Question

If G is the dominant gene for the left thumb, what is the theoretical probability that a child will naturally place the left thumb on top, if the father has gene pair Gg and the mother has gg?

Answer 1

Most likely because the father has the more dominate gene but it coul d be the mother gene 

Answer 2

Cross:  Gg   *   gg

Offspring: Gg, Gg, gg, gg

Favorable Outcomes for Left thumb (with "G" ) = 2

P = 2/4 = 1/2

In short, Your Answer would be: 1/2 or 50%

Hope this helps!