Let's make the alleles Tt, where T is dominant (tongue rolling) and t is recessive (inability to tongue roll).
The heterozygous tongue roller would be Tt and the non tongue roller would be tt. Putting them in a punnet square (refer to attachment), the chances that their child will be a non tongue roller would be a 50% chance.
Tt: 2/4 = 50%
tt: 2/4 = 50%
The heterozygous tongue roller would be Tt and the non tongue roller would be tt. Putting them in a punnet square (refer to attachment), the chances that their child will be a non tongue roller would be a 50% chance.
Tt: 2/4 = 50%
tt: 2/4 = 50%