Question

The $F_2$ phenotypic ratio of 1 : 2 : 1 is obtained in those crosses that exhibit

• A. Complete dominanc
• B. Partial dominance
• C. Co-dominance
• D. Both B and C

Answer 1

The correct option is D Both B and C

Partial dominance	R	r
R	RR (red)	Rr (pink)
r	Rr (pink)	rr (white)

Co-dominance	A	B
A	AA (A blood group)	AB (AB blood group)
B	AB (AB blood group)	BB (B blood group)

Partial dominance is also known as incomplete dominance. It occurs when the dominant allele is not able to mask the effect of the recessive allele completely. It is commonly seen in Snapdragon and Mirabilis jalapa. In F${}_2$ generation, the red allele cannot completely mask the effect of white allele resulting in a new phenotype i.e. pink.

Co-dominance occurs when both the alleles show their effects equally. In AB blood group system, A allele and B allele both express equally resulting in new blood group i.e. AB blood group.

The phenotypic ratio in both F${}_2$ generation is 1: 2: 1 i.e. red: pink: white or A: AB: B blood group.

So, the correct option is 'Both B and C'.