Key Difference – Dominance vs Codominance
The concept of dominance was introduced by Gregor Mendel in 1865 after performing eight years of experiments with pea plants. Mendel explained that genes have a pair of alleles and an offspring receives one allele from the mother, and the other allele from the father and the traits are passed from one generation to the next generation. Dominance and codominance are relationships of the alleles of the genes when expressing the phenotypes. The key difference between dominance and codominance is that dominance is the masking effect of one allele over the other allele when the gene is in heterozygous state while the codominance is expressing the effects of both alleles independently without blending in heterozygous state.
CONTENTS
1. Overview and Key Difference
2. What is Dominance
3. What is Codominance
4. Side by Side Comparison – Dominance vs Codominance
5. Summary
What is Dominance?
Dominance is the key concept used by Gregor Mendel to explain the theory of inheritance. A gene is known to have two alleles: a dominant allele and a recessive allele. Dominance is a type of allele interaction in the heterozygous state, in which one allele of a gene if fully expressed and the effect of the second allele is masked, resulting in a phenotype which expresses the dominant trait. The allele which is expressed is known as the dominant allele while the allele which is subjected to suppression is known as a recessive allele of the gene. If an allele is dominant, one dominant allele is enough to express the dominant trait in the offspring.
Gregor Mendel described the law of dominance as, “An organism with alternate forms of a gene will express the form that is dominant”. When two individuals with heterozygous alleles are crossed with each other, it produces dominant and recessive phenotypes in 3:1 ratio.
Figure 01: Complete dominance
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. In heterozygous, both alleles are expressed fully and show the effects of the allele in the offspring independently. Neither allele suppresses the effect of the other in codominance. The final phenotype is neither dominant nor recessive. It is composed of a combination of both traits. Both alleles are manifested in the phenotype without mixing the individual effects. In the final phenotype, effects of the both alleles can be distinguished clearly in the codominance situation.
ABO blood group system can be explained as 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.
Figure 02: Codominance in Rhododendron
What is the difference between Dominance and Codominance?
Dominance vs Codominance |
|
| Dominance is a relationship between two alleles in which dominant allele suppresses the effect of recessive allele during the expression. | Codominance is a form of dominance in a heterozygous in which both alleles independently show the effect of the allele on the final phenotype. |
| Traits of Phenotype | |
| Effect of the dominant allele is shown in the phenotype. | Effects of both alleles are clear in the codominance. |
| Expression of Alleles | |
| One allele is expressed fully while the other allele is suppressed. | Both alleles are expressed fully in the codominance state. |
| Masking Effect | |
| One allele completely masks the effect of the other allele. | Neither allele completely masks the other. |
| Phenotype | |
| Phenotype is dominant. | Phenotype is neither dominant nor recessive. |
| Independence of the Allele | |
| Dominant allele works independently. | Both alleles work independently and equally. |
| Quantitative Effect | |
| Quantitative effect is present. | The quantitative effect is absent. |
Summary – Dominance vs Codominance
Dominance and codominance are two types of allelic relationships shown in the heterozygous state. Dominance is the situation in which dominant allele is fully expressed while suppressing the recessive allelic effect on the phenotype. Codominance is the situation in which both alleles work independently and express their effects in the phenotype without mixing the effects. This is the difference between dominance and codominance. In dominance, dominant allele is dominated while in the codominance neither allele is dominated.
References:
1. Ilona Miko. “Gregor Mendel and the Principles of Inheritance.” Nature News. Nature Publishing Group, 2008. Web. 19 Apr. 2017
2. Scoville, Heather. “Codominance – Evolution Definition.” ThoughtCo. N.p., n.d. Web. 19 Apr. 2017
Image Courtesy:
1. “Co-dominance Rhododendron” By darwin cruz – Flickr (CC BY 2.0) via Commons Wikimedia