The traits of the potato are encoded either by a genotype TTEE, TtEe, or any combination involving a uppercase letter (dominant allele) an lower case letter. These traits have a different allele (that is, the recessive trait) so, the best way to prove wether the potato is a dominant homozygote or has any heterozygote allele, will be to cross with the recessive version of its alleles, that is a --> ttee - sticking out tongue/no ears - ´potato. If the potato is TTEE (dominant homozygote) its offspring will have the same traits, that is, smiling and two eared. But, if it has a heterozgote allele (either Tt, Ee or both, TtEe) it will have in its progeny individuals with the recessive trait, that is, either sticking tonge -ttEe-, no ears - Ttee, or both -ttee-.