A phenotype that results from a dominant allele must have at least ___dominant alleles present in the presents

A phenotype that results from a dominant allele must have at least one dominant alleles present in the presents. 

Explanation: In pea plant ( Pisum sativum ) tallness is dominant over dwarfness.  Dominant allele is written as T and recessive allele is written as t.

A plant has two alleles for each trait. According to Mendel's law of dominance, when two alternative alleles are present together, the dominant allele expresses itself in phenotype and the recessive allele, though present is not able to express in phenotype.

Recessive trait can appear in phenotype if both recessive alleles are present together, i.e. plant will be dwarf if having genotype tt (homozygous)

Plant will be tall whether it has two dominant alleles together TT(homozygous) or only one dominant allele Tt (heterozygous).

Thus only one dominant allele is sufficient for the dominant trait to appear in phenotype.