Phenotype is the physical appearance of the organism, which is depicted by the genes. The genetic makeup of the organism is termed as genotype. Both genotype and phenotype are inter-dependent on each other. If the genotype changes, phenotype will change accordingly.
Gene is present in various forms and these forms are termed as alleles. Alleles are classified as dominant and recessive. When the phenotype of the organism is translated into the genotype, alleles are used.
Here, genotype of the tall plant could be either TT or Tt.
Genotype of short plant will be tt only. This is because short height is a recessive trait. It will be visible only when it is present in homozygous state, as in “tt”.