The key difference between codominance and multiple alleles is that codominance is expressing the effects of both alleles independently, without blending in the heterozygous state, while multiple alleles refer to the state of a trait that has more than two different alleles.
Generally, each gene comes with two different alleles. One is a dominant allele while the other is a recessive allele. According to Mendelian inheritance, dominant allele expresses its phenotype while suppressing the recessive allele in the heterozygous state. However, some genes have three or more different alleles for one trait. They are called multiple alleles. Moreover, codominance is a non-Mendelian inheritance. In this phenomenon, offspring receives both parent genes as a combination of both the genes. Therefore, both genes are expressed equally in the offspring.
CONTENTS
1. Overview and Key Difference
2. What is Codominance
3. What are Multiple Alleles
4. Similarities Between Codominance and Multiple Alleles
5. Side by Side Comparison – Codominance vs Multiple Alleles in Tabular Form
6. Summary
What is Codominance?
Codominance is the expression of the effects of both alleles independently in one phenotype. It is a kind of a dominance relationship between alleles of a gene. Moreover, it is a type of non-Mendelian inheritance. In heterozygous state, both alleles are expressed fully and show the effect of the allele in the offspring independently. Neither allele suppresses the effect of the other allele in codominance. Hence, the final phenotype is neither dominant nor recessive. Instead, it comprises the combination of both traits. Both alleles manifest the phenotype with its effect without mixing the individual effects. In the final phenotype, the effects of both alleles can be distinguished clearly when the codominance situation. Furthermore, there is no quantitative effect in codominance.
Figure 01: Codominance
ABO blood group system is an example for codominance. Allele A and allele B are codominant to each other. Hence, blood group AB is neither A nor B. It serves as a separate blood group because of the codominance between A and B. Another classic example of codominance is the tabby cat. When pure black cats and brown cats mate with each other, the 1st filial generation will consist of kittens (tabby cats) which are black and having brown stripes or spots or vice versa. Codominance can also be observed among the Shorthorn cattle.
What are Multiple Alleles?
If a trait has more than two different alleles, we call them multiple alleles. In other words, multiple alleles are the three or more different alleles that code for a particular trait. Human ABO blood group system has three alleles. They are IA, IB and i. These three alleles create four different phenotypes as A blood group, B blood group, AB blood group and O blood group. Therefore, multiple alleles may be present at the population level. Different individuals in the population may have different pairs of these alleles.
Figure 02: Multiple Alleles
What are the Similarities Between Codominance and Multiple Alleles?
- Human ABO blood group system has multiple alleles, and it shows codominance.
- Multiple alleles and codominance do not obey Mendelian inheritance.
What is the Difference Between Codominance and Multiple Alleles?
Codominance is the condition where offspring receives a mixture of characteristics of both parental genes, irrespective of dominant or recessive genes. In contrast, multiple alleles are three or more than three different alleles that a particular trait has. So, this is the key difference between codominance and multiple alleles.
Summary – Codominance vs Multiple Alleles
Alleles are different versions of genes. Generally, there are two alleles existing for each gene. Sometime, there may be three or more alleles for one trait at the population level. We call this situation multiple alleles. In codominance, offspring receives a mixture of characteristics of both parental genes, irrespective of the dominant and recessive genes. This summarizes the difference between codominance and multiple alleles.