1. Example: Let’s examine a dog’s hair color AND a dog’s eye color
Dihybrid Cross
A cross between individuals which examines and predicts TWO trait combinations at one time
Example: Let’s examine a dog’s hair color AND a dog’s eye color
Brown hair (B) is dominant to white hair (b)
Green eyes (G) are dominant to blue eyes (g)

2. Remember… Law of Segregation: Law of Independent Assortment:
Alleles for the same gene separate during meiosis.
B’s will separate from B’s
G’s will separate from G’s
Law of Independent Assortment:
Allele pairs (traits) separate independently of other allele pairs (traits).
Hair color and eye color in dogs do not depend on one another

3. Mommy Dog
Let’s say our mom dog is heterozygous for her brown fur and heterozygous for green eyes.
What is her genotype?
BbGg
She can produce eggs with what combinations? Remember, the B alleles and G alleles will get split during meiosis!

4. BbGg
FOIL! BG Bg bG bg

5. Daddy dog
What if the dad is homozygous for brown hair and has blue eyes?
Genotype?
BBgg
Allele combinations?

6. BBgg
FOIL! Bg Bg Bg Bg

7. Now let’s set up our cross!BG Bg bG bg Bg Bg Bg Bg

8. Now let’s set up our cross!BG Bg bG bg
BBGg
BBgg
BbGg
Bbgg Bg Bg Bg Bg

9. By the Numbers How many offspring have: Brown fur and green eyes?
8, 50%
Brown fur and blue eyes?
White fur and green eyes?
0, 0%
White fur and blue eyes?

10. What about this cross? BbGg x BbGg

11. What about this cross? BbGg x BbGg

12. What about this cross? BbGg x BbGg

13. By the Numbers How many offspring have: Brown fur and green eyes?9
Brown fur and blue eyes? 3
White fur and green eyes?
White fur and blue eyes? 1

14. Now try one on your own…
Mommy dog has white fur and is heterozygous for green eyes.
Daddy dog is heterozygous for his brown fur and has blue eyes.
How many dogs would you expect to have brown hair and green eyes?
Brown hair and blue eyes?
White hair and green eyes?
White hair and blue eyes?

15. bbGg x Bbgg

16. bbGg x Bbgg bG bg bG bg Bg Bg bg bg

17. bbGg x Bbgg bG bg bG bg
BbGg
Bbgg
bbGg
bbgg Bg Bg bg bg

18. By the Numbers How many offspring have: Brown fur and green eyes?4
Brown fur and blue eyes?
White fur and green eyes?
White fur and blue eyes?