Question

In four o'clock plants, the gene for red flower colour (R) is incompletely dominant over the gene for white flower colour (r), hence the plants heterozygous for flower colour (Rr) have pink flowers. What will be the ratio of offsprings in a cross between red flowers and pink flowers?

• A. 75% red flowers, 25% pink flowers
• B. All red flowers
• C. 50% red flowers, 50% pink flowers
• D. Red : pink : white : : 1 : 2 : 1

Answer 1

Answer: (C)

As Mendel, on crossing homozygous members for contrasting characters, the dominant trait is expressed in the heterozygous or hybrid condition. Incomplete dominance is a deviation of Mendel's law of dominance where the heterozygous individual instead of expressing the dominant trait, it expresses a trait which is a mix of the parent traits.
On crossing, red(RR) flower plant with white(rr) flower plant, the offspring flower is pink(Rr) flower.
When a red flower plant is crossed with pink flower plant we get:

	R	R
R	RR (Red)	RR (Red)
r	Rr (Pink)	Rr (Pink)

Genotype of $F_{1}$ - RR and Rr $$ 1:1
Phenotype of $F_{1}$ - Red and Pink $$ 1:1 (50% and 50%)