Inheritance of Two Traits: Dihybrid Crosses

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 seti * * 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. Phenotypic ratio (Dom/Dom) Round/Yellow: (Dom/Rec) Round/green: (Rec/Dom) wrinkled/Yellow: (Rec/Rec) wrinkled/green: Dihybrid Cross F RY O Ry I rY L ry RY Ry rY ry

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

9. Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio Dihybrid Cross