1. DIHYBRID PUNNETT SQUARES

2. Dihybrid Cross: a cross that shows the possible offspring for two traits
Trait one
Trait Two
Coat Texture: R: Rough r: Smooth
Fur Color: B: Black b: White
Step 1: FIND OUT THE GENOTYPES OF THE PARENTS In this example, we will cross a heterozygous individual with another heterozygous individual. Their genotypes will be:
BbRr x BbRr

3. Dihybrid Cross BbRr x BbRr
Step 2:FOIL EACH PARENT TO SHOW THE POSSIBLE GAMETE COMBINATIONS Remember, each gamete must have one B and one R.
DAD
MOM

5. F.O.I.L.
PARENT 1
PARENT 2
BbRr
BbRr Br br BR bR Br br BR bR

6. Practice What are the possible gametes for BBrr
What are the possible gametes for HhTT?

7. BbRr x BbRr Dihybrid Cross DAD MOM
Step 3:SET UP PUNNETT SQUARE: Arrange all possible gametes for dad on the top of your Punnett Square, and mom down the side

8. Dihybrid Crosses: a cross that shows the possible offspring for two traits
BbRr x BbRr BR bR br Br
Fur Color: B: Black b: White B B R R B B r R b B R R b B r R
Coat Texture: R: Rough r: Smooth B B r r b B R r B B R r b B r r
Step 4: Fill in the Punnett Square (find the possible genotypes of the offspring) B b R B b r R b b R R R b b r R B b R r B b r r b b R r b b r r

9. How many of the offspring would have a black, rough coat?
How many of the offspring would have a black, smooth coat?
How many of the offspring would have a white, rough coat?
How many of the offspring would have a white, smooth coat? BR bR br Br
BBRR
BbRR
BbRr
BBRr
BBrr
Bbrr
bbRR
bbRr
bbrr
Fur Color: B: Black b: White
Coat Texture: R: Rough r: Smooth

10. How many of the offspring would have black, rough coat?
How many of the offspring would have a black, smooth coat?
How many of the offspring would have a white, rough coat?
How many of the offspring would have a white, smooth coat? BR bR br Br
BBRR
BbRR
BbRr
BBRr
BBrr
Bbrr
bbRR
bbRr
bbrr
Phenotypic Ratio=
9:3:3:1
Fur Color: B: Black b: White
Coat Texture: R: Rough r: Smooth

11. Practice in your notes…
In pea plants, yellow seeds (Y) are dominant over green seeds (y), and rounded peas (R) are dominant over wrinkled peas (r). Cross a plant that is heterozygous for both traits with a plant that is homozygous recessive for both traits. Draw a Punnett square to show all possible offspring, and determine the genotypic and phenotypic ratios.

12. YyRr X yyrr YR yR yr Yr
YyRr
yyRr
yyrr
Yyrr

13. More Practice
Work on the SpongeBob Dihybrid Cross worksheet. Turn it in at the end of class.