Question

The Ability to roll the tongue is determined by dominant gene while the recessive gene results in the inability to roll the tongue.
A man and his wife can both roll their tongues and are surprised to find there son cannot. Explain this by showing the genotype of all three persons.

Answer 1

The wife and husband are heterozygous, therefore, they have one dominate allele and one recessive allele. The little boy inherited both recessive alleles so he can't roll his tongue.
T = Dominate allele
t = recessive allele

Wife : Tt
Husband: Tt
Boy: tt