In a plant, r+ and q+ genes encode for a regulatory and a structural protein, respectively. These genes are responsible for blue color of flower. Mutation in either of the genes leads to white flowers, which is a recessive character. The two genes assort independently.

When two homozygous white-flowered plants are crossed, the F₁ plants have blue colored flowers. If the F₁ plant is backcrossed, the progeny will have plants with blue and white flowers in the ratio of:

Correct option is B

Explanation-

Given Information:
There are two genes, r⁺ and g⁺ and both are needed for blue flower color. ​Mutation (loss) in either gene leads to white flowers (recessive trait).
                r⁺ → regulatory protein
                g⁺ → structural protein
The genes assort independently.
Cross 1:
Two homozygous white-flowered parents are crossed:
                          So one parent must be r⁺r⁺ gg (functional regulatory, mutant structural)
                          Other must be rr g⁺g⁺ (mutant regulatory, functional structural)
Their F₁ progeny: genotype = r⁺r g⁺g
This has one copy of each functional gene → blue flowers
Backcross:
                          F₁ (r⁺r g⁺g — blue) is backcrossed with both white-flowered parents.
Let’s say we backcross with either parent, say r⁺r⁺ gg or rr g⁺g⁺.
We need to find the phenotypic ratio (blue : white flowers).

Backcrossing with white parent (e.g., r⁺r⁺ gg)
 r⁺r⁺ gg (white) as the parent for backcross.
F₁: r⁺r g⁺g
Parent: r⁺r⁺ gg

Result- 

r⁺r⁺ g⁺g → blue
r⁺r⁺ gg → white
r⁺r g⁺g → blue
r⁺r gg → white
Out of 4 combinations -  2 genotypes are blue  and  2 are white

Final Ratio = 1 (blue) : 1 (white)
So, the correct answer is option B-  1:1