Question

Explain a dihybrid cross with suitable example and checker board method.

Answer 1

The phenotypic ratio of different types of offsprings (with different combinations) obtained in F₂ generation of dihybrid cross is called the dihybrid ratio. It is 9 : 3 : 3 : 1.

For example, when we cross a yellow round seed pea plant with a green wrinkled seed pea plant, we get 9 yellow round, 3 yellow wrinkled, 3 green round and 1 green wrinkled plants in the F₂ generation.

F₂ generation → 

→	YR	Yr	yR	yr
↓
YR	YYRR Yellow round	YYRr Yellow round	YyRR Yellow round	YyRr Yellow round
Yr	YYRr Yellow round	YYrr Yellow wrinkled	YyRr Yellow round	Yyrr Yellow wrinkled
yR	YyRR Yellow round	YyRr Yellow round	yyRR Green round	yyRr Green round
yr	YyRr Yellow round	Yyrr Yellow wrinkled	yyRr Green round	yyrr Green wrinkled

Phenotypic ratio: Yellow round = 9 ;Yellow wrinkled = 3; Green round = 3; Green wrinkled = 1

Dihybrid ratio → 9 : 3 : 3 : 1

Genotypic ratio →  YYRR : YYRr : YyRR : YyRr : YYrr  : Yyrr : yyRR : yyRr : yyrr

  Genotypic ratio → 1  :   2   :   2  :  4  :   1  :  2  :   1   :  2  :   1