Codominance

Codominance

Codominance is a form of inheritance in which two different alleles for a genetic trait are both expressed. Unlike dominant and recessive alleles, where the dominant allele masks the expression of the recessive one, codominant alleles result in a phenotype that clearly shows both traits.

Mechanism of Codominance

In codominance, both alleles contribute equally and visibly to the organism's phenotype. This occurs because neither allele can mask the expression of the other. As a result, the heterozygous genotype exhibits characteristics of both alleles.

Example: ABO Blood Group System

One of the most well-known examples of codominance is the ABO blood group system. In this system, the alleles for blood type A (I^A) and blood type B (I^B) are codominant. Individuals with genotype I^AI^B have blood type AB, which means both A and B antigens are expressed on the surface of red blood cells.

Genetic Basis

Codominance occurs at the molecular level when both alleles produce functional proteins that are expressed in the phenotype. This is different from incomplete dominance, where the heterozygous phenotype is an intermediate of the two homozygous phenotypes.

Comparison with Other Inheritance Patterns

• Dominance: In dominance, one allele masks the expression of another. For example, in Mendelian inheritance, the dominant allele completely masks the recessive allele in the heterozygous condition.
• Incomplete Dominance: In incomplete dominance, the heterozygous phenotype is a blend of the two homozygous phenotypes. An example is the flower color in snapdragons, where red and white alleles produce pink flowers in the heterozygous state.

Importance in Medicine

Understanding codominance is crucial in genetics and medicine, particularly in blood transfusions and organ transplants. The ABO blood group system is a critical consideration in these medical procedures to prevent adverse reactions.

See Also

• Genetics
• Mendelian inheritance
• Incomplete dominance
• Blood type