A "sequence variant" is a surrogate term covering any unintentional amino acid substitutions, omissions, or insertions during protein biosynthesis. Production of biotherapeutic proteins by living organisms is governed by biological processes responsible for protein production, including DNA replication, RNA transcription, and protein translation steps. Each of the biosynthesis steps has finite fidelity, with error rates ranging from 10-9 per base pair for DNA replication to 10-4 to 10-5 per codon for protein translation. The occurrence of sequence variants contributes to heterogeneity of recombinant protein therapeutics. Establishing a sequence variant profile of a biotherapeutic product is essential in providing proof of its structure, its manufacturing consistency, and the stability of the producing cell line. DNA mutations can arise during generation of stable producing cell lines and be amplified by selection pressures used to establish high-producing clones.