The ability to roll the tongue (R) is determined by a dominant gene while the 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 their son cannot. Explain this by showing the genotypes of all three persons.
Both of the parents were heterozygous (Rr) for rolling their tongues where as their child inherited the recessive (r) from both parents and was (rr) he was in the 25% chance that would happen. The punnet square tells us there's a 25% chance the kid would be RR 50% Rr and 25% rr
These are the possible genotypes RR, Rr, Rr, rr
First 3 carries dominant gene for tongue rolling, so they can do it,
while the 4th genotype rr is homologous for recessive, and he/she can't
perform tongue rolling.
