Phenotype are the traits an organism expresses. Dominant alleles only need one copy of that allele to be expressed. Therefore, if T represents the allele in pea plants for tall which is dominant, and t represents the allele for short height which is recessive, a pea plant with TT or Tt will both have a tall phenotype. A recessive allele when paired with a dominant allele, remains hidden. To express a recessive trait, an organism must have two recessive alleles. If a pea plant has a genotype-- tt, then this pea plant would have a short phenotype.