When can the genotype be readily determined from the phenotype in the case of complete dominance?

Question

Also in the case of incomplete dominance and in the case of codominance

Answer 1

Complete dominance: the recessive phenotype is the only one you can be sure about. Recessive is bb; dominant could be either BB or Bb.

Incomplete and codominance: each of the possible genotypes have their own associated physical appearance or phenotype. So all the genotypes can be determined from the phenotype.

Answer 2

Well if it's complete dominance the genotype must be AA (or what ever letter is being used).
In incomplete dominance it would have to be heterozygous, but express a mixture between the two alleles (ie. red flower is dominant, white is recessive so pink is incomplete dominance)
Codominance, think blood typing, AB is a perfect example
(both alleles *both are dominant* are expressed)