The Federal Circuit continues to tighten the standards for written description of functional claims, particularly in the biologics realm, which is putting patent applicants in the position of having to pursue narrow claims directed to specific sequences. At the same time, reliance on the doctrine of equivalents (DOE) to enforce claims to life science inventions has traditionally been limited. But times may be changing. For example, the 2019 Ajinomoto Federal Circuit case makes it clear that the doctrine of equivalents can apply to sequence-based claims of life science inventions, and a recent Federal Circuit case (Jennewein Biotechnologie GMBH v. ITC, 2020-2220 (Fed. Cir. 2021)) found infringement under the DOE of claims directed to methods involved in producing milk oligosaccharides in bacteria. This suggests a possible uptick in reliance on the DOE the life sciences. Patent strategies should consider including narrower sequence-based claims with the DOE in mind, as we await further developments in the case law.