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?

3 : 1

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

When F1 (Rr) plants are self-pollinated, they will produce the following gametes:

• R (dominant allele)

• r (recessive allele)

The self-pollination of F1 (Rr) results in the following combinations in the F2 generation:

• RR (homozygous dominant)

• Rr (heterozygous)

• rR (heterozygous)

• rr (homozygous recessive)

This results in a phenotypic ratio where:

• RR and Rr will show the dominant phenotype (since R is dominant).

• rr will show the recessive phenotype.

Thus, the phenotypic ratio will be: 3: 1