Given the allele for tall plants (T) is dominant to the allele for short plants (t), describ the phenotypes of the following genotypes. a) Tt
When an Allele is dominant that means that it will show in a phenotype over the recessive Allele, if present, in the genotype. Since the Allele for tall plants is dominant, it will show in the phenotype, even if a short allele is present. Thus a genotype of Tt will show tall plants, because the dominant "tall-plant" allele is present.
If you had Genotype TT, you would also have tall plants. If you had genotype tt, you would have short plants, since the dominant Tall-plant allele isn't present.