Question

Which of the following is not the case of incomplete dominance?

• A. Inheritance of flower colour in Antirrhinum majus
• B. ABO blood groups in human
• C. Inheritance of flower colour in Mirabilis jalapa
• D. All of the above

Answer 1

The correct option is B ABO blood groups in human

The expression of flower colours in Mirabilis jalapa and Antirrhinum majus are controlled by alleles with incomplete dominance.

Both plants produce either red or white flowers. When the plant with red flowers is crossed with a plant bearing white flowers, the progeny will produce flowers of pink colour.

This expression is an intermediate of the two parental characteristics. This phenomenon is called incomplete dominance. This occurs because neither of the two alleles is completely dominant over the other. This results in a phenotype that is a combination of both.

ABO blood groups in humans are controlled by three alleles $I^A$, $I^B$ and i. Hence this is an example of multiple alleles.

Furthermore, the alleles $I^A$ and $I^B$are co-dominant. When an individual inherits both alleles $I^A$ and $I^B$ from their parents, their blood group is AB i.e. both alleles are expressed equally, together. ($I^A$ and $I^B$ alleles are responsible for the production of A and B types of sugars respectively).

Hence, a person of AB blood group has both A and B types of sugars on RBC.