How is the pan genome differentiated for a given species?

The correct answer is "The pan genome is unique of a species because it is the sum of all the genes that are present in a species, including all the strains within the species clade".

Explanation:

The pan genome is unique of a species because it is the sum of all the genes that are present in a species, including all the strains within the species clade. The pan genome, also known as supragenome, includes not only the core genome, but also the variable or accessory genome that only certain members have. The pan genome is particularly complex for organisms living in multiple environments, for instance microorganisms that habit mixed microbial communities that exchange genetic information among them.