1. Dihybrid Cross

2. Dihybrid Cross
Not one, but TWO traits

3. Sample Problem
In pea plants, green pods (G) are dominant over yellow pods (g), and smooth pods (N) are dominant over constricted pods (n).
A plant heterozygous for both traits is crossed with a plant that has yellow constricted pods. What are the probable genotypic and phenotypic ratios for this cross?

4. Step 1 Choose letters to represent the genes in the cross.
G = green pods
g = yellow pods
N = smooth pods
n = constricted pods

5. Step 2
Write the genotypes of the parents
GgNn X ggnn

6. Step 3
Determine the possible gametes that the parents can produce (FOIL)
GgNn ggnn gn gn gn gn GN Gn gN gn

7. Step 4
Enter the possible gametes at the top and side of the Punnett square.

8. GgNn X ggnn GN Gn gN gn

9. Step 5
Complete the Punnett square by writing the alleles from the gametes in the appropriate boxes.

10. GgNn X ggnn GN Gn gN gn
GgNn
Ggnn
ggNn
ggnn

11. Step 6
Determine the genotypes and phenotypes of the offspring.

12. Genotypes GgNn 4/16 Ggnn 4/16 ggNn 4/16 ggnn 4/16
Genotypic Ratio - 1:1:1:1

13. Phenotypes Green smooth 4/16 Green constricted 4/16 Yellow smooth 4/16
Yellow constricted 4/16
Phenotypic Ratio - 1:1:1:1

14. Dihybrid Practice problem #1
RrYy (P1) x RrYy (P2)
Problem: Give the genotypic and phenotypic ratios of the offspring.

15. RRYY RrYY RRYy RrYy rrYY rrYy RRyy Rryy rryy RY rY Ry ry RY rY Ry ry
Round yellow
RrYY
RRYy
RrYy
Round Yellow
rrYY
wrinkled yellow
rrYy
Wrinkled Yellow
RRyy
Round green
Rryy
Wrinkled yellow
rryy
Wrinkled green RY rY Ry ry

16. Dihybrid Practice problem #1
--Answer the question
9/16 round yellow
3/16 wrinkled yellow
3/16 round green
1/16 wrinkled green

17. Practice Problem 2
Cross a heterozygous running brown mouse with a heterozygous running, homozygous black mouse. What are the genotypes and phenotypes possible?
Key to alleles:
R=running r=waltzing
B=Black b=brown
Parent 1: Rrbb X Parent 2: RrBB