Phenotype is the physical appearance
Genotype is the traits in letters.
lets say green eyes...
having the gene GG, Gg, except gg will yield green eyes
so, if you see someone with green eyes, he/she must either have two dominant trait or 1 dominant and 1 recessive trait. Since you gave to us that an organism expresses a recessive phenotype, you can automatically tell that the person will have 1 dominant and 1 recessive, or Gg.
However, if that is not given, you wont be able to tell the genotype based on looking at a person.
