Question

What percentage of progenies would have broad leaves and pink flowers in F2 generation of the Snapdragon if the first trait follows the law of dominance and the other shows incomplete dominance?
A. 37.5%
B. 56.25%
C. 62.5%
D. 12.5%

Answer 1

In heterozygous condition, when the dominant gene is not completely dominant over the recessive gene and can’t express themselves completely they show an intermediate phenotype. This phenomenon is known as incomplete dominance. Incomplete dominance is also known as partial dominance or intermediate inheritance.

Complete answer:
Let us assume that gene B is responsible for the width of the leaf. Where, BB is responsible for broad leaves and bb is responsible for narrow leaves.
Snapdragon shows incomplete dominance in flower color. In snapdragon RR is responsible for red color flowers, rr is responsible for white color and Rr gene shows pink color.
Dihybrid cross for F2 generation in Snapdragon can be shown as below -

Gamete type	BR	Br	bR	br
BR	BBRR	BBRr	BbRR	BbRr
Br	BBRr	BBrr	BbRr	Bbrr
bR	BbRR	BbRr	bbRR	bbRr
br	BbRr	Bbrr	bbRr	bbrr

BbRr- Broad leaves and pink color - 4
BBRr- Broad leaves and pink colour- 2
As we see in this chart, 6 out of 16 (Genotypes BbRr and BBRr) progenies will have broad leaves and pink flowers which is equal to 37.5%.

So, the correct answer is option A. '37.5%'.

Note:
Incomplete dominance is a type of allelic gene interaction. In incomplete dominance the phenotypic characters shown by the progeny in F1 generation will be intermediate.
The intermediate characters don’t resemble any of the parents' characters.
Incomplete dominance examples are shown in Flower color of four o’clock flowers (Mirabilis jalapa), Flower color of snapdragon, Feather color of andalusian fowl, etc.