Question

Plant, which does not obey Mendel's laws is

• A. Mirabilis jalapa
• B. Pisum sativum
• C. Iberis amara
  
• D. None of the above

Answer 1

The correct option is A Mirabilis jalapa

It is a type of intragenic (or interallellic) interaction, where both the alleles of a given trait express as a blend (mixture) as against a normal Mendelian pattern, where one allele is dominant over the other. As a resulting of this blending, an intermediate character is expressed. This situation occurs due to the fact that the dominant gene is not in a position to completely suppress the expression of recessive gene. With the result, the heterozygous offspring will be phenotypically and genotypically different from either of the homozygous parent. Following are the two familiar examples of incomplete dominance.

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.