Question

The phenotype ratio of a dihybrid cross in which both the genes show incomplete dominance is

• A. 1 : 2 : 1
• B. 9 : 3 : 3 : 1
• C. 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1
• D. 3 : 1

Answer 1

The correct option is C 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1

• Incomplete dominance is the condition where a dominant trait fails to show dominance completely in the heterozygous condition. For example, in snapdragon homozygous dominant results in the red color of the flower while homozygous recessive results in white flower. While heterozygous condition results in the pink color of the flower.
• Hence, in each case of incomplete domination, the heterozygous condition will result in a new phenotype.
• Following Punnet's square is representing dihybrid cross for genes A and B showing incomplete domination -

  	AB	Ab	aB	ab
  AB	AABB	AABb	AaBB	AaBb
  Ab	AABb	AAbb	AaBb	Aabb
  aB	AaBB	AaBb	aaBB	aaBb
  ab	AaBb	Aabb	aaBb	aabb
• As we can see by counting phenotype ratio is same as genotype ratio here i.e. 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1.
• So, the correct option is '1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1'.