Difference Between Incomplete Dominance and Codominance

What is Incomplete Dominance?

Incomplete dominance is a form of Gene interaction in which both alleles of a gene at a locus are partially expressed, often resulting in an intermediate or different phenotype. It is also known as partial dominance.

For eg., in roses, the allele for red colour is dominant over the allele for white colour. But, the heterozygous flowers with both the alleles are pink in colour.


Mechanism of Incomplete Dominance

Incomplete dominance occurs because neither of the 2 alleles is totally dominant over the opposite. This results in a phenotype that is a combination of both.

Gregor Mendel conducted experiments on pea plants. He studied seven characters with contrasting traits and all of them showed a similar pattern of inheritance. Based on this, he generalized the law of inheritance.

Later, researchers repeated Mendel’s experiment on other plants. Shockingly, they noted that the F1 Generation showed variation from the usual pattern of inheritance. The monohybrid cross resulted in F1 Progeny which didn’t show any resemblance to either of the parents, but an intermediate progeny.


Concept of Dominance

In genetics, Dominance is a relationship between alleles of one gene. In order to understand the concept of the dominance of alleles, we need to know more about genes.

So far we know that genes are a hereditary unit in organisms which exist as a pair of alleles in diploid organisms. These pairs of alleles may or may not be similar. That is, a heterozygous gene has two dissimilar pairs of alleles while homozygous have identical ones.

Heterozygous alleles carry different information on traits. When we say one trait is dominant over the opposite , there are often two reasons:

  • either it is non-functional, or

  • is less active than the normal allele


Incomplete Dominance and Codominance

Incomplete dominance and codominance are different from one another .

In codominance, both the alleles present on a gene are expressed in the phenotype. A flower showing codominance will have patches of red and white instead of a uniformly pink flower.

In incomplete dominance, the F2 generation from heterozygous plants will have a ratio of 1:2:1 with the phenotypes red, white and spotted flowers.

The humans with AB blood type also show codominance where the alleles for both blood types A and B are expressed.


Examples of Incomplete Dominance

Examples of incomplete dominance are mentioned below:


In Humans

The child of parents each with curly hair and straight hair will always have wavy hair. Carriers of Tay-Sachs disease exhibit incomplete dominance.


In Other Animals

In its feature colors, the Andalusian chicken shows incomplete dominance When the rabbits with long and short furs are bred, the offspring produced will have medium fur length.


Difference Between Incomplete Dominance and Co-dominance 

Incomplete Dominance 

Co-dominance 

2 parent phenotypes are expressed together in their offspring

2 parents blend together to create a new phenotype for their offspring

The two alleles neither act as dominant or recessive over the other

One allele is not completely dominant over the other

Both the alleles blend equally and show the traits in their offspring

Both alleles blend, however only one of the two is noticeable in the offspring

A hybrid will not result in the formation of a new phenotype

A hybrid will always result in a new phenotype

Individuals with blood group ABO exhibit Codominance. A and B are dominant in relation to O, however, they are not dominant against each other.

Snapdragon, Antirrhinum majus (pink flowers are resultant when crossed between a homozygous red flower and a homozygous white flower)

FAQ (Frequently Asked Questions)

Q1. What is Incomplete Dominance ?

Ans: Incomplete dominance is a form of Gene interaction in which both alleles of a gene at a locus are partially expressed, often resulting in an intermediate or different phenotype. It is also known as partial dominance.

For eg., in roses, the allele for red colour is dominant over the allele for white colour. But, the heterozygous flowers with both the alleles are pink in colour.

Q2. What is the Concept of Dominance?

Ans: In genetics, Dominance is a relationship between alleles of one gene. In order to understand the concept of the dominance of alleles, we need to know more about genes.

So far we know that genes are a hereditary unit in organisms which exist as a pair of alleles in diploid organisms. These pair of alleles may or may not be similar. That is, a heterozygous gene has two dissimilar pairs of alleles while homozygous have identical ones.

Heterozygous alleles carry different information on traits. When we say one trait is dominant over the opposite , there are often two reasons:

  • either it is non-functional, or

  • is less active than the normal allele

Q3. Give Examples of Incomplete Dominance in Humans and Animals

Ans: Examples of incomplete dominance are mentioned below:


In Humans

The child of parents each with curly hair and straight hair will always have wavy hair. Carriers of Tay-Sachs disease exhibit incomplete dominance.


In Other Animals

In its feature colors, the Andalusian chicken shows incomplete dominance When the rabbits with long and short furs are bred, the offsprings produced will have medium fur length.