Incomplete Dominance vs Codominance: Difference and Comparison

Gregor John Mendel proposed the Inheritance and Dominance laws, later, the term “Incomplete dominance” was coined by Carl Correns, a German Botanist. A heterozygous individual is produced by both the alleles of a trait.

Dominant and recessive characters are expressed in incomplete dominance as well as codominance.

Key Takeaways

1. In incomplete dominance, the offspring display a blend of both parent traits, while in codominance, both traits appear distinctly in the offspring.
2. Incomplete dominance creates a new phenotype, whereas codominance results in a combination of existing phenotypes.
3. Incomplete dominance involves one allele not completely dominating the other, while codominance features both alleles being expressed equally.

Incomplete Dominance vs Codominance

Incomplete dominance occurs when the heterozygote displays an intermediate phenotype between the two homozygotes, where, neither allele is dominant over the other. In codominance, both alleles are expressed equally in the heterozygote, resulting in a phenotype that exhibits traits of both alleles.

Incomplete dominance occurs when the offspring has an intermediate phenotype of both the parents. The input expressed by the parents is distinct in the progeny.

When a person is heterozygous for a gene, he or she possesses two distinct alleles, but this isn’t necessarily enough to produce an intermediate phenotype. Incomplete dominance can be caused by one gene hiding the phenotype of the other one.

Codominance results when the phenotypes of the alleles are in almost equal values present in the offspring. A popular example of this type is the ABO blood group.

Mendel’s model can be used to predict the outcomes of co-dominance crossings of the alleles. The F1 generation will have a genotypic ratio of 1:2:1.

Codominance is an interaction between two genes in which both genes exhibit and express their traits at the same time, according to the law of codominance.

Comparison Table

Parameters Of Comparison	Incomplete Dominance	Codominance
Definition	Incomplete dominance is seen in heterozygotes where the dominant trait does not overcome the recessive character.	Codominance is seen in heterozygotes where the dominant and recessive traits are expressed in their characteristics.
Phenotype expressed	Intermediate offspring	Independent offspring
Dominance	One of the allele’s traits gets dominant over another	Both of the alleles don’t act as dominant or recessive over another
Phenotype	The phenotypes of the parents cannot be seen in the offspring	The phenotypes of the parents can be seen in the offspring
Examples	Crossing of red flowers	ABO Blood group

What is Incomplete Dominance?

Incomplete dominance is the result of two real parents crossing to form an intermediate offspring. Furthermore, also known as intermediate dominance or incomplete dominance.

The variations of the alleles have no dominant or recessive characters whereas the dominant allele has the least ratio in incomplete dominance.

For instance, the pink shade of blossoming flowers, the state of hairs, hand sizes, the colour of eyes and voice pitches in people.

Gregor John Mendel was the first to give discover dominance term and explained by a pea plant experiment.

As previously stated, incomplete dominance is a form of partial dominance in which the phenotype is intermediate between the genotypes of dominant and recessive alleles.

Due to the incomplete dominance, the resultant progeny will possess a pink colour trait despite the red dominant and white colours of the allele. It is genetically significant to explain the truth that separate alleles may exist.

We can see the existence of incomplete dominance in red and white snapdragon flowers. It occurs when the dominant allele is unable to entirely dominate the recessive gene, resulting in a phenotype that is a mix of both the alleles.

The law of Dominance was developed by Mendel showing that the two alleles are both of dominant and recessive character, and recessive character is influenced by dominant character.

What is Codominance?

In this type, both the alleles are independent of the expressions in a single phenotype. It’s a connection between alleles of a gene that is similar to a dominance relationship.

Both alleles are addressed in heterozygous individuals and have separate impacts on their progeny. In codominance, the alleles don’t reduce the influence of one another and the final phenotype is not either dominant or recessive.

The impacts of both the alleles are evident separately in the phenotypic gene. Codominance is a kind of inheritance in which both the alleles of a gene pair are completely expressed in a heterozygote.

So, the mix of parents’ phenotypes is the result found in their offspring’s phenotype. The trait is popularly studied by the white-spotted red blossom flower in plants and the black-white coated mammals in animals.

A tool named “Punnett square” is used to determine the codominant type of trait.

An example of codominance is the ABO blood group system. The alleles A and B are mutually dominant to each other. As a result, blood group AB does not fall under any of the two categories (i.e. Blood group A and Blood group B).

Due to the codominance between the two blood groups A and B function as distinct blood groups. Beta-thalassemia minor with a mutant haemoglobin beta-chain is an example of codominance.

Main Differences Between Incomplete Dominance and Codominance

1. The main difference between incomplete dominance and codominance is that incomplete dominance is a type wherein both the alleles partially express their phenotypes to the offspring whereas in codominance both the alleles are given in the phenotype of their offspring.
2. Incomplete dominance has no dominant or recessive characters on each other. Codominance does not completely dominate others.
3. The phenotypes of both the alleles are equally mixed and pass on the traits to their progeny. While in codominance, the alleles mix with each other but only one of them is apparent in the offspring.
4. The hybrids are of a phenotype will not occur in incomplete dominance whereas the hybrid of a phenotype will take place of the phenotype in codominance.
5. An example of incomplete dominance is the ABO type of blood group and, the crossing of the red and white flower is an example of codominance.

References

1. https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1007019
2. https://journals.sagepub.com/doi/abs/10.1177/03635465030310021101