Complex sentence: The genetic code not only controls inheritance: it also controls gene expression, which occurs when a portion of the double helix is uncoiled, exposing a series of the nucleotides, which are within the interior of the DNA.
Split into simpler sentences: The genetic code not only controls inheritance: it also controls gene expression. Gene expression occurs when a portion of the double helix is uncoiled, exposing a series of the nucleotides, which are within the interior of the DNA.