Dihybrid Cross

Estimated time: 12 minutes

CBSE: Class 12
Maharashtra State Board: Class 12
CISCE: Class 12

Definition: Dihybrid Cross

Mendel investigated not only those crosses in which the parent differed in single pair of characters, but also others in which the parent differed in two pairs. Such a cross which involves two pairs of contrasting characters simultaneously is called dihybrid cross.
A genetic cross involving two pairs of contrasting characters simultaneously is called a dihybrid cross.

CBSE: Class 12
Maharashtra State Board: Class 12
CISCE: Class 12

Traits Studied

Character	Dominant Form	Recessive Form	Symbol Used
Seed Shape	Round	Wrinkled	R (Round), r (wrinkled)
Seed Colour	Yellow	Green	Y (Yellow), y (green)

Parental Generation (P Generation)

F₂ Phenotypes: Sorting the 16 Offspring

Phenotype	Genotypes Included	Count	Fraction
Round Yellow (both dominant)	RRYY, RRYy, RrYY, RrYy	9	9/16
Round Green (R dominant, Y recessive)	RRyy, Rryy	3	3/16
Wrinkled Yellow (R recessive, Y dominant)	rrYY, rrYy	3	3/16
Wrinkled Green (both recessive)	rryy	1	1/16

F₂ Phenotypic Ratio = 9 : 3 : 3 : 1

Understanding the Genotypic Ratio: 1:2:2:4:1:2:1:2:1

Genotype	Count	Notes
RRYY	1	Pure dominant for both
RRYy	2	Pure Round, heterozygous Yellow
RrYY	2	Heterozygous Round, pure Yellow
RrYy	4	Heterozygous for BOTH — most frequent class
RRyy	1	Pure Round, pure Green
Rryy	2	Heterozygous Round, pure Green
rrYY	1	Pure Wrinkled, pure Yellow
rrYy	2	Pure Wrinkled, heterozygous Yellow
rryy	1	Pure recessive for both (parental type)

CBSE: Class 12
Maharashtra State Board: Class 12

Parameter	Dihybrid Cross
Meaning	Cross involving 2 pairs of contrasting characters
Example	TTRR × ttrr (Tall Round × Dwarf Wrinkled)
Phenotypic Ratio	9 : 3 : 3 : 1 (Tall Round : Tall Wrinkled : Dwarf Round : Dwarf Wrinkled)
Genotypic Ratio	1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1
Conclusion	Tall/dwarf and round/wrinkled traits are independently inherited