihybrid Cross

• In pea plants, tall (T) is dominant to short (t), and axial flowers (A) are dominant to terminal flowers (a). Cross a pea plant that is homozygous for tall height and heterozygous for axial flowers with a plant that is heterozygous for both traits.

Example Dihybrid Cross

• Write out the genotypes of each parent plant
• TTAa x TtAa
• Fill-in the parents on a 4x4 Punnett square
• Fill-in the offspring on the 4x4 Punnett square