Question

how do we know which among the traits in incomplete dominance is dominant

Answer 1

Answer:

If the phenotype was "red" then r allele is dominant to b. If the phenotype was "blue" then b allele is dominant to r. If the phenotype was "purple" then these alleles show incomplete dominance. If the phenotype had some types of cells "red" and others "blue" then these alleles show codominance.