Question

In Mirabilis jalapa , the percentage of plants having pink and red flowers would be ________ when pink flower plant is test crossed.

• A. 25% pink and 25% red
• B. 50% pink and 50% red
• C. 50% pink and 0% red
• D. 0% pink and 50% red

Answer 1

The correct option is B 50% pink and 50% red

Gamete	R	r
r	Rr- Pink flower	rr- White flower

Mirabilis jalapa is a plant showing incomplete dominance which means that when in F${}_1$ generation intermediate phenotype appears instead of the two parent phenotypes.

While, the test cross is defined as a cross between an F${}_1$ plant and the homozygous recessive parent.

So, for plants to be pink in Mirabilis jalapa the plant has to be Rr in genotype. (where R is dominant on r while RR gives Red color and rr gives white color flowers in a plant).

Desired cross: Rr x rr
So, the phenotype ratio is: 1:1::Pink flower:White flower

So, the correct answer is '50% pink and 50% red'.