Heterozygous means that the father has one dominant gene for tongue-rolling, and one recessive gene for non-tongue-rolling. The mother is homozygous recessive, meaning she has two copies of the non-tongue-rolling gene.
This means that every child is guaranteed a non-rolling gene from their mother, and they have a 50% chance of inheriting a rolling gene from their father. Since the rolling gene is dominant, only one copy of the gene is required to show the trait, so the 50% of children with the rolling gene from their father will be able to roll their tongues.
The answer is 50% of offspring.
