1. 3-3B. Punnett Squares (Part 2: Dihybrid crosses)

2. A dihybrid cross involves two traits.
The Di-hybrid cross uses a punnett square with 16 boxes

3. First, let’s read the genotypes
In Cows, Black is dominant to red AND Fat is dominant to skinny
A = Black B = Fat
a = Red b = Skinny
AAbb
aaBb
Black, Skinny
Red, Fat
AaBB
AaBb
Black, Fat
Black, Fat

4. Now, let’s write the genotypes
A = Black B = Fat
a = Red b = Skinny
A heterozygous black cow that is skinny
Aabb
A red skinny cow
aabb
A cow that is homozygous dominant for both traits
AABB
A cow that is homozygous black and heterozygous fat.
AABb

5. Now, let’s throw cow shoes……
A = Black B = Fat
a = Red b = Skinny
A homozygous black, skinny cow is bred to cow that is heterozygous for both traits
What is mom?
AAbb
What is dad?
AaBb
Aabb x AaBb

6. Filling out the punnett square
A = Black B = Fat
a = Red b = Skinny
Aabb x AaBb
Move to the board……