Family resemblance, very evident in this photograph of four sisters, results from having genes in common. Genes must be expressed to exert an effect, and proteins regulate such expression. One such regulatory protein, a zinc-finger protein (zinc ion is blue, protein is red), is shown bound to a control region of DNA (black).
[(Left) © Nicholas Nixon, courtesy Fraenkel Gallery, San Francisco. (Right) Drawn from 1AAY.pdb.]