In the real world, our Belief Genome is our sum total of beliefs (content) as well as the structure of these beliefs and the underlying (of higher) laws (or working hypothesis) that function as governance of  these beliefs.

In this virtual world of OSR, The Belief Genome is expressed by hypertext links to Personal Belief Modules - either created by the individual or shared amongst a group of individual.  In other words, the Belief Genome is a COLLECTION of a person's underlying beliefs as expressed by hyperlinks to individual Personal Belief Modules.  Generally, beliefs are shared by a potential network.  The individual can either share and actively participate in this network or remain aloof.  A person who creates a belief might find, over time, that now one else shares this belief.  This person can be seen as a forerunner early adopter of as an isolate.  Not all Beliefs are relevant to everyone and some beliefs will be relevant to no one.  No single belief is relevant to everyone, all the time - forever.

It's not that a Belief Genome physically exists in reality , it's that it is being built or expressed in a virtual environment that has yet to be more fully described (from a non technical POV).