The ability to roll your tongue is determined by a dominant gene (R) while recessive gene results in the inability to roll the tongue (r). A man and his wife can both roll their tongues and are surprised to find that thier son cannot. Explain this by showing the genotypes of all three persons
The genotypes of the parents would both be Aa or heterogeneous. Therefore, based on a punnet square, there is a 25% chance that the offspring would have the genotype aa or homogeneous recessive, which occurred.
