Codominance Vs. Incomplete Dominance

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Codominance Vs. Incomplete Dominance

If you are confused about the difference between co-dominance and incomplete dominance, then refer to this article. Easy explanations regarding this subject have been covered in the following paragraphs.

The father of genetics, Gregor Mendel, came up with one of the greatest discoveries of all times. He discovered the Principle of Dominance, which helped to explain the genetic traits inherited by the progeny from its parents. He selected pea plants for his research that was based on dominant and recessive traits. These plant was easy to study, as the traits could be simply observed through the naked eye. Mendel was able to show dominance as the relationship between two alleles on a single gene, which are found in chromosomes. When an allele is able to mask the expression of another one, then it is said to be dominant. The allele that does not express itself is called recessive. This principle can be expressed in different ways like complete dominance, incomplete dominance, co-dominance, and pseudo-dominance. The play of genes is also responsible for the dominant and recessive traits in humans, which are very easily observed in the offspring of parents, who have different racial origins, or have come from different gene pools.

Difference Between Co-dominance and Incomplete Dominance

In the above paragraph, both the types of alleles present in a gene have been explained. These genes are inherited from the parents, and the one that is dominant expresses itself in the progeny.

What is Co-dominance in Genetics

The law of co-dominance, basically incorporates the existence of the alleles with each other in a simultaneous manner. This means that when there are two alleles, which share a co-dominant relationship, the progeny will express both alleles. For example, if a black cat (CbCb) is crossed with a brown cat (CrCr), the kittens (CbCr) will be either brown with black spots or stripes, or black with brown spots or stripes, i.e., tabby cat. This means that both colors are co-dominant in this case, and both the alleles are completely expressed, and the kittens show both colors at the same time.

Incomplete Dominance in Genetics

It is the expression of alleles that are neither dominant or recessive. These alleles mix together and result in the expression of a physical trait, which is a mixture of both the alleles. For example, when you cross a black mice (BB) with a white mice (WW), their progeny is gray in color (BW). These colors blend together and express the phenotype of both alleles. This type of dominance is similar to mixing paints. When you mix one color with another color, the result is a completely different color. Similarly, when one allele is mixed with another allele, they blend together to give rise to a new phenotype.

Thus, in short, it can be said that in co-dominance, the alleles express their individual traits simultaneously. In case of incomplete dominance, the alleles tend to blend in to give rise to an altogether new phenotype.

Examples of Co-dominance and Incomplete Dominance

Example 1

When one crosses a red snapdragon flower (RR) with a white snapdragon flower (WW), the result will be as follows:


will give rise to


The flowers show incomplete dominance as the red and white colors blend in and express a completely new color, i.e., pink.

Example 2

When a cream colored mare (CC) is paired with a brown colored horse (BB), it will result in a pony that is tan in color. This is an example incomplete dominance, where the alleles blend to form a new phenotype.


this results in an offspring that is tan in color


Example 3

When a red flower is crossed with a white flower, it results in flowers with red spots on white background, or white spots on red background.

R1R1 X R2R2

the resultant flowers are


This is an example of co-dominance where both red and white color are expressed in the resultant flowers.

Genes like to play around and express different phenotypes in a progeny, and hence, at times, it is very difficult to understand them. They are studied in the branch of genetics, for their ability to shape the destines of each human being; to be more specific, in human genetics. Most often. we observe complete dominance, where one allele completely takes over another allele.

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