Codominance Definition Biology

Explore the fascinating world of codominance in biology, where two alleles are expressed equally. Learn about examples, case studies, and the importance of understanding this genetic phenomenon.

Introduction to Codominance

Codominance is a term used in biology to describe a genetic phenomenon where two different alleles for a gene are both expressed, resulting in a phenotypic trait that shows both alleles equally. This concept plays a crucial role in understanding inheritance patterns and genetic diversity.

Understanding Codominance

In codominance, neither allele is dominant or recessive, and both are fully expressed in the heterozygous genotype. This results in a phenotype that exhibits characteristics of both alleles, rather than a blended or intermediate trait.

Examples of Codominance

One classic example of codominance is the ABO blood group system. In this system, the alleles for blood type A and blood type B are codominant, leading to individuals with blood type AB expressing both A and B antigens on their red blood cells.

  • ABO blood group system
  • Speckled and patched flower patterns
  • Feathers of poultry

Case Studies on Codominance

A study of flower color in snapdragons found that the alleles for red and white flower colors were codominant. This led to snapdragons with pink flowers, where both red and white pigments were expressed simultaneously in the same plant.

Statistics on Codominance

Research on human genetics has shown that codominance plays a role in various traits, such as skin color, hair color, and eye color. Understanding codominance helps in predicting the phenotypic outcomes of genetic crosses and designing breeding programs for desired traits.


Codominance is a critical concept in biology that highlights the intricate interactions between different alleles and their impact on phenotypic traits. By studying codominance, scientists can gain insights into the complexity of genetic inheritance and the diversity of living organisms.

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