what is co-dominance?

Co-dominance is when two alleles are expressed equally in the phenotype in the heterozygote. For example, plants that are homozygous for one allele may be red and plants that are homozygous for another alleles may be white. If these alleles are co-dominant, then heterozygotes will be pink, as both alleles are expressed and there is enough red pigment to give the flowers a pink colour.