How does the size of a genus affect anticipation in patent law?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

The size of a genus can significantly affect anticipation in patent law. Generally, a smaller, more limited genus is more likely to anticipate a species within it than a large or undefined genus. The MPEP notes:

“[H]ow one of ordinary skill in the art would understand the relative size of a genus or species in a particular technology is of critical importance.” (MPEP 2131.02)

When a genus is very large or encompasses a vast number of compounds, it’s less likely to anticipate a specific species. However, if the genus is small and well-defined, with a limited number of possible variations, it’s more likely that a person skilled in the art could “at once envisage” all the species within it, potentially anticipating a claim to one of those species.