1. Dihybrid crosses

2. In Monohybrid crosses we predicted the probability of inheriting one trait. If the probability of inheriting one trait can be predicted, can the probability of inheriting two or more traits also be predicted?

3. *Dihybrid Cross*
Probability of inheriting 2 traits can be predicted by a Dihybrid cross
Di = 2 traits
Hybrid = cross between different parents

4. *Dihybrid Cross*
The dihybrid cross is a 4 column x 4 row table, representing16 possible genetic combinations total.
Each parent’s gametes can result in 4 possible allele combinations (hence the 4 x4 cross).
Refer to “How to Set Up a Punnett Square”

5. Setting up the dihybrid cross
Determine the parent genotypes
Determine the possible gametes that can form when alleles segregate. Use the FOIL method (click here next slide).
Place each gamete combination (2 different letters; e.g AB, aB, or ab) for one parent over each column of the cross
Do the same for the other parent to the left of each row of the 4 x 4 cross
Follow the arrow…

6. *F.O.I.L method* A a B b First (AB) Outer (Ab) Inner (aB) Last (ab)
Sample genotype for 2 traits:
A a B b
(Note: parent is heterozygous for both traits)
Possible gamete combinations:
First (AB)
Outer (Ab)
Inner (aB)
Last (ab)
Follow the arrow…

7. Setting up the dihybrid cross
What are the parent genotypes?
What possible gametes can form from the parents genotypes when alleles segregate?
You try!!
AaBB=
AaBb=
aaBb=
Aabb=

8. Parents (p1) Genotypes: AaBb x AaBb

9. Offspring (F1) Genotype Outcomes

10. Interpreting the results….
To provide the Phenotypic ratios you just count the boxes that are displaying the similar results.

11. Try this dihybrid cross…
Tall tomato plants are produced by the action of a dominant allele T and dwarf plants by its recessive allele t. Hairy stems are produced by a dominant gene H and hairless stems by its recessive allele h. A heterozygous tall, hairy plant is crossed with a dwarf hairless tomato plant.
Determine the phenotypic ratio for the F1 generation. Show cross and give ratio.