In humans, the ability to roll up the sides of the tongue into a U-shape is controlled by one gene. Ability to roll the tongue is dominant to the inability to roll it. If two people who can roll their tongues each had one parent who could not, what is the probability that they will have a child who cannot roll his/her tongue

25%

Explanation:

male                                

can roll tongue     -     cannot roll tongue

female

can roll tongue     -     cannot roll tongue

If they have a child, the possible combinations are:

1)

father's gene: can roll tongue

mother's gene: can roll tongue

RESULT = THE CHILD WILL BE ABLE TO ROLL HIS/HER TONGUE

2)

father's gene: can roll tongue

mother's gene: cannot roll tongue

RESULT = THE CHILD WILL BE ABLE TO ROLL HIS/HER TONGUE

3)

father's gene: cannot roll tongue

mother's gene: can roll tongue

RESULT = THE CHILD WILL BE ABLE TO ROLL HIS/HER TONGUE

4)

father's gene: cannot roll tongue

mother's gene: cannot roll tongue

RESULT = THE CHILD WILL NOT BE ABLE TO ROLL HIS/HER TONGUE