Final answer:
For two heterozygous parents for the tongue-curling trait, there is a 75% chance their child will be able to curl their tongue, as determined by a Punnett square considering Mendelian genetics.
Step-by-step explanation:
The likelihood that two heterozygous parents for the tongue-curling trait (represented by the allele t) will have a child able to curl their tongue can be determined using a Punnett square. Since tongue-curling is a dominant trait and both parents are heterozygous (Tt), the possible genotypes of their offspring are TT, Tt, Tt, and tt.
A child can curl their tongue if they have at least one dominant allele (T), which is possible in three out of the four genotype combinations (TT, Tt, Tt). Therefore, the probability of their child being able to curl their tongue is 75%.
By applying the principles of Mendelian genetics, the offspring of two heterozygous parents have a 25% chance of being homozygous recessive (tt) and unable to curl their tongue, and a 75% chance of being either homozygous dominant (TT) or heterozygous (Tt) and able to curl their tongue.
It's important to note that each child's genetic outcome is independent of the others, consistent with Mendel's Law of Independent Assortment.