If assuming PTC as a simple gene trait what other genotype would you select to put in this missing genotype box that could result in this phenotype, why?

The missing box will have genotype Tt

The phenotype will be tasters for PTC as TT, Tt

Explanation:

The taste of PTC is determined by the alleles on the PTC gene. It is a dominant trait. Those who are able to taste PTC have dominant alleles of TT (Homozygous or Tt Heterozygous).

Those having recessive gene tt are said to be non-tasters.

Those with the dominant allele in their PTC gene will find the taste of PTC bitter.

Those with the recessive allele in their PTC gene will find the taste of PTC as tasteless.

Thus genetic make-up of the individual decides their taste. The Phenotype can be either tasters or non-tasters.

TT, Tt (tasters)

tt ( non-tasters)

This follows Mendel's Law of Dominance.