Question

In case of incomplete dominance, the monohybrid ratio of phenotypes in F${}_2$ generation is

• A. 1:2:1
• B. 3:1:1
• C. 9:3:3:1
• D. 2:3:1

Answer 1

The correct option is A 1:2:1

Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele. This results in a third phenotype in which the expressed physical trait is a combination of the dominant and recessive phenotypes. Incomplete dominance is seen in cross-pollination experiments between red and white snapdragon plants. The allele that produces the red color (R) is not completely expressed over the recessive allele that produces the white color (r). The resulting offspring are pink. The genotypes are: (RR) Red, (rr) White, and (Rr) Pink.
In the plant Mirabilis jalapa, commonly called as four o'clock plant, the inheritance of flower colour is an example for incomplete dominance. The plant produces two types of flowers red coloured and white coloured. This condition is an example for a pair of contrasting characters. When a plant which is homozygous for red flowers (AA) is crossed with a plant which is homozygous for white flowers (aa), the plants of the F${}_1$ generation produce pink flowers which is a blend of red and white condition. This result clearly indicates that neither red flowered condition nor white flowered condition is dominant. However, when two hybrid plants with pink flowers (Aa) are crossed, the F${}_2$ generation plants show red flowered, pink flowered and white flowered condition in the ratio 1:2:1. This ratio is very much in accordance with the law of segregation.