Summary OCR A-Level Biology 6.2.3 Dihybrid Inheritance

Dihybrid Inheritance
Monohybrid Cross
 Dihybrid = determined by two gene loci
 Results in a 9:3:3:1 ratio
 Example: Dominant = T Recessive = t
 Homozygous Dominant = TT Heterozygous = Tt Homozygous Recessive = tt
 Punnett Squares:


Parent Phenotype Double Heterozygous x Double Heterozygous
Parent Genotype AaBb x AaBb
Parent Gametes AB Ab aB ab AB Ab aB ab
Dihybrid Cross AB Ab aB ab
A AAB AAB
AABB
B b AaBb b
A AAb
AABb
b b AaBb Aabb
AAB
aB AaBb b aaBB aaBb
ab AaBb Aabb aaBb aabb

Ratio AB = 9
Ab = 3
aB = 3
ab = 1