What is co-dominance in genetics?

Co-dominance in genetics refers to a situation where both alleles in a heterozygous organism are fully expressed, resulting in a phenotype that displays characteristics of both alleles simultaneously. This means that neither allele masks the other; instead, both contribute equally and visibly to the organism’s appearance.

For example, in the case of blood type inheritance, individuals with one allele for type A blood and one allele for type B blood will express type AB blood, showcasing the traits from both parents. Such a display is distinct from other forms of dominance in genetics, such as complete dominance, where one allele completely overshadows the other, or incomplete dominance, where a mix of traits is seen but not fully expressed.

In summary, the defining characteristic of co-dominance is the simultaneous and equal expression of both alleles in the phenotype, leading to a unique expression that neither completely dominates over the other.