If the ability to roll one’s tongue is dominant (r) and the inability to roll one’s tongue is recessive (r), what would the genotype be for someone who can not roll their tongue?

The correct answer is-

Genotype for someone who can not roll their tongue would be 'rr'.

As per the information given in the question, ability of rolling tongue is a dominant trait (depicted by capital letter allele R) and inability to roll is a recessive trait (depicted by small letter allele r).

Dominant trait is the one that masks the expression of the recessive trait.

The only possible genotype for the recessive trait would be rr (homozygous recessive).

As 'Rr' and 'RR' will exhibit the genotype for dominant trait due to the presence of dominant allele 'R' (rolling of tongue).

Thus, 'rr' is the right answer.