The phenotypic and genotypic ratios of the $F_2$ generation are similar in which of the following cases?

The correct option is A Incomplete dominance
Incomplete dominance is a phenomenon where none of the two contrasting alleles of the gene is dominant. This results in the intermediate phenotype in the $F_1$ hybrid due to the blending of the alleles.

Consider that the pure breed of the snapdragon plant with red flowers has RR pair of alleles and that for the white flowers has rr alleles.

When true-breeding red (RR) and white (rr) flowered plants of snapdragon were crossed, the plants of the $F_1$­ generation produced pink-coloured flowers with Rr pair of alleles.

When the $F_1$ progeny undergoes self-pollination, the resulting $F_2$ generation has plants with red (RR), pink (Rr) and white (rr) flowers in the ratio of 1 : 2 : 1.


Recall that the genotypic ratio of $F_2$ generation in the monohybrid cross by Mendel also gave the same ratio of
1 : 2 : 1.

However, the phenotypic ratio has changed from 3 : 1 to 1 : 2 : 1.

The reason for this variation is the incomplete dominance of the allele R over the allele r. This led to the blending of colour in flowers.

Hence, phenotypic and genotypic ratios of the $F_2$ generation are similar in incomplete dominance.

The phenotypic and genotypic ratios of the Mendelian monohybrid cross are 3 : 1 and 1 : 2 : 1 respectively.

For the Mendelian dihybrid cross, the phenotypic and genotypic ratios are 9 : 3 : 3 : 1 and 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1 respectively.