1) Genes are transcribed into segments of RNA (ribonucleic acid), which are translated into proteins. Both RNA and proteins are products of the expression of the gene and, in some cases, can be quantified to determine the activity of the gene; abnormal amounts of gene product are often associated with the presence of a disease-causing mutation.

2) The biochemical material, either RNA or protein, resulting from expression of a gene. The amount of gene product is used to measure how active a gene is; abnormal amounts can be correlated with disease-causing alleles.