Question

In Mirabilis jalapa, RR, Rr and rr determine red, pink and white colour respectively. When F${}_1$ hybrid of RR and rr was crossed with dominant parent, the ratio produced is

• A. All red
• B. 1 Red : 1 Pink
• C. All white
• D. 3 Pink : 2 white

Answer 1

Answer: (B)

1 Red : 1 Pink

Incomplete dominance is the condition when none of the factors of a gene is dominant, the phenotype of the heterozygous dominant individual is a blend of dominant and recessive traits. For example, flower color in Mirabilis jalapa shows incomplete dominance. A red allele is incompletely dominant over white colour allele; thus “RR” genotype produce red flowers while “rr” gives white flowers but “Rr” produce less half the pigment than “RR” genotypes and gives pink flowers.

Parent generation : Rr (hybrid of RR and rr) x RR (dominant parent)

Gametes Rr ----> RR	R	r
R	RR (red flower)	Rr (pink flower)

Phenotypic ratio = 1 red : 1 pink; option B is the correct answer.