Why do you only need one copy of a dominant trait gene to have that trait?

Natalie had random hand movements when she was two months old. when she was six months old, she used to grab a block with her whole hand. now at the age of ten months, she can grasp the same block with her thumb and forefinger. this sequence of growth in her hand and finger movements is according to the pattern.

What is the most appropriate method of gaining weight (muscle mass)

Anton created a chart listing different types of materials. which best complete the chart?