Gene expression

Consequently, changing how readily transcription occurs can alter the amount of mRNA available and, in turn, the quantity of protein produced. This control of protein production is part of gene expression.

Non-coding DNA does not itself specify that protein’s amino acid sequence, but some of it helps control gene expression. A variant in such a region may stop a gene from being transcribed. The cell then makes no mRNA copy of that gene, so it cannot make the protein from that gene’s instructions.

Even when gene expression changes, the difference may be too small to produce an observable phenotype. The required conclusion is therefore that non-coding variants may influence phenotype by altering gene expression—not that every such variant must do so.