Read the following passage carefully.

MONOHYBRID CROSS

The inheritance of flower color in the dog flower (Snapdragon or Antirrhinum sp.) can be understood by crossbreeding between true-breeding red-flowered (RR) and true-breeding white-flowered plants (rr). When they were crossed, $F_1$ (Rr) was pink. When $F_1$ was self-pollinated, the $F_2$ results were Red, Pink and White. Here the genotype ratios were exactly as expected, but the phenotype ratios have been changed. What happened was that R was not completely dominant over r and this made it possible to distinguish Rr as pink from RR (Red) and rr (White).

What was the expected phenotypic ratio in any Mendelian monohybrid cross that had changed when $F_1$ (Rr) was self- pollinated in this cross?

3 : 1

The correct answer is Option (3) → 3 : 1    

We are talking about a Mendelian monohybrid cross.

• Parent cross: RR × rr
  → F₁ all Rr (heterozygous).

• Then, F₁ self-pollination: Rr × Rr

The genotypic ratio = 1 RR : 2 Rr : 1 rr

The phenotypic ratio (if R is dominant, r is recessive) = 3 dominant : 1 recessive 

So, phenotypic ratio, the answer is 3 : 1