Codominance in plant inheritance occurs when both alleles of a gene are equally expressed in the heterozygous condition — meaning neither allele is dominant nor recessive, and both traits appear side by side in the offspring.
Unlike incomplete dominance (where traits blend), codominance results in both parental traits being visible together.
Example:
In Mirabilis jalapa (four o’clock plant), incomplete dominance gives pink flowers (a blend).
But in codominance, you might see both colors appearing together, such as red and white patches on the same flower.
Another example is seen in maize (corn) where the red and white colors of kernels are both expressed in a single ear — some kernels are red, and others are white.
In short:
- Codominance = both alleles are fully expressed.
- The heterozygote shows both traits distinctly, not blended.