Question

What is incomplete dominance? Write an example.

Answer 1

Hint: Incomplete dominance is a condition in which the presence of dominant genes in the genotype of an organism does not cover the effects marked due to the presence of a recessive allele completely.

Complete Step by Step Answer:
The cross performed by Gregor Mendel of the pea plants showed various kinds of genotypes that are present in the pool of results of the cross. The cross also showed that the presence of a dominant allele covers the effect of a recessive allele or in other words, it suppresses any trait of the recessive allele. Although that is not the case always. You see that heterozygous genes may show complete or incomplete dominance. In incomplete dominance, although the genes are heterogeneous the traits of both the alleles, viz. the dominant and the recessive alleles are visible. This is also shown in the cross that was performed by Mendel. Incomplete dominance can be seen in animals for example Andalusian fowl and the trait which is affected by incomplete dominance is the feather type. A white male fowl and a black female fowl produce an offspring that has blue colored feathers. That is the resultant phenotype belongs to neither of the parents.

Additional Information:
- In humans too incomplete dominance can be seen, the phenotype affected can be the nature of the hair, i.e., a parent with curly hair and another parent with straight hair can have a child having curly or wavy hair.

- The Tay-Sachs disease in humans also shows incomplete dominance.
- Rabbits also show incomplete dominance, i.e., the characteristics of the fur are affected by incomplete dominance. Two parents having short and long furs may have a child who has furs of medium length.
- Codominance can show the phenotype of both recessive and dominant but uniformly or equally.
- Codominance is also present in the humans having blood group AB, i.e., both the alleles for A and B have equal contribution to the physical traits.

Note:
- Codominance and incomplete dominance are two different phenomenons, you must be careful about that. Codominance is a special form of incomplete dominance in which the genes affect the trait uniformly.
- You must also note that Incomplete dominance or Codominance is seen in heterozygous genes only where there is a presence of both dominant and recessive genes.