Codominance Vs. Incomplete Dominance

The father of genetics, Gregor Mendel came up with one of the greatest discoveries of all time. He discovered the Principle of Dominance that helped explain the genetic traits inherited by the progeny from its parents. He picked up pea plants for his study based on dominant and recessive traits. The pea plant was easy to study as the traits could be easily 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 one allele is able to mask the expression of another allele then it is said to be dominant. The allele that does not express itself is called recessive. Dominance can be expressed in different ways like complete dominance, incomplete dominance, codominance and pseudominance. The play of genes is also responsible for the dominant and recessive traits in humans which are very easily observable in offspring of parents who have different racial origins or come from different gene pools.

Difference Between Codominance and Incomplete Dominance

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

What is Codominance in Genetics
Codominance basically means existing together. This means when there are two alleles that share a codominant relationship, progeny will express both alleles . For example, if a black cat (C^bC^b) is crossed with a brown cat (C^rC^r), the kittens (C^bC^r) will be either brown with black spots or stripes or black with brown spots or stripes, that is, tabby cat. This means both the colors are codominant in this case. Both alleles are completely expressed and the kittens show both colors at the same time.

Incomplete Dominance in Genetics
What is incomplete dominance? It is the expression of alleles that are neither dominant or recessive. These alleles mix together and result in expression of a physical trait that is a mixture of the two alleles. For example, when you cross a black mice (BB) with a white mice (WW), the progeny of these mice is gray in color (BW). The 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.

As you can see, in codominance 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. Let us know more through examples to understand the additional differences between these two.

Examples of Codominance 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:

RR X WW

will give rise to

RW

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

Example 2

When 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 incomplete dominance example where the alleles blend to give a new phenotype.

CC X BB

this results in an offspring that is tan in color

CB

Example # 3
When a red flower is crossed with 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

R¹R²

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

Genes, like to play around and express different phenotypes in progeny. It is very difficult understanding genes at times. For their ability to shape the destines of each human being they are studied in the branch of genetics, to be more specific in human genetics. Most often we observe complete dominance, where one allele completely takes over another allele. Hope, the above explanation has helped you understand the difference between codominance and incomplete dominance sufficiently.