1. Inheritance of Two Traits: Dihybrid Crosses
Learning goal:
Predict the inheritance patterns and combinations of alleles in gametes of individuals heterozygous for two traits.

2. Determine the inheritance of two traits
Two traits in pea plants are seed shape and seed color.
R is the allele for the dominant, round shape characteristic;
r is the allele for the recessive, wrinkled shape characteristic.
Y is the allele for the dominant, yellow color characteristic;
y is the allele for the recessive, green color characteristic.

3. Distribution of alleles in gametes
Assortment of Rr alleles
The gametes from the RrYy parent will receive one of the two alleles Rr.
Half will receive the dominant R allele, and half the recessive r allele.

4. Distribution of alleles in gametes
Assortment of Yy alleles
The gametes from the RrYy parent will also receive one of the two alleles Yy.
Half will receive the dominant Y allele, and half the recessive y allele.

5. FOIL to determine gametes
A quick way to determine the possible gametes (R r) (Y y)
F.irst of each set i * * RY
O.uter allele of each * * Ry
I.nner allele of each * * rY
L.ast allele of each * * ry
These combinations of alleles will go in the rows or columns of your dihybrid Punnett square

6. Draw your Dihybrid Punnett Square
1. Draw a rectangular box
2. Cut the box in half
3. Cut each half in half
4. Cut in half the other way  
5. Cut each of those in half
Now you’re ready to set up the cross RrYy x RrYy

7. Dihybrid Cross F RY O Ry I rY L ry Round/Yellow: Round/green:
Mendelian Genetics
4/24/2017
Dihybrid Cross F RY O Ry I rY L ry
(Dom/Dom)
Round/Yellow:
(Dom/Rec)
Round/green:
(Rec/Dom)
wrinkled/Yellow:
(Rec/Rec)
wrinkled/green:
Phenotypic ratio RY Ry rY ry

8. Dihybrid Cross RY Ry rY ry Round/Yellow: 9 Round/green: 3
Mendelian Genetics
4/24/2017
Dihybrid Cross RY Ry rY ry
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1 phenotypic ratio
RRY
RRYy
RrYY
RrYy
RRyy
Rryy
rrYY
rrYy
rryy

9. Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3
Mendelian Genetics
4/24/2017
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1 phenotypic ratio