When do members of a Markush group share a ‘single structural similarity’?
Members of a Markush group share a “single structural similarity” when they belong to the same recognized physical or chemical class or to the same art-recognized class (prong 1) and the members of a Markush group share a common function or use when they are disclosed in the specification or known in the art to be functionally equivalent (prong 2).
The answer to this question can be found in chapter 2100 of the MPEP. This chapter covers Patentability.
The answer is from the 9th Edition, Revision 10.2019. Depending on future changes to the MPEP, the question and answer may or may not be applicable in later Editions or revisions.
This question and answer come from section 2117 of the MPEP. The following is a brief summary of section 2117.
2117 Markush Claims
A “Markush” claim recites a list of alternatively useable members. The listing of specified alternatives within a Markush claim is referred to as a Markush group or Markush grouping. This section delves deeper into Markush claims.