Co-dominance is a genetic phenomenon where two different alleles are expressed equally in a heterozygous individual. This means that both traits associated with the alleles are visible in the organism. For example, in blood type, individuals with one allele for type A and one for type B will have type AB blood, showing both traits simultaneously. In co-dominance, neither allele is dominant or recessive, allowing for a blend of characteristics. This can be observed in certain flower colors, where a plant with one allele for red petals and another for white petals may produce flowers with both red and white patches, showcasing the distinct traits of each allele.