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?

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

Tardigrade Admin · Accepted Answer

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%)

Q. 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?

75% red flowers, 25% pink flowers

All red flowers

50% red flowers, 50% pink flowers

Red : pink : white : : 1 : 2 : 1