Dihybrid crossDihybrid cross

Complete dominanceComplete dominance

Example: Coat color and Example: Coat color and Polled/horned condition in Polled/horned condition in

cattlecattle

Black coat (B) is Black coat (B) is dominant over red dominant over red coat (b)coat (b)

Polled (no horns) Polled (no horns) condition (P) is condition (P) is dominant over dominant over horned condition horned condition (p)(p)

Cross two individuals who Cross two individuals who are heterozygous for both are heterozygous for both

traits:traits:

BbPp X BbPpBbPp X BbPp

Both individuals have Both individuals have

black coats and are polledblack coats and are polled

Alleles BP Bp bP bp

BP

Bp

bP

bp

BbPp X BbPp

BP Bp bP bp

BP BBPP BBPp BbPP BbPp

Bp BBPp BBpp BbPp Bbpp

bP BbPP BbPp bbPP bbPp

bp BbPp Bbpp bbPp bbpp

BbPp X BbPp

Genotypic outcomesGenotypic outcomes 1 BBPP1 BBPP 2 BbPP2 BbPP 1 bbPP1 bbPP 2 BBPp2 BBPp 3 BbPp3 BbPp 2 bbPp2 bbPp 1 BBpp1 BBpp 2 Bbpp2 Bbpp 1 bbpp1 bbpp

16 combinations16 combinations 9 possible 9 possible

outcomesoutcomes Genotypic ratioGenotypic ratio

1:2:1:2:3:2:1:2:11:2:1:2:3:2:1:2:1

Phenotypic outcomesPhenotypic outcomes

9 Black coat, Polled9 Black coat, Polled

1 BBPP 1 BBPP

2 BBPp 2 BBPp

2 BbPP2 BbPP

4 BbPp 4 BbPp

(All of the genotypes above produce (All of the genotypes above produce the same phenotype)the same phenotype)

Phenotypic outcomesPhenotypic outcomes

3 Black coat, horned3 Black coat, horned

1 BBpp, 2 Bbpp1 BBpp, 2 Bbpp 3 Red coat, Polled3 Red coat, Polled

1 bbPP, 2 bbPp1 bbPP, 2 bbPp 1 Red coat, horned1 Red coat, horned

1 bbpp1 bbpp

Phenotypic outcomesPhenotypic outcomes

Phenotypic ratioPhenotypic ratio

9:3:3:19:3:3:1