1. Dihybrid Cross Notes
Have your
Monohybrid
Notes
Out!

2. Example
Heterozygous, black, hairless male mouse is crossed with a white heterozygous hairy female mouse.

3. 1. Determine dominant and recessive traits Will be stated in
Heterozygous, black, hairless male mouse is crossed with a white heterozygous hairy female mouse.
Step
Notes
Example
1. Determine dominant and recessive traits
Will be stated in
the problem
Black is dominant to white
Hairy is dominant to hairless

4. 2. Assign letters for the trait Dominant trait gets the capital letter
Heterozygous, black, hairless male mouse is crossed with a white heterozygous hairy female mouse.
Step
Notes
Example
2. Assign letters for the trait
Dominant trait gets the capital letter
Recessive traits gets the lower case letter
B = black
b = white
H = Hairy
h = hairless

5. 3. Determine genotype for parents Each parent must have 4 alleles
Heterozygous, black, hairless male mouse is crossed with a white heterozygous hairy female mouse.
Step
Notes
Example
3. Determine genotype for parents
Each parent must have 4 alleles
Each parent will have has two alleles for two traits
Heterozygous, black, hairless male = Bbhh
White heterozygous hairy female = bbHh

6. There will be 16 boxes total
Heterozygous, black, hairless male mouse is crossed with a white heterozygous hairy female mouse.
Step
Notes
Example
4a. Draw a 4x4 square
There will be 16 boxes total

7. 4b. Put parent gamete combinations on box Separate parental alleles
Heterozygous, black, hairless male mouse is crossed with a white heterozygous hairy female mouse.
Step
Notes
Example
4b. Put parent gamete combinations on box
Separate parental alleles
Think of it like distributing
You should have four possible combination
Bbhh gametes:
Bh, Bh, bh, bh
bbHh gametes:
bH, bh, bH, bh

8. Step 4b.
Bh Bh bh bh bH bh

9. 5. Determine genotype of offspring
Heterozygous, black, hairless male mouse is crossed with a white heterozygous hairy female mouse.
Step
Notes
Example
5. Determine genotype of offspring
Punnett square holds offspring genotypes
Genotype = letter code
You should have
16 possible offspring

10. Step 5.
Bh Bh bh bh bH bh
BbHh
bbHh
Bbhh
bbhh

11. 5. Determine genotype of offspring
Heterozygous, black, hairless male mouse is crossed with a white heterozygous hairy female mouse.
Step
Notes
Example
5. Determine genotype of offspring
Punnett square holds offspring genotypes
Genotype = letter code
You should have
16 possible offspring

12. 6. Determine genotype ratio Count offspring in the Punnett square
Heterozygous, black, hairless male mouse is crossed with a white heterozygous hairy female mouse.
Step
Notes
Example
6. Determine genotype ratio
Count offspring in the Punnett square
You should have
16 possible offspring
4 BbHh
4 Bbhh
4 bbHh
4 bbhh

13. 7. Determine phenotype ratio Phenotype = what they look like
Heterozygous, black, hairless male mouse is crossed with a white heterozygous hairy female mouse.
Step
Notes
Example
7. Determine phenotype ratio
Phenotype = what they look like
You have two traits to describe!
*ratio MUST add up to the number of boxes*
4 Black Hairy
4 Black Hairless
4 White Hairy
4 White Hairless

14. Genotype Practice
1. In bunnies, black is dominant to white. Rough is dominant to smooth.
Give the genotype for each of the following:
a. Homozygous black, smooth bunny: _____________
b. Heterozygous black-rough bunny: _____________
c. White, homozygous rough bunny: _____________
d. White, smooth bunny: _____________
e. Homozygous black-rough bunny: _____________
f. White, heterozygous rough bunny: _____________

15. Gamete Combination Practice
2. Give the gamete combination for each genotype.
a. AATt _____, _____, _____, _____
b. AaTT _____, _____, _____, _____
c. aatt _____, _____, _____, _____
d. AAtt _____, _____, _____, _____

16. 3. In hamsters, black coat is dominant to white coat and rough coat is dominant to smooth coat. Two heterozygous black-rough coated hamsters where mated.
a. Give the genotype cross: ____________x____________
b. List the possible gametes formed by each parent.
____, ____, _____, _____

17. 3. In hamsters, black coat is dominant to white coat and rough coat is dominant to smooth coat. Two heterozygous black-rough coated hamsters where mated.
d. What would be the genotype ratio of the F1 generation?
___ BBRR : ___ BBRr : ___ BBrr : ___ BbRR :
___ BbRr : ___ Bbrr :
___ bbRR : ___ bbRr :
___ bbrr
e. What would be the phenotype
ratio of the F1 generation?
____ Black-Rough :
____ Black-Smooth :
____ White-Rough :
____ White-Smooth