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 will be the genotypic ratio in $F_2$ generation when $F_1$ (Rr) was self-pollinated?

1 : 2 : 1

The correct answer is Option (4) → 1 : 2 : 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, genotypic ratio = 1 : 2 : 1