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 phenotypic ratio in $F_2$ generation when $F_1$ (Rr) was self-pollinated?

1 : 2 : 1

The correct answer is Option (2) → 1 : 2 : 1.

In snapdragon flower colour, the inheritance pattern is incomplete dominance, not complete dominance. When a true-breeding Red plant (RR) is crossed with a true-breeding White plant (rr), the F₁ generation becomes Pink (Rr) because neither allele is fully dominant.

When the F₁ (Pink, Rr) is self-pollinated (Rr × Rr), the F₂ generation produces three genotypes:

• RR → Red

• Rr → Pink

• rr → White

Thus, the phenotypic ratio becomes 1 Red : 2 Pink : 1 White, which is 1 : 2 : 1.

Why 3:1 is incorrect

A 3 : 1 ratio occurs only in complete dominance, where the heterozygous individual shows the dominant trait fully. Here, the heterozygous plant is visibly different (Pink), so all three phenotypes appear separately.

Thus, the correct answer, that is the phenotypic ratio is 1 Red : 2 Pink : 1 White, which is 1 : 2 : 1.