Answer: The percentage of the offspring will be phenotypic tongue-curlers is 75% and the genotypic ratio is 1TT : 2Tt : 1tt
Explanation: Since tongue-curling in humans is a dominant genetic trait (T), then non tongue-curling is recessive trait and is represented as (t).
A man and woman who are heterozygous for tongue-curling will have genotype Tt. A cross between two heterozygous individuals will produce four offsprings, Tt x Tt = TT, Tt, Tt and tt.
The genotype ratio is 1TT : 2Tt : 1tt.
Since (T) is dominant, genotypes TT and Tt will manifest phenotypically as tongue-curling, while tt will manifest phenotypically as non tongue-curling.
Since three out of four offsprings are phenotypic tongue-curlers, the percentage of the offspring that are tongue-curlers is 3/4 x 100 = 75%
See the attached punnet square for more information