What is the Difference Between Dominance and Codominance?

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Dominance and codominance are two types of genetic inheritance that can occur when an individual has two different alleles (forms of a gene) for a particular trait. The main difference between the two lies in how the alleles express themselves in the phenotype (physical appearance) of the individual.

Dominance:

  • Incomplete dominance: This occurs when a dominant allele does not completely mask the effects of the recessive allele. As a result, the phenotype of the offspring is a blend of the two parent phenotypes. For example, if a pea plant with a dominant allele for tallness (T) and a recessive allele for shortness (t) has a phenotype that is neither tall nor short, but in between.

Codominance:

  • In this case, both alleles are expressed in the phenotype of the individual, and neither allele is dominant or recessive over the other. For example, in the ABO blood group system, individuals with blood group ABO have both A and B alleles, but neither is dominant over the other. A person with such a blood type would exhibit both A and B antigens on their blood cells.

In summary, the key difference between dominance (incomplete dominance) and codominance is that in incomplete dominance, one allele is not completely dominant over the other, resulting in a blended phenotype. In contrast, codominance occurs when both alleles are expressed in the phenotype without being dominant or recessive.

Comparative Table: Dominance vs Codominance

Here is a table comparing the differences between dominance and codominance:

Feature Dominance Codominance
Definition Dominance refers to the situation where one allele is completely dominant over the other, resulting in the expression of only one trait. Codominance refers to the situation where both alleles are simultaneously expressed in the heterozygote, resulting in the expression of both traits.
Phenotype Expression In dominance, the dominant allele completely masks the expression of the recessive allele, leading to the expression of only one trait. In codominance, both alleles are expressed in the phenotype, resulting in a combination of the traits.
Blood Group Example Individuals with blood group OO exhibit dominance, as the O allele is completely dominant over the A and B alleles. Individuals with blood group AB exhibit codominance, as both A and B alleles are dominant in relation to O but not dominant against each other, resulting in the expression of both A and B traits.
Relationship Between Alleles In dominance, one allele is completely dominant over the other, leading to the expression of only one trait. In codominance, both alleles neither act as dominant or recessive over the other, resulting in the expression of both traits.
Hybrid Formation In dominance, a hybrid will not result in the formation of a new phenotype, as the dominant allele completely masks the expression of the recessive allele. In codominance, a hybrid will always result in a new phenotype, as both alleles are expressed in the phenotype, resulting in a combination of the traits.